ANNUAL REPORT 1994
Research Station for Fruit Growing Brugstraat 51 4475 AN Wilhelminadorp The Netherlands
Phone 31-0113-242500 Fax 31-0113-242650 Postgironr 495017
Information contained in this report may not be reproduced in total or in part without permission. Neither the authors nor the Research Station can accept any liability of loss, damage or injury resulting from the application of any concept or procedure in or derived from any part of this report.
ISSN 1381-6594 Price Dfl 25.00 CONTENTS PAGE
Remarks on the brands of pesticides and herbicides 1 Donor Members 1 Board 2 Staff 3 The Experimental Garden Weather and full bloom data 6 Department of Pomology and Economics
Top Fruit and Nursery Rootstocks and interstems for pome and stone fruit 9 (new pear rootstocks - new apple rootstocks - breaking force pear cultivars on Quince MC) Unusual fruit crops 13 (Hazelnut - walnut -Actinidia - quince - Japanese pear) Fruit-tree nursery 16 (national trial with apple-plant material - branching trials with BA)
Planting systems 20 (planting systems with Jonagold, Fiesta and Elstar - planting systems with pear - light measurements with Elstar on commercial fruit holdings)
Evaluation chemical thinners 26
Pruning and tree shapes 27 (root-pruning - fruit firmness after root-pruning - growth control with pear)
Black skin coloration in pear 33 (effect of gibberellins - place of discoloration - relation with cropping level - fruit analysis)
Evaluation of Top Fruit Cultivars Cultivar testing with apple 36 (cultivar trials in Wilhelminadorp - clone trial Wilhelminadorp - clone trials regional experimental gardens)
Cultivar testing with pear 48 (cultivar trials in Wilhelminadorp - clones of Doyenné du Comice - regional cultivar trials)
Cultivar testing with stone fruit 55 (cultivar trials with plum in Wilhelminadorp - cultivar testing cherry in Ahrweiler (Germany) - cultivar testing cherry in Rillaar (Belgium))
The pollination of pome and stone fruit 57 (crossings)
Small Fruit Strawberry cultivar trials 59 (glasshouse strawberries - cultivars in the open)
Cultivar trials of bush and cane fruits 61 (red currant - black currant - gooseberry - raspberry - blackberry)
Development of methods for an early and late harvest of currants, raspberries, blackber ries and blueberries 69 (raspberry - red currant)
Disaese-free propagation of strawberries and other small fruits 71 (influence of light intensity duting the growth of runner plants - unrooted cuttings: growing indoors or in the open - plant density and choice of substrate - illumination of tray plants - influence of gibberellin treatment on flower initiation - lifting dates of tray plants for cold storage - use of tissue-culture plants of Elsanta)
Optimizing closed growing systems in strawberry culture 73 (illumination and cold-units)
Economics and Farm Management Analysis Economic calculations on high density plantings 74 (economic calculations on high density apple plantings - economic calculations on high density pear plantings)
Effect of light in intensive orchards 79 (combination of light model and investment model)
Prediction of optimum picking time of pome fruit 79 (relation price-quality for Elstar and Jonagold)
Effect of agricultural and environmental policy on fruit industry 80
Decision support systems in fruit growing 83 Plant Nutrition and Fruit Quality
Physiology Fruit ripening as affected by environmental factors 84 during growing season (the effect of temperature later in the season on some of the ripening and quality criteria in apple)
Lateral shoot formation in young fruit in the nursery 86 phase (lateral shoot formation in apple in the first year after budding as affected by soil temperature in relation to time of year - the effect of air and soil temperature on compatibility of a few pear cultivars on rootstock Quince MC) Storage and Quality Optimum storage conditions and the suitability of storage techniques for fruit 88 (Doyenné du Comice - red, pink and white currants)
Superficial scald on Jonagold 92
Reduction in fungicide use in spray scheme for controlling storage rot 94 (ULO storage of non-sprayed apples)
Reduction of internal disorders during storage of Conference pear 96 (aim - set up - results)
Skin spots on Elstar 97 (aim - storage conditions research in Geldermalsen and Wilhelminadorp - results - cluster research - curant advice)
Soil Science and Plant Nutrition Control of growth and production of pit and stone fruit by water and nutrient supply 100 (advisory system for the water supply)
Improvement of the advisory system for fertilization, irrigation and soil management 102 (trace elements)
Crop Protection
Spraying Techniques Testing and development of application techniques in crop protection 104 (emission to soil - spray volume - comparison of spraying devices)
Phytopathology and Weed Control Biology and control of secondary or sporadic disease in fruit crops 108 (fireblight on apple and pear - Phytophthora rot in apples - flower bud necrosis on pear - root rot in pear)
Testing of insecticides, fungicides and bactericides in fruit growing 110 (residual activity of fungicides - post-infection activity of fungicides - DMI resistance in Venturia anaequalis - Captan less effective? - fruit colour)
Supervised control of scab 111 (ascospore flights - scab infections - accelerating leaf drop - effect of planting system)
Biological control of diseases in fruit crops 113 (canker on apple -scab on apple)
Entomology and Biological Control Integrated control of pests on top fruits 114 (apple casebearer - mullein bug) Biology and control of rosy apple aphid Dysaphis plantaginea 115
Biological control of pests on strawberry and soft fruits 116 (garnation leafroller)
Integrated fruit growing 117
(farming systems research) List of Chemicals 127 List of Entries 129 Publications 139 Bulletins and Publications on Fruit Growing 145 Remarks on the brands of pesticides and herbicides
The dosages mentioned for pesticides and herbicides in this report refer to the commer cial products. Trade names of products have been used for the sake of convenience, but this makes it unavoidable that in some cases similar endorsement of named products is intended. Some of the experiments described in this report are carried out with chemicals and/or concentrations not yet legally improved.
Donor members
Those who are interested in the work of Research Staion and wish to keep an active touch with and support its research, are invited to become donor member. Donor members will receive the Annual Report and other publications of the Research Station without charge. The minimum subscription for donor membership is 35 guilders for private individulas in The Netherlands, 60 guilders for institutions in The Nether lands, and 50 guilders for foreign private individuals and foreign institutions, annually. Paymant by transfer to an account of the Proefstation voor de Fruitteelt (post office giro account nr. 49 50 17, account ABN/AMRO-bank Goes nr. 47.21.74.878) or by international postal money order in Dutch currency, payable to the Proefstation voor de Fruitteelt at Wilhelminadorp, with the indication "Donorship Subscription". Board (31 december 1994)
Board of the foundation research station for fruit growing
Executive committee Other members
J.A.M. Musters, Dinteloord, chairman FJ. van Beerendonk
H.W.M. Kurver, De Meern, vice-chairman G.A. van Haarlem
A.H. Tap Dodewaard, secretary A.G.W, van Kempen
Ir. H.R. Kuypers
Advisors Ing. C.G.M, van Leeuwen
Ir. J.M. Gerritsen Ir. H.T.J. Peelen
Dr. ir. G. Weststeijn H.F.M. Schrama
J. Zevenbergen G. de Weert
Ir. R.J.M. Meijer Ir. C.M.M, van Winden
J. van Woudenberg
vacancy Staff (31 december 1994)
Research Station for Fruit Growing Director: R.J.M. Meijer Research co-ordinator: Ir. J.A. Jobsen Pomology and Economics Dr.lr. S.J. Wertheim (head, deputy director)
Top Fruit and Nursery Dr. Ir. S.J. Wertheim Mw. Ing. J.M.T. Balkhoven-Baart Mw. Drs. P.S. Wagenmakers J.M. de Groene M. Tazelaar Evaluation Top Fruit Cultivars Ing. P.D. Goddrie Ing. H. Kemp Small Fruit Ir. J. Dijkstra A.A. van Oosten Economics and Farm Management Analysis J. Goedegebure Mw. Ir. M.J. Groot Library and Editorial Staff Mw. M.M. Cremers-van Scherpenzeel Plant Nutrition and Fruit Quality Dr.lr. A. de Jager (head)
Soil Science and Plant Nutrition Ir. M.P. van der Maas Ing. P.J. Bolding Physiology Prof. Dr. J. Tromp Ch.A.R. Römer Storage and Quality Dr.lr. A. de Jager Ing. F.P.M.M. Roelofs Ing. H. de Putter L. de Pagter Laboratory Mw. Ing. L.M. van Westing (head) Mw. M.T.T. de Leeuw-Vereecken Mw. A.M. Meerman-van de Repe Mw. P.C. Rijk Mw. D.T. Slazak Mathematics and Statistics E.M.A. van Remortel
Crop Protection Ir. B. Heijne (head)
Spraying Techniques Ir. B. Heijne Phytopathology and Weed Control Drs. H.A.Th, van der Scheer H.J. Wondergem Ir. H.J. van Hartingsveldt Mw. J.J. Slabbekoorn Entomology and Biological Control Ir. J. Woets W. Remijnse Integrated Fruit Control Mw. Ir. A.M.E. Schenk Data Management W. Beeke Administration and Support Services J.A.M. Kouwenberg (head)
Administration Mw. A.M.Th. Mateijsen Mw. T.L. Buizer-Schuit Mw. M.C. Schrier-Nijssen Mw. J.G. Snaterse-van Loo Mw. P.E. van Vossen-Hopmans Mw. M.S. Westerweele-Korsuize Housekeepers Mw. D.N. Nijsse-Hoogesteger Mw. M.M. Stuck
Experimental Garden and Engineering J.L. Baarends (head) J. de Schipper D.R.M. Acda R.H.N. Anbergen A.A. Janse M.C. van Maris P.C. Oostdijk S. Smits J. van Dalen Regional Experimental Orchards
Stichting Proeftuin Noord-Brabant, Breda Ir. G.J. Staring (director) H.M.C. Nuyten Ing. Sj. Rinsma A.C. Oomen
Stichting Fruitteeeltproeftuin Midden-Nederland, Geldermalsen Ir. J. Geervliet (director) G.J. Alink A. Scholtens CK. van Zuidam W.C. van Eldik C.C.M. Sturkenboom
Stichting fruitteeltproeftuin voor Limburg en Noord-Brabant, Horst Ir. J. Geervliet (director) Th. Veens Mw. Ing. W.A.G.M. Jansen F. Jacobs H. Mertens
Fruitteeltproefbedrijf van de Vereniging "Naar Beter Fruit", Numansdorp Ir. G.J. Staring (director) J. Westerlaken Mw. Ing. E.A. van Hermon H. Veijer A. de Bes P.L. Leeuwenburgh
Stichting Fruitteeltproeftuin voor Noord-Nederland, Zeewolde Ir. A.P.M, van Dongen (director) W. Lugtenberg Ing. J.H. Bootsma Mw. J.J.H. Dekker-Kets E. Klagelhout V. Schoutsen Division Fruit Production of the National Reference Centre for Arable Farming and Horticulture Ir. R.K. Elema (national fruit advisor) Ir. P.A.M. Besseling (fruit industry economist) A.J.P. van der Waart (fruit growing and quality expert) Ir. E.J.M. Regouin MSc. (crop protection expert) Ing. J. Kodde (soil, water and plant nutrition expert) M.L. Joosse (farm economics expert) Mw. M.T. Kruijssen (administrative officer) The experimental garden
Weather and full bloom data P.S. Wagenmakers Table 1 lists data on global radiation, precipitation, temperature and full bloom for Wilhelminadorp. Long-year averages were presented for Vlissingen because these data were missing for Wilhelminadorp. Because Vlissingen is closer to the North Sea, slight differences occur between the two stations. The significance of these on fruit perfor mance is, however, small.
Table 1. Mean daily temperature (1994 and long-year average) Wilhelminadorp (Wi) and Vlissingen (VI)
Month Global radiation Precipitation Temperature (MJ/m2/month) (mm) (°C)
Wi VI Wi VI Wi VI 1994 1951- 1994 1951- 1994 1951- 1990 1990 1990
January 68.8 78.8 78.8 65.9 5.7 3.1 February 134.7 143.6 40.5 46.3 2.5 3.1 March 261.3 274.4 72.1 55.9 7.7 5.2 April 413.1 412.0 76.3 45.6 8.6 8.0 May 536.7 563.9 64.5 46.5 12.5 11.9 June 588.0 587.1 51.3 63.6 15.4 14.9 July 698.3 563.4 15.5 68.7 20.7 16.7 August 487.0 489.1 61.3 80.1 18.1 17.0 September 265.9 342.7 169.8 70.9 13.9 15.2 October 203.1 209.6 88.6 81.4 10.2 11.7 November 87.8 97.5 33.9 76.9 10.3 7.2 December 60.7 61.7 121.2 72.9 6.2 4.5
As in previous years, The winter of 1993-1994 was warm. Temperatures between November and March were 2-3 degrees warmer than "normal". Only February was cool. There was heavy rainfall in spring and mean temperatures were slightly higher than normal. At bloom (end of April, beginning of May) temperatures were several degrees higher than normal, but the second half of May and also in June these were normal. July was very sunny, warm and dry. These conditions were also observed in August, but the weather changed in September. There was a lot of rainfall in this harvest month, and the weather was cold. October was also cold, but as wet as September. November and December were quite warm again. temperature °C
OW
25 • • m •
• #• X 20 '1S>" X • ' daytemp.'M TF' '\ - 15- .A \mMt, • ~"WMkav«.*9 4 • ".* • / •^- • *v •• * — av«.1951-'90 % I 10- • 'SX 'J ' VA •7 • ^' - - ; 5
1-4 1-5 31-5 30-6 30-7 29-8 28-9 28- 10
date (1994)
Figure1 . Mean daily temperature (1994 andlon g year average)
The mean annual temperature was 1.1. degree above the long-year average. Therewa s 874 mm precipitation, 100 mm more than normal. Incoming radiation was normal for the growing season (between Mayan d September) aswel l asfo r theentir e year. Bloom
Bloom was quite early in 1994 (Table 2).
Table 2. Data of full bloom at Wilhelminadorp (plum, pear, apple)
Cultivar 1990 1991 1992 1993 1994 1973
1992
Opal 21-4 8-4 11-4 9-4 15-4 19-4 Victoria 21-4 8-4 12-4 4-4 13-4 18-4
Conference 2-4 12-4 20-4 16-4 20-4 25-4 Doy.d.Cornic e 2-4 14-4 26-4 20-4 27-4 30-4
Alkmene 12-4 17-4 1-5 25-4 4-5 5-5 Elstar 16-4 29-4 4-5 28-4 9-5 11-5 Jonagold 19-4 29-4 2-5 25-4 4-5 10-5 Golden D. 22-4 25-4 3-5 27-4 9-5 10-5 Pomology and Economics
Top fruit and Nursery
Rootstocks and interstems for pome and stone fruit
S.J. Wertheim and J.M.T. Balkhoven-Baart
New pear rootstocks
Trial 044 9111 The trial with three new French pear rootstocks (OH11, OH20, OH33) planted in the spring of 1991,bot h in Wilhelminadorp and in Angers in France, had not yet rendered a good dwarfing rootstock (Table 3). With Conference the standard Quince MC was still the most dwarfing and precocious rootstock which also gave, together with BA 29 the only other quince rootstock in the trial, the largest pears. With Pierre Corneille, however, OH20 proved more dwarfing and productive than Quince MC, which is quite remarkable for a pear rootstock, but the pears were smaller than those obtained from trees on the other rootstocks.
Table 3. Results pear-rootstock trial 044 9111
Rootstock Tree Kg/ Fruits/ Weight volume/m3 tree m3 fruit (g) 1995 1992 to 1994
Conference Quince MC 1.28 a 19.4 75.9 a 186 OHxF333 1.64 b 15.2 45.7 b 165 0H20 1.67 c 12.0 41.3 b 164 BA29 1.77 be 15.4 44.3 b 188 OH11 1.96 cd 18.3 45.6 b 175 OH33 2.17d 6.2 15.1 c 175 LSD005 0.30 19.5 Pierre Corneille Quince MC 1.98 be 34.3 69.8 ab 242 OHxF333 1.78 ab 21.8 51.1 cd 231 OH20 1.55 a 22.9 80.4 a 194 BA29 1.92 b 31.6 57.5 bc 231 OH11 1.97 be 27.9 70.7 ab 236 OH33 2.27 c 21.5 39.6 d 232 LSD0.0B 0.34 16.9 Values in one sub-column followed by the same letter(s) do not differ significantly (P 0.05) Trial 044 9112
The trial with the French pear rootstock RV139 was ended prematurely, because this rootstock proved too dwarfing. Table 4 shows how thin the trunks were after four growing seasons and how low the production was compared with Quince MC. Photo 1, also shows the poor tree volume on RV139 that was obtained even with the most vigorous cultivar Beurré Hardy. Moreover, the propagation of RV139 proved extremely difficult, even 'in vitro'.Two cultivars were budded on the English quince rootstock QR193-16, which grew equally as vigorously as with Quince MC, but was less precocious. This rootstock remains under investigation in other trials.
Photo 1. The vigorous cultivar Beurré Hardy on rootstock quince MC (left), and the dwarfing French rootstock RV 139 (right)
10 Table 4. Results pear-rootstock trial 044-WI9112
Rootstock Trunk Increase Kg/tree circ. trunk circ. 1992 till 1994 (cm) (cm) 1995 1991-1995
Beurré Hardy Quince MC 21.6a 16.6 a 12.8 RV139 8.8 b 4.9 b 2.8 LSD005 1.18 1.41 Conference Quince MC 16.0 a 10.5 a 29.6 RV139 6.6 b 2.9 b 2.8 QR193-16 15.3 a 10.0 a 22.9 LSDo.05 1.38 1.41 Doyenné du Cornice Quince MC 19.7 a 13.1 a 15.3 RV139 6.0 b 2.7 b 2.2 QR193/16 20.1 a 14.2 a 9.0 LSD005 1.32 1.41 Gieser Wildeman Quince MC 16.4 a 11.1 a 15.8 RV139 6.7 b 3.3 b 1.9 LSDo.05 1.25 1.60
Values per sub-column followed by the same letter(s) do not differ significantly (P 0.05)
Newtrials
In the spring of 1995 a small trial was planted with Conference as test cultivars wherein the Polish quinces S1 and S3 will be compared with Quince MC. The plant material consisted of two-year-old trees. In a second trial, commonly carried out with HRI at East Mailing, U.K., Doyenné du Comice is the test cultivar and QR193-16 and Quince MC, both budded at 15, 30, and 45 cm, are the treatments. Here, the trees were one-year-old and extremely well feathered. The aim of both trials is to find alternative ways for chemical growth control as Quince MC is still too vigorous a rootstock.
New apple rootstocks
In the spring of 1995 a trial was planted with some new apple rootstocks, namely CG65 from a breeding programme at Cornell-Geneva (USA) and the Pi-Au numbers 7- 33, 9-16, 9-82, 51-11, and 56-83 from a breeding programme at Dresden-Pillnitz (Germany). In Wilhelminadorp one-year-old trees of Golden Delicious 'Reinders' were planted and in Zeewolde one-year-old trees of Elstar with M.9 as astandard .
11 Table 5. Results break test pear cultivars on Quince MC
Cultivar Graft number Force Comp- 1 2 3 4 5 kg*) ati- bility#
Beurré Hardy 15 9 3 3 0 76,5 g Saint Rémy 15 1 5 9 0 63,9 m Le Curé 12 1 3 8 0 60,9 g Condo 14 0 10 4 0 60,6 ? IVT 69013-18 15 1 7 7 1 51,3 ? Winterrietpeer 14 1 5 8 0 58,5 p Concorde 16 0 4 12 1 50,1 ? Doyenné du Cornice 9 0 4 5 1 47,7 g Zoete Brederode 12 0 5 7 1 47,6 m Conference 14 0 5 9 2 45,2 m Clara Frijs 16 0 0 16 0 45,0 g Packham's Triumph 14 0 0 14 1 44,4 g Abate Fetel 19 1 4 14 4 44,2 p Bon Chrétien Williams 10 0 6 4 1 43,9 p Charneux 18 0 4 14 2 41,8 p Bonne Louise d'Avr. 15 0 3 12 1 41,5 m Beurré d'Anjou 16 0 5 11 1 41,3 m IVT 6403-23 13 0 8 5 1 40,9 ? Pierre Corneille 12 0 0 12 3 39,8 g Clapp's Favourite 16 0 4 12 2 39,3 p Dolacomi 14 0 3 11 3 38,8 ? Beurré A. Lucas 12 0 6 6 2 37,7 m IVT 69007-36 15 0 5 10 1 37,4 ? Beurré Bosc 15 0 1 14 5 37,0 P Republica 13 0 3 10 4 36,8 P Beurré Clairgeau 13 0 2 11 2 35,6 P IVT 66006-273 16 0 13 3 2 31,3 ? Triomphe de Vienne 14 0 5 9 4 31,1 P Sierra 20 0 0 20 9 31,0 P Précoce de Trévoux 14 0 2 12 6 30,7 m Cascade 16 0 4 12 8 28,6 P Gieser Wildeman 12 0 0 12 9 25,3 P Baurotard 15 0 2 13 9 25,1 P columns = total number of grafts; = number of grafts that did not break at 80 kg (maximum Instron); = number of grafts that folded and were discarded; = number of grafts that did break well from the rootstock; = number of grafts that broke with little force (< 30 kg), means of columns 2 (= 80 kg), 4, and 5. #) literature data on compatibility: g = good, m = moderate, p = poor, ? = unknown.
12 Breaking force pear cultivars on Quince MC
In August 1992 a range of pear cultivars (Table 5) was budded onto Quince MC rootstock. In the autumn of 1994, all trees were grubbed and underwent a break test with the Instron, an apparatus to determine break forces. Scion and rootstock were cut back about 10 cm from the union and the rootstock was set in a small bench-vice in such a way that the rootstock and scion were in a horizontal position with the place of budding directed downwards. The vertical plunger (diameter 12.7 mm) of the Instron apparatus was moved downwards at a constant speed so that it landed circa 1 cm above the union. The force at the moment of the breaking of the scion from the rootstock was recorded automatically. On a few occasions the scion did not break from the rootstock at the maximum force of 80 kg. For these grafts 80 kg was taken for the calculation of the average force. This occurred especially with Beurré Hardy (Table 3), a sign that this cultivar grew together very well with quince. More often it occurred that scions did not break from the rootstock but folded double (Table 5). These were discarded from the calculations. Cultivars that showed this rather often are not very suitable for a break test (Condo, Bon Chrétien Williams, IVT 6403-23, IVT 66006-273). Not mentioned in Table 5 is IVT 68013-38 because all 15 scions folded double, so no breaking force could be determined. Table 5 also mentions the number of scions that broke from the rootstock with a small force (< 30 kg), a sign of poor fusion. In broad outline the results of the test were in agreement with the data from the literature on compatibility. For example, Beurré Hardy and Le Curé, known interstem cultivars, had a high breaking force. Also, most incompatible cultivars had low breaking forces and high number of grafts that broke out easily. Winterrietpeer was an excepti on. The reverse was true for the compatible Pierre Corneille that ended up rather low in Table 5. The method was meant to determine quickly whether new cultivars fuse well with quince in other words, do or do not need an interstem. Some of the new cultivars like Concorde and some IVT-numbers apparently do not need an interstem, but for other IVT-numbers a interstem seems appropriate. The method seems useful when both the breaking force and the number of grafts that break easily are considered. The test method should be improved in order to prevent folding of the scions and to decrease variation in breaking force within one cultivar.
Unusual fruit crops
S.J. Wertheim, J. Dijkstra and H. Kemp
Hazelnut (Coryllus sp.)
S.J. Wertheim
Thehaze/nut trial of 1982
From this trial planted in 1982, only five cultivars remained in 1994 (see Annual Report 1993, p.18) . In 1994, all cultivars produced much less than the year before, a biennia- lism quite common in hazelnut. The percentage of empty nuts was also quite high in 1994 (Table 6). At the end of 1994 Butler was grubbed. Although Butler proved quite
13 productive, kernel quality was not good enough since the pellicles could not be removed during roasting. Tombul, too, was not a good cultivar in Wilhelminadorp, because productivity was far too low. Negret was reasonably productive, although 1994 was an off year, an expected phenomenon after the abundant cropping in 1993. Negret had good kernel quality. Lang Tidlig Zeller was productive and, moreover, every year drops almost all nuts without the husk. A disadvantage was that the kernels did not blanch well during the roasting process. Gustav's Zeller was the best cultivar from this trial; it was productive and the kernels were of high quality.
Table 6. Results 1994 hazelnut trial 052 8281
Feature Butler Gustav's Lang Negret Tombul Zeiler Tidlig Zeiler
% free husking 78 48 97 70 4 % empty shells 28 22 33 18 54 Nut weight* g 4.92 4.42 4.03 2.41 1.67 Kernel weight g 4.18 2.80 3.13 1.62 1.53 % kernel" 63 53 60 59 64 Nuts/tree" 244 881 530 134 162 Kg/tree* 1.65 4.65 2.73 0.36 0.34 Blanching index* 3.7 9.0 4.7 9.0 9.0
full nuts, "'kernel weight/full-nut weight)x100. * after roasting, scale 1 = no blan ching to 9 = complete blanching.
Hazelnuttrial 1983
The production in 1994 was low with 0.15 kg full nuts per tree for Tonda Romana, 0.55 kg for Morell, 0.60 kg for Mortarella, and 0.81 kg for Romai. Given the producti ons obtained so far none of the cultivars are good enough under Dutch conditions.
Hazelnut trial 1988
Here too, a number of cultivars produced less than in 1993. Camponica gave the highest yield (1.09 kg full nuts per tree). The production figures were reasonably good for Nocchione (0.91 kg), Tonda di Giffoni (0.80 kg), and especially good for Gustav's Zeiler (0.73 kg), because the latter was only planted in 1991. Pauetet lagged behind with 0.33 kg per tree. With the exception of Nocchione the kernels of all cultivars blanched well during roasting. The trial is still too young for final conclusions.
Hazelnut trials 1989 and 1990
Most cultivars gave some crop in 1994. From the cultivars planted in 1989 the Italian Riccia di Talanico and the Dutch Emoa 1 were most productive with 166 and 165 full nuts per tree respectively. From the cultivars planted in 1990 the American OSU 23-17 had the highest productivity (256 good nuts per tree). The Dutch Emoa 3 planted in 1991 also yielded well with 169 full nuts per tree. The trials are too young for final
14 conclusions. In the spring of 1995 a comparison trial was planted with 14 selections from the breeding programme of Dr. S.A. Mehlenbacher from Oregon State University.
Walnut (Juglans regia)
S.J. Wertheim
The experiences with the walnut-cultivar evaluation up to 1994 were summarized for a poster for the international ISHS walnut symposium to be held in Portugal in June 1995. The readers are referred to this text that will be published in the appropriate volume of Acta Horticulturae, that will appear after this meeting. From all cultivars tested so far, Broadview was the most productive. Whether a commercial walnut culture is feasible under Dutch conditions will depend on the price of the walnuts. With a production level of 3 tonnes of sound nuts per ha, a level reached during the last years, six guilders per kg is needed for an economic perspective. If yields were a little higher (4 tonnes) due to denser planting (200 trees per ha), which seems feasible in the case of the non-vigorous Broadview, a price of five guilders per kg will be sufficient.
Actinidiaspecie s
J. Dijkstra
Siberian gooseberry(Actinidia arguta)
Yield of the 12-year-old bushes of cv. Ananasnaya on plot 22 was somewhat disap pointing: the average production was 5 kg per bush. Also, the average fruit weight was low (1994: 7.5 g, 1993 10.7 g). Probably, pollination was not optimal, as Ananasnaya did not flower at the same time as the male pollinators. Harvest date was normal (29th September). The impression is that no pruning or very slight pruning has a positive influence on yield. However, no pruning gives a very dense growth with a lot of dead wood inside the bushes.
Mandsjourian gooseberry(Actinidia kolomikta)
Due to spring frost at a very early stage no fruits could be harvested. Also, growth was only moderate.
Quince (Cydonia ob/onga)
H. Kemp
The fourteen cultivars from the trial planted in 1988 (052-WÎ8882) cropped well in 1994, but Agvambari and Rea's Mammoth were again the highest croppers (with 28.9 kg and 33.8 kg per tree respectively). The fruit of Agvambari is relatively small but attractive. Fruit of Emek stored well at 1 °C. In 1994, Ludovic, Rea's Mammoth, Ronda, Shams and Vranja were analysed for vitamin C, dry matter, and mineral content. Ludovic and Lescovacka were lower in vitamin C, Agvambari, Bourgeault and Rea's
15 Mammoth were higher. Bourgeault had a conspiciously high content of Ca. The same was true for N with Ludovic. Vranja had a low content of P and K. Dry-matter content hardly differed.
Japanese pear {Pyrus pyrifolia)
H. Kemp
The cultivar trial planted in the spring of 1990 (052-WÎ9013) with table grafts on Pyrus betulifolia (Hayatama on Pyrus communis) had to be prematurely terminated due to cuts in the budget of the Research Station. All trees were trained in a V-hedge planted at 3.5 m x 3.00 m to prevent damage by rubbing on the fruit. In 1992 only Niitaka and Kosui gave fruit; in 1993 all cultivars except Hosui and Hayatama did so. In 1994 again Hayatama did nit crop as well compared with all other cultivars. Table 7 summarizes some main results.
Table 7. Results evaluation Japanese pear cultivars
Cultivar Trunk circ. Kg/tree Mean fruit (cm) 1992-1994 weight (g) autumn 1994 1993-1994
Kosui 15.9 12.4 126 Hosui 17.2 0.1 200 Shinko 15.0 1.8 274 Shinsui 16.2 2.5 138 Shinseiki 15.3 11.3 182 Chojuro 17.5 2.7 244 Tama 12.6 9.2 119 Niitaka 14.4 10.2 230 Hayatama 10.8 0.0 —
Hayatama (on Pyrus communis) grew clearly less well than all other cultivars. Kosui and especially Tama showed symptoms of iron deficiency, both in 1993 and 1994. Possibly therefore, growth of Tama lagged behind. Chojuro and Kosui tasted fairly well in 1993 and 1994, and better than Niitaka. Given the demands of the average Dutch consumer it is highly doubtful whether a culture of Nashi pear can become a profitable activity. Possibly, for decorative purposes a small-scale culture can be considered.
Fruit-tree nursery research
S.J. Wertheim and J.M. de Groene
National trial with apple-plant material
In the spring of 1988 a national trial was planted in four regional experimental gardens (Geldermalsen, Horst, Numansdorp, and Zeewolde) with four apple cultivars (Elstar, Golden Delicious 'Smoothee', Cox's Orange Pippin, Jonagold) all on rootstock M.9,
16 comparing three different types of plant material each in three tree-quality classes based on the number of feathers per tree (Table 8). The plant material was raised in the same nursery and was ready for planting in the orchard in the spring of 1988.
Table 8. Treatments apple plant-material trial 054-WI8802
Number of feathers/tree (> 10 cm) Num- Type Elstar Golden Cox's O.P. Jonagold ber ") Ho Nu Ho Nu Ge Ze Ge Ze
One-year-old trees 1. I 7.7 4.8 4.7 5.1 5.8 6.2 5.3 6.3 2. m 10.3 8.1 7.7 7.3 8.3 8.9 7.9 8.9 3. g 13.2 11.3 9.7 9.3 13.0 11.2 9.1 10.5 Interstem trees 4. I 8.9 6.1 8.5 6.9 8.3 6.3 6.2 7.8 5. m 11.2 9.7 10.9 9.7 10.4 8.5 8.9 9.7 6. g 16.3 11.9 13.0 11.3 14.2 10.2 11.2 10.6 Snip trees 7. I 6.6 6.0 6.8 6.3 7.0 7.2 7.3 8.2 8. m 10.1 9.3 9.3 9.7 10.7 9.3 9.9 10.2 9. g 13.8 12.8 11.7 10.7 14.1 11.0 12.3 10.6
*) degree of feathering: I =light , m =moderate , g = good
In the case of the one-year-old trees rootstocks were planted in the spring of 1986 and the cultivars were budded at 1 5 cm above ground level in August 1986. The rootstocks were headed back above the buds in the spring of 1987. In 1987 the scion developed into atre e that was grubbed in the winter 1987/'88. In the case of the snip trees, the rootstocks were planted one year earlier in the spring of 1985. Budding was done in August 1985 at 15 cm above the soil. The buds grew to a one-year-old tree in 1986. In the spring of 1987 the trees were headed back to a height of 50 cm above the soil and only the highest bud was allowed to develop. This bud gave a one-year-old head at the end of 1987 at which time the tree was grubbed. The interstem trees also required planting of the rootstocks in the spring of 1985. In August 1985, the interstem cultivar Dubbele Zoete Aagt was budded at 15 cm above the soil. In August 1986, the interstem was budded at 50 cm above the soil with the scion varieties. In the spring of 1987 the interstem was headed back to the bud of the scion variety. These scions grew to one-year-old heads in 1987 and the trees were grubbed also in the winter of 1987/'88. In three gardens the treatments occurred in six reps of three trees per plot, but in Geldermalsen four reps of three to four trees per plot were present. Planting distances were: 3.50 x 1.50 m (Ho), 3.00 x 1.20 m (Nu), 3.25 x 1.25 m (Ge), and 3.00 x 1.30 m (Ze). The trial was ended at the end of 1992. Due to interactions it was not possible to analyse the production data for all sites and cultivars. Table 9 gives the statistical analysis to that was possible.
17 Table 9. Kg/tree 1989 to 1992 plant material trial 054-WI8802
Type Ho Nu Ze Ge E+ G E+ G Cox Jon Cox Jon
1-yr-ol d 47.9 54.3 56.5 98.6 30.1 57.3 snip tree 49.6 58.7 60.3 104.4 39.8 62.3 interstem 49.8 61.1 68.9 104.7 44.6 71.8 LSDo.05 2.5 2.5 4.4 4.4 4.4 4.4
Feather Ho + Nu Ze+ Ge number E+ G Cox Jon
light 50.5 49.1 81.6 moderate 54.3 51.5 89.8 good 55.8 56.5 89.8 LSD0.0B 1.8 2.8 2.8 Analysis of variance Site * * * # #* Cultivar NS # * * Type * * * * * * Feather number * * * # * * Site*type * * Site* cultivar NS * * Site*feather number NS NS Cultivar *type NS NS Cultivar*feather number NS * * Type*feather number NS NS Site*cultivar* type NS * *
NS = non-significant. *, **, *** = significant at P < 0.05, P < 0.01 or P < 0.001. Other three and four-factor interactions NS.
Although the results were unequivocal, one-year-old trees were the least productive. In Horst the difference with the two other tree types was not significant, and in Zeewolde this was the case with snip trees of Cox. Snip and interstem trees were equally productive in Horst and Numansdorp and in the case of Jonagold in Zeewolde, but in other cases interstem trees were more productive (Cox in Zeewolde and both cultivars in Geldermalsen). The degree of feathering, too, had no defiaite effect, but the tenden cy was for the lightly feathered trees to lag behind in production; in Zeewolde and Geldermalsen the difference with moderately feathered trees was not significant. In broad outline it appears that well feathered snip and especially interstem trees must have preference.
Branching trials with BA
With financial aid from the chemical company Luxan B.V. at Eist the feathering agent benzyladenine (BA) was evaluated on growing buds of six apple cultivars on rootstock M.9 in the fruit-tree nursery. BA was applied two, four or six times in concentrations of
18 150, 300, or 600 ppm active ingredient. Spraying started at 50 or 65 cm plant height. In all sprays 0.1 % Tween 20 was added as a wetting agent. The interval between sprays was one week and at all times only the upper 20 cm of the buds were wetted. Buds that remained untreated or were sprayed once with Promalin served as controls. Spraying from 65 cm plant height was more effective than from 50 cm and therefore only the results from the 65-cm series are given in Table 10. Promalin was not effecti ve, possibly because it was sprayed only once, similarly two BA sprays were less effective than four or six sprays. Table 10 clearly shows the possible increase in number of feathers per tree by repeated BA sprays. Except for Golden Delicious this also held for feathers that developed well above ground level (>80 cm), which are of great importance for future frame branches. For example, after 6 sprays with 600 ppm BA the number of such highly placed feathers was: 7.5 per tree (Cox), 3.5 (Delcorf), 8.7 (Elstar), 0.7 (Golden), 11.1 (Jonagold), and 12.5 (Boskoop).
Table 10. Feathers/tree (>10cm) higher than 50 cm above the soil in trial 054- WI94040 )
Treatment Cox's O.P. Delcorf Elstar Golden Jonagold Boskoop
Control 8.6 1.1 7.4 2.6 8.2 2.3 Promalin* 8.3 2.8 6.1 3.8 9.0 6.4
2x BA150 9.0 3.8 6.6 4.0 8.5 4.6 BA300 8.9 4.4 8.2 7.9 9.0 8.6 BA600 10.3 5.8 9.0 9.1 9.1 9.2
4x BA150 11.9 4.7 10.1 4.8 11.4 6.5 BA300 14.0 6.3 13.3 8.1 13.3 10.9 BA600 12.8 10.1 15.6 10.4 12.7 14.0 6x BA150 15.4 5.1 13.4 5.3 13.9 9.4 BA300 16.6 9.7 15.7 9.6 17.2 16.1 BA600 15.4 10.6 19.6 11.8 18.6 17.5
(LSD005 = 217); " 50 ml/l water with Rode Boskoop and 25 ml/l water with the other cultivars; every time with 0.1 % Tween as wetting agent
BA gave more feathers the more often it was sprayed and the higher its concentration. This also held for the feathers developing higher than 80 cm above the soil. The branch angle decreased with increasing spray numbers and concentration. The average length decreased as well when the number of sprays increased, but increasing the concen tration gave longer shoots. Bud length and trunk diameter were only marginally affected by the treatments. The smaller branch angle caused by the treatments occurred particularly with Elstar. Since this cultivar is already characterized by rather small angles it should be sprayed less often and with lower concentrations than cultivars such as Boskoop and Jonagold which possess wide angles. The optimal treatment varied per cultivar. For Elstar it was 4 x 300 ppm, for Cox between 4 x 300 and 600 ppm, for Delcorf, Golden, and
19 Jonagold 6 x 300 ppm, and for Boskoop 6 x 600 ppm. The chemical company Luxan has asked for an official approval for this branching agent, so currently it is not permitted to use BA in practice.
Planting systems and light utilisation
P.S. Wagenmakers and M.Tazelaar
Planting systems with Jonagold, Fiesta and Elstar
In 1991 a trial was planted with three cultivars on M.9 rootstock at four planting densities (Table 11) and two locations (Zeewolde and Wilhelminadorp). At each density, there were two arrangements, the ratio of distance between and within the row being 1.5:1 (2:1) at 20,000 trees per ha) or 3:1). In addition, in the 3:1 systems vertical and oblique trees ("Güttinger V" with trees alternatingly inclined to left or right) were compared. The angle was smaller at higher densities. Trees were planted as normal (into) or on the soil at Zeewolde.
Table 11. Production and maximum light interception in 1994.
Object Tonnes/ha Light interception Jo-W Jo-Z Fi-W El-Z Jo/Fi-W
Trees/ha 3.000 62.5 61.0 35.7 59.4 58.8 6.000 82.0 90.7 54.2 81.2 71.5 10.000 100.8 86.6 78.5 90.3 83.3 20.000 107.2 75.9 80.6 58.3 87.8 F-test ** * ** * ** * ** * ** * LSD 16.5 13.3 6.9 12.5 5.7
Arrangement 1,5:1 97.9 91.6 62.8 73.6 77.6 3:1 83.1 77.3 63.8 67.3 72.9 3:1, V 83.4 82.8 60.2 74.5 75.6 1,5:1,on soil 68.6 76.6 3:1, on soil 72.4 69.3 F-test — * NS NS NS LSD 14.3 14.8 - - -
Jo = Jonagold, Fi = Fiesta, El = Elstar, W = Wilhelminadorp, Z = Zeewolde. NS = non significant, ~, *, *** differences within a subcolumn not significant or significant at P < 0.10, 0.05 of 0.001 respectively.
Increasing tree number per ha influenced the production positively up to a certain density. At Wilhelminadorp, differences in production between 10,000 and 20,000 trees per ha were small, whereas production did not increase further at densities higher than 6000 at Zeewolde. Here, the production of Elstar even decreased at 20,000 trees
20 interception global radiation (%)
IVV
80-
60-
40-
20-
U 1 1 1 1 1 1 1 1 1 1 i i i 26-4 8-6 10-7 24-8 25-9 31-10 date (1994)
Figure 2. Light interception in 1994. per ha. Zeewolde had more vigorous growth, which explains that the optimum tree density is lower than at Wilhelminadorp. The 1,5:1 systems produced more than 3:1 systems. There was no effect of the V. In 1994, the trees planted on the soil did not produce more than normally planted trees. In previous years, Elstar trees planted on the soil produced 14 % more. There was no significant effect for Jonagold (Table 11). Light interception (465-645 nm), measured at Wilhelminadorp, increased with density from 60 % at 3000 trees per ha to almost 90 % at 20,000, the differences between arrangements being not significant. Light interception, averaged for all treatments, was 52 % in the first week of May, and increased to 69 % by the end of May. Between the middle of July and August, values remained constant (75 %). After harvest, light interception decreased as a result of picking and leaf drop. Fig. 2 illustrates seasonal interception of global radiation (300-3000 nm). Fruits were graded at Wilhelminadorp. There were marked differences in fruit quality between the various densities. In addition the effect of density was not the same for both varieties. Considering background colour, the production of quality fruit (green or yellow-green background colour) was the same for all densities for Jonagold. The production of fruit with a yellow background colour, however, increased with density.
21 At the highest density, almost 50 % of the total production were yellow fruit. This increase of the yellow colour with density was an indirect effect of less red colour. Fruits of the higher densities were picked later to promote red colour formation, but they ripened also. In contrast, the production of Fiesta fruit with a green or yellow- green background colour increased with density. Also the proportion of fruit with a good background colour was considerably higher for Fiesta than for Jonagold. Arrangement had no effect on background colour for both varieties (Table 12).
Table 12. Tonnes/ha of fruit with green or yellow background colour in Wilhelminadorp (1994).
Object Jonagold Fiesta green yellow green yellow
Trees/ha 3.000 26.2 13.8 23.5 4.1 6.000 26.9 30.0 37.6 4.1 10.000 26.5 48.8 58.9 4.0 20.000 28.8 54.9 68.2 2.2 F-test NS *# # ** * NS LSD - 17.4 12.0 - Arrangement 1,5:1 31.5 41.0 50.5 2.4 3:1 24.1 36.9 47.5 4.6 3:1, V 25.6 32.6 43.2 3.8 F-test NS NS NS NS LSD - - - -
NS = non significant, *** differences within a subkolom not significant or significant at P < 0.05 or 0.001 respectively.
Table 13. Production of fruit with more than 33 % red colour (tonnes/ha. Wilhelminadorp, 1994).
Jonagold Fiesta Trees/ha Arrangement (Average for arrangements)
1,5:1 3:1 3:1 V 3.000 58.6 43.6 48.7 29.8 6.000 60.6 49.3 45.9 42.1 10.000 67.7 37.0 39.0 49.7 20.000 29.9 38.4 50.9 37.5 F-test (interaction) * ** * LSD 19.5 7.2
*, *** differences between a subcolomn significant at P < 0.05, or 0.001 respectively.
22 percentage goodqualit y Elstar 1994
70-85m m IVU
80- •
• 60- • • H • • 40- • • •
• • • 20- • • •
0 20 40 60 80 100 tonnastota l
Figure 3. Production of fruit 70-85 mm as percentage of total production (Elstar).
For Jonagold, the production of well-coloured red fruit (more than 33 % red) was similar for all densities in 1994, with the exception of the 2:1 arrangements at 20,000 trees per' ha. Here, the production of well-coloured fruit was markedly lower than for all other densities (Table 13). The production of red Fiesta fruit increased with density, although it was lower for 20,000 than for 10,000 trees per ha. Arrangement had no effect on red colour of Fiesta, but the 1,5:1 systems of Jonagold produced more red- coloured fruit than 3:1 designs, with the exception of the highest density. To conclude, total production increased at light interception values between 60 and 80 %. However, the production of high-quality fruit did not increase as much as total production, and at light interception values passing 80 %, quality could be reduced dramatically.
Planting systems with pear
Wilhelminadorp
In spring 1988, a trial on density and planting systems with Conference pear was planted at Wilhelminadorp. Trees started to produce fruit from the third year after planting. In 1994, the production increased from 56 tonnes at 2000 trees per ha to 65
23 tonnes at 4000 (Table 14). Fruits were smaller at higher densities. In 1994, mean fruit
Table 14. Production (tonnes/ha total and per size class) Conference, Wilhelminadorp, 1994.
Total Size class (mm) 1994 45-55 55-65 65-75 >7 5
Trees/ha 2000 56.3 5.1 38.8 12.4 0.1 2500 60.6 7.6 43.0 10.0 0.1 3000 62.2 6.2 44.5 11.4 0.1 3500 63.9 7.9 46.0 10.0 0.0 4000 65.1 9.2 47.0 9.0 0.1 single row 60.9 7.2 42.9 10.7 0.1 bed 62.4 7.1 44.8 10.4 0.1 weight was only 169 g and 70 % of the fruit was graded between 55 and 65 mm. Only 12 tonnes per ha was, larger than 65 mm at the lowest density, and this figure was even less for higher densities. The planting system did not affect production or fruit weight. Average dry-matter content of the fruit was 15 %; there were no differences between densities or systems. The content of K and Ca was similar for all treatments (127 mg K and 6 mg Ca per 100 g fresh weight). Fruit firmness was 6,25 kg immediately after harvest.
Table 15. Cumulative production and mean fruit weight (1989-1994), Conference at Geldermalsen (G), Horst (H) and Zeewolde (Z).
Tonnes/ha Fruit weight (g) G H Z G H Z
Trees per ha 2000 112 145 185 206 176 176 2500 125 149 193 204 173 176 3000 131 167 202 201 171 171 3500 152 190 220 199 172 170 4000 189 185 219 194 165 169 single row 123 165 200 201 165 165 3-row bed 167 196 173 174 5-row bed 119 170 209 176 V-system 183 216 192 178 mean 142 167 204 201 171 181
24 Light interception was 51 % at bloom, averaged for all treatments, and increased by 2- 3 % per week up to 75 % in the middle of August. Higher densities intercepted more light than lower densities. Finally, systems with 2000 trees per ha intercepted 70 % light and those with 4000 trees intercepted 81 %, averaged for both planting systems. The higher light interception led to more production, but not to a higher production of good-sized fruit. Multi-row systems intercepted 10 % more light than single rows. This did not lead to a higher production, probably because of the higher amount of shade in the multi-row systems. Even at the lowest density, bed systems already intercepted more than 70 % of light.
Geldermalsen, Horst, Zeewolde
In spring 1988, single rows were planted at similar densities as mentioned above, and were compared with North-Holland three-row beds, five-row beds with walking paths, and V-systems at three locations. Per location, three of the four planting systems were studied. Cumulative production increased with density (Table 15). Differences between single rows and multi-row systems were small, but V-systems produced considerably more than upright trees, particularly at Geldermalsen. As at Wilhelminadorp, fruit weight was 10 g lower at 4000 trees per ha than at 2000. The high production of the V- systems at Geldermalsen also led to a reduction of 10 g in fruit weight. Accumulated over all years, Geldermalsen produced 15 % less than Horst and 30 % less than Zeewolde. The fruit size was, however, better. The high production level at Horst and Zeewolde was associated with a mean fruit weight of only 170 g.
The content of dry matter, K and Ca of the fruit, analyzed for Horst and Zeewolde in 1994, was comparable to Wilhelminadorp. Averaged for all treatments, there was 7 and 8 mg Ca, and 123 and 167 mg K per 100 g fresh weight at Horst and Zeewolde, respectively. No effect of treatments was observed. Sugar content, measured only for fruit of Zeewolde, was similar for all densities and varied between 12.5 and 12.9 mg per 100 g. Fruit firmness (Zeewolde) was 4.5 kg on average.
Light measurements with Elstar on commercial fruit holdings
Between 1991 and 1994, light measurements have been performed on commercial holdings in various planting systems and with a number of varieties. In 1994, only systems with Elstar were studied from the third year after planting. Most trees were planted on M.9 rootstock. Some systems on P22 or M.27 did not show marked differences in light interception or production, compared to those on M.9. Light inter ception in the third year was observed to be as high as that of later years. There was a small effect of density on light interception. On average, systems with less than 3500 trees per ha intercepted 64 % light, whereas those with more than 7000 trees intercepted 69 %. Consequently, systems with less than 3500 and more than 7000 trees per ha produced 41 and 54 tonnes per ha, respectively. However, systems with a density between 3500 and 7000 trees per ha intercepted only 60 % of light and produced 34 tonnes per ha. The production of good-quality fruit was about the same for all densities: 12, 11, and 13 tonnes per ha for systems with less than 3500, 3500 to 7000, and more than 7000 trees per ha, respectively. Averaged for all systems, total production varied between 16 and 80 tonnes per ha. Only 27 % of the fruit had more than 33 % red colour. There
25 was no clear relationship between total production and the production of well-coloured fruit. The variation between total production and production of well-sized fruit (70-85 mm) was large (Fig. 3). However, the production of well-sized fruit was smaller for systems producing more than 60 tonnes per ha than for those producing between 40 and 60 tonnes.
Evaluation of chemical thinners
S.J. Wertheim and J.M.T. Balkhoven-Baart
With financial aid from the chemical company Luxan B.V. at Eist eight trials with chemical thinners were carried out in 1994, one on pear and seven on apple. Some new chemicals were compared with standards such as carbaryl, NAAm (Amid Thin), and with no thinning and hand thinning. Trials were made with Conference pear, and with the apple cultivars Cox's Orange Pippin, Elstar (three trials), Golden Delicious, Jonagold, and Red Boskoop. New compounds involved were the flower thinners Lex 9476, D4083, Atoclair, and Neudosan amd the fruitlet thinner D4017. Names of active ingredients are omitted here, because it is illegal to use them in the case of chemicals that have not yet been approved for practical use. Per compound three concentrations were included. All flower thinners caused some degree of burning of the petals; with Conference this only happened with Atoclair and with apple happened especially with Atoclair and D4083. In all cultivars Atoclair had a negative effect on the leaves. Later it appeared that the Atoclair formulation used was not the correct one. The highest concentration of D4083 and in one case of Lex 9476 harmed the leaves. Fruit russeting was also induced by most new compounds, but in the case of D4017 this might have been caused by the wetting agent involved (Luxan H). In the case of Conference only Atoclair thinned. With apple most flower thinners had a thinning effect, except for the lowest concentration of Lex 9476. In general, the higher the concentration the greater the thinning effect. The highest concentration of all compounds caused thinning with all cultivars. Young Elstar trees and mature trees of Cox and Boskoop were thinned too heavily by the highest Atoclair concentration. Similarly with increasing concentrations of the fruit thinner D4017, thinning increased. The highest concentration and in some cases even the middle one, thinned all apple cultivars reasonably well. A final impression will be obtained after the counting of the flower clusters in 1995. The work is being continued in 1995 in an European context with two chemicals: the flower thinner Atoclair (now coded as TD2337-2) and the fruit thinner D4017.
26 Pruning and tree shapes
J.M.T. Balkhoven-Baart
Root-pruning
Apple
In the spring of 1990, a root-pruning trial was started in the regional experimental garden at Numansdorp. Cultivars involved were Elstar and Red Boskoop, both on M.9 rootstock, planted at 3.25 x 1.50 m. The aim was to investigate the effect of mechanical root-pruning or hoeing on tree behaviour. Trees were then in their fourth leaf at the start of the trial. The trees had been planted on fresh land and were fertigated from planting onward. Two root-pruning times were involved: root pruning in May (at the end of flowering) or in June (after June drop); and three hoeing treatments were involved (four times (weekly or two-weekly) or eight times (weekly), from the end of flowering onward). Untreated trees served as controls. The hoeing treatments were only maintained for the first two years, because they had only marginal effect on growth and hoeing proved very difficult under wet conditions. The root-pruning treatments were carried out for five successive years. In 1990, root-pruning was done on both sides of the tree rows with a circular disc at about 50 cm distance from the trunks to a depth of 30 cm. In 1991 and in later years, this distance was decreased to 40 cm. Table 16 shows the relative growth inhibition of the root-pruning treatments. The figures are based upon shoot length (m) removed with summer (1990, 1993, 1994) or winter pruning (1992) and total shoot growth (1991).
Table 16. Percentage of growth inhibition compared with untreated trees in root- pruning trial 083-Nu900136
Treatment 1990 1991 1992 1993 1994
Elstar May 24 46 45 58 56 June 14 38 33 35 53 Red Boskoop May 22 50 52 58 63 June 4 49 38 18 38
Generally, the effect on growth increased over the years and treatment in May had more effect than root pruning in June. Tree volume measured in the spring of 1994 indicated that the annual May treatment gave the smallest trees and at the end of that year some trees had even become too small. The trees root-pruned in June looked more vital. Untreated trees grew too vigorously. The production of the trees was good in spite of their vigour (Table 17). Root-pruning raised productivity per unit of tree volume. Reduced vigour and increased fertility hampered fruit growth. This was most clearly visible with Elstar and after root-pruning in May. This negative effect on fruit size was present especially in the last two years. In
27 1994 this was probably aggravated by the warm and dry summer. Figure 4 shows the fruit size of Elstar in 1994. In that year a shift of about 5 kg per tree occurred from the 70-80 mm to the 65-70 mm size class. With large-fruited triploid Red Boskoop the effects on fruit size were negligible, although productivity per unit of tree volume was increased.
Table 17. Results of root-pruning on productivity and fruit size in root-pruning trial 083-Nu900136
Treatment Kg/ Fruits/ Fruit Fruits/ Tree tree tree weight m3 tree volume 3 (g) volume (m ) 1990-1994 Spring 1994
Elstar Control 135 805 a 175 554 a 1.48 a May 123 789 a 162 762 a 1.10b June 125 757 a 167 612 a 1.28 ab LSD005 NS NS 0.22 Sign. * *
Red Boskoop Control 157 625 a 269 381 x 1.67 x May 153 653 a 255 572 z 1.22 y June 154 633 a 267 478 y 1.33 y LSD0.0B NS 93 0.19 Sign. * ** *
Values per cultivar in the same column followed by the same letter(s) do not differ significantly (P = 0.05); NS = non-significant; *, ** = differences between a subcolomn significant at P < 0.05 or 0.001 respectively
In 1993, in another trial in Numansdorp, the effect of root-pruning close to the tree rows was investigated. Similar trees of Elstar and Red Boskoop on M.9 as mentioned earlier were available for this experiment. Root-pruning was done on both sides of the rows at a distance of 40 cm with an oblique root-pruning knife at an angle of 20° to a depth of 40 cm. Treatments involved were a single root-pruning after harvest 1992 and two root-prunings after harvest 1992 and again in March 1993. Both regimes inhibited growth completely. Production and fruit growth were negatively affected. With Elstar the production from treated trees was 10 kg lower than from untreated ones. This was mainly caused by the smaller fruit on treated trees (117 g after autumn pruning and 127 g after autumn plus spring pruning) as compared to untreated trees (151 g). In 1994, treated Elstar trees still lagged behind in production (5 kg) compared with untreated ones. With Red Boskoop treated trees also gave 5 kg less than untreated ones, both in 1993 and 1994. In 1993, individual fruit weight was 261 g for untreated and 216 g and 212 g for the single autumn treatment and the autumn plus spring treatment respectively. In 1994, also, fruit size was smaller after root-pruning. The results indicate that root-pruning carried out too close to the trunks can be very detrimental.
28 25 20 15 10 No root pruning May June •• 55-65 üü 65-70 70-80 Y///À >80 Figure 4. Fruit size calibration on Elstar in 1994 in root pruning experiment 083- NU900136. Pear In 1990, a trial was started in the regional experimental garden at Numansdorp with the pear cultivars Beurré Hardy, Conference, and Doyenné du Comice planted in the spring of 1987 at 3.00 x 1.25 m to investigate the effects of various times of root pruning (see Table 18). Untreated and CCC-treated trees served as controls. In 1990, mechanical root-pruning was imitated with a spade at 50 cm from the trunks to a depth of 30 cm. In that year no growth inhibition could be measured and therefore in 1992 the distance was reduced to 40 cm from the trunks. From then on root-pruning was done mechanically. In 1992 again, growth was not affected. For that reason, a further change was made in 1993 and root-pruning was carried out 30 cm from the trunks to a depth of 40 cm with an oblique knife (angle 20°). After digging out some trees it appeared that vertical root pruning could not have been effective, because most roots grew downward at a distance of about 20 cm from the trunks. So, vertical root-pruning could only have removed some smaller roots, which explains the lack of any effect on growth. In 1994, oblique root-pruning was repeated. Growth reduction was most apparent after pruning in October, October plus March or in October plus May. If root- 29 pruning was carried out in October after a preceding spring treatment growth was not reduced. The reason for this difference is not clear. It seems that root-pruning in October 1992 has been the most effective treatment with regard to growth control. Table 18. Effects of various treatments onth e production of three pear cultivars in trial 083-NU9312 Treatment Number Kg/tree 1993 - 1994 Kg/tree 1994 root- Conference Doyenné du Beurré > 65 mm prunings Comice Hardy Conference Control 0 38 31 26 10.8 CCC 0 45 35 35 14.5 October 2 38 33 29 15.9 March 2 37 33 28 12.4 Oct+ March 4 37 27 27 12.6 Oct+ May 4 41 33 36 14.5 March+ Oc t 3 38 31 26 14.0 May+ Oc t 3 43 25 33 12.5 Table 19. Effects of various treatments on fertility of three pear cultivars in trial 083-NU9312 Treatment Number Fruits/m3 tree volume 1993 - 1994 root- prunings Conference Doyenné Beurré Average du Comice Hardy all cvs. Control 0 106 a 80 a 88 a 97 a CCC 0 159 a 76 a 121 ab 129 cd October 2 142 a 96 a 119 ab 125 cd March 2 144 a 67 a 122 ab 119 abed May 2 116a 82 a 110 ab 106 abc Oct+ March 4 123 a 95 a 91 a 103 abc Oct+ May 4 155 a 93 a 142 b 136 d March+ Oc t 3 118a 73 a 81a 98 a May+ Oc t 3 119a 69 a 108 ab 104 ab LSD005 NS NS 34 24 Sign. • * Values in one colomn followed by the same letter(s) do not differ significantly (P = 0.05); NS = non-significant; * = differences between a subcolomn significant at P < 0.05 30 Trees treated annually with CCC had the highest production. Root-pruning increased production or had no effect. With Conference a higher production of large fruit resulted with all treatments. CCC and two root-pruning regimes (October, October + May) increased fruit production per unit of tree volume (Table 19). However, this was only significantly so for Beurré Hardy and, more important, for all three cultivars taken together. Alas, the trial had to be ended prematurely, because the garden was closed in the beginning of 1995 for financial reasons. Fruit firmness after root-pruning In various root-pruning trials carried out in 1993 and 1994, with both apple and pear, fruit firmness measurements were made with an Instron penetrometer. Often it appeared that after root-pruning fruit firmness was lower compared to the controls. However, a relationship was detected between fruit number per tree and firmness (Fig. 5). So, probably the lower firmness after root-pruning is an indirect result. The effect of fruit number on firmness was confirmed in a trial with Jonagold in the experimental garden at Geldermalsen. Here, root-pruning was combined with some chemical-thinning treatments and as a result large differences in fruit numbers per tree arose. After root- pruning in March (whether or not combined with chemical thinning) fruit numbers were higher than after root-pruning in August or in non-root-pruned trees. Within the same size class firmness decreased by 0.4 kg/cm2 with an increase of 50 apples per tree. The same was true in another trial with Conference pear, a decrease of 0.6 kg/cm2 with an increase of 50 fruits per tree. In contrast to these findings is the increase in fruit firmness in the before-mentioned trial 083 Nu 90.0.136, where Elstar fruits from root- pruning treatments were firmer than those of the same size class from control trees. Here, no differences in fruit number occurred. So, more information is needed to draw firm conclusions on fruit firmness after root-pruning. A possible explanation for firmer fruits with lower fruit numbers might be that more cell divisions occur, because of the lower level of competition. Growth control with pear CCC-trial In the spring of 1988, a trial was started in the experimental garden at Numansdorp combining two tree shapes with four chlormequat (CCC) treatments (Table 20). The aim was to know what would happen if CC-treatments were stopped after some years. Test cultivars were Conference and Doyenné du Comice, both on Quince MC rootstock. The trees were planted in a three-row system at a distance of 3.00 + (2 x 0.90) x 1.75 m. The tree shapes were a normal slender spindle and a North-Holland spindle. The main difference between the two shapes was that with the latter all side wood was regularly bent horizontally. For the CCC treatments the aim was to investigate for how many years use of a growth retardant is really necessary. From the second year onward twice 0.25 % of a 40 % CCC formulation was applied. The first treatment was sprayed shortly after flowering, the second one 10 to 14 days later. The treatments lasted three, four or five years (Table 20). 31 Fruitflesh firmness (kg/cm2) 6.50 = + 6.00 • 5.50 5.00 4.50 A rvs^^ ~ i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i A i i i i i i i 4.00 40 60 80 100 120 140 160 180 200 Fruits per tree + No root A March • August pruning Figure 5. Firmness of fruit in one calibration class is affected by the fruit number per tree (Jonagold 083-GE93010). Table 20. Production and growth in trial 083-NU8818 Treatment Kg/tree 1989 - 1994 Increase trunk circumference (cm) CCC Conference Doyenné spring 1988 to spring 1994 du Cornice Conference Doyenné duComic e Slender spindle 1989-'91 77 a 49 a 14.2 a 16.7 a 1989-'92 63 a 48 a 13.5 a 16.5 a 1989-'93 75 a 51 a 14.0 a 17.2 a 1989-'94 71 a 50 a 13.2 a 16.1 a North-Holland spindle 1989-'91 67 a 48 a 15.2 a 16.4 a 1989-'92 75 a 49 a 14.8 a 17.0 a 1989-'93 77 a 51 a 14.9 a 16.9 a 1989-'94 71 a 48 a 14.3 a 17.4 a Values in one column followed by the same letter(s) do not differ significantly (P= 0.05) 32 Abandoning CCC spraying had no negative effect on production and little effect on growth as expressed as an increase in trunk circumference. This was true for both tree shapes, which did not differ much in behaviour. However, ceasing spraying with CCC had a great stimulating effect on shoot growth. No effect was seen in 1992, but by 1993, the effect was clearly visable, although production was good in that year. For example, Conference trees treated constantly with CCC had 15 m or 16 m total shoot length per tree in 1993. Trees that received CCC until 1991 had 26 m and 31 m and trees that were sprayed until 1992 grew 18 and 25 m respectively. So, growers who terminate their annual CCC programme may have to face an unexpected increase in growth vigour. Combination of growth controlmeasures In 1994, a trial was started on young pear trees of Conference and Doyenné du Comice, both on Quince MC rootstock, in the experimental garden in Numansdorp, wherein some growth-control measures were applied separately or combined. The measures were: root-pruning, use of chlormequat (CCC), ethephon or NAA as growth retardants. Unfortunately, the trial had to be ended prematurely as a result of the closing of the unit for financial reasons. Therefore no conclusions can be drawn from this experiment. A similar trial has been started in 1995 in Wilhelminadorp. Black skin discoloration in pear S.J. Wertheim Effect of gibberellins In 1994 a trial was set up to investigate the effect of gibberellins (GA) on the occurren ce of black skin discolorations in the cooking pear cultivar Gieser Wildeman. Six GA treatments were compared with an untreated control with five reps of one tree. One treatment received four sprays of 10 ppm GA3 every 10 days from the end of flowe ring. A second treatment received 10 ppm GA4+7 on the same dates. Two other treatments commenced eight weeks after flowering with four sprays of 10 ppm GA3 and of GA4+7 every 10 days. Finally, two treatments received both the early and the late series of both GAs. The GA treatments were meant to reduce the disorder, which it was assumed might be a form of skin russeting that arises early, late or both. None of the treatments had a significant effect on the black skin disorder. Place of the discoloration Grading of the fruit from the above-mentioned experiment revealed that the discolorati on occurred mostly on the cheek of the fruit (81 % of the damaged fruit), and only seldom elsewhere (1 % on the nose end and 1 % on the stalk end of the fruit). In 18 % discolorations occurred on all three places. The black spots mostly occurred on the shadow side of fruit (47 %) or on the transition of the shadow and light side (28 %) and hardly at all only at the blush side (3 %). In 22 % of the fruit black discoloration ocurred all round. When the fruit colour changed to yellow during storage the black spots remained green for longer. Apparently, chlorophyll is disappearing more slowly 33 Relation with cropping level All 35 trees of the before-mentioned trial were graded separately for the occurrence of black skin spots. Five classes were distinguished: no, light, moderate, severe, and very severe occurrence. By multiplying the percentages of fruit in these five classes with an increasing figure (0, 3, 5, 7, and 9) and adding the figures, one index arose that summarizes the grading per tree. The higher the index the more severe the disorder. Figure 6 shows that with increasing fruit number less problems with black spots occurred. The same was found after grading fruit from trees of Gieser Wildeman from other trials. Fruit analysis The pears of the Gieser Wildeman trial mentioned earlier, were analysed for various minerals in three different ways. Each analysis was made with five comparable trees and 15 fruits per tree. The three comparisons were: -sound fruit from trees that cropped well or lightly -fruit with and without black spots from trees that had a reasonable production -skin from black or sound parts of the same fruit from trees that had a light crop Table 1 summarizes the results and it appears, that -sound fruit from light cropping trees had a lower calcium content and a higher content of other minerals, a higher K/Ca ratio and a higher percentage dry matter -black pears had a lower calcium content than sound fruit, but a higher content of other minerals, a higher percentage of dry matter, and a higher K/Ca ratio -the black skin parts contained less calcium, nitrogen, and boron, but had higher contents of other minerals and a higher K/Ca ratio The question is whether these differences are the cause or consequence of the disorder. This will be further investigated in athinnin g trial in 1995. Table 21. Results fruit analysis Gieser Wildeman 1994 Feature 168 72 130 fruits/tr 82 fruits/tr fruits/tree sound black sound black fruit fruit skin skin g/fruit 91 101 104 94 101 101 % dry matter 17.2 19.1 17.3 18.2 22.3 22.3 Ca* 7.78 7.39 7.64 6.30 10.73 9.58 K* 155 184 176 194 265 279 Mg* 7.45 8.37 7.74 7.78 9.59 9.82 N* 69.9 80.7 73.6 74.3 105.9 100.9 P* 14.2 17.1 14.9 16.3 24.3 25.3 B* 8.0 8.7 11.2 15.0 13.9 9.3 K/Ca 19.8 25.0 23.4 31.2 25.3 29.8 in mg/g fresh weight 34 BlaofctklnIndo e 600- • •V * 600- 400- • • 300- • . • • • 200- ^^^ • • • 100- 0- 1 1 i i • 60 76 100 126 160 176 200 226 260 Rlllts/lfM Figure 6. Relation between cropping and black skin discoloration 35 Evaluation of Top Fruit Cultivars Cultivar testing with apple H. Kemp, P.D. Goddrie, and M.CA. van Dieren Cultivar trials in Wilhelminadorp In the spring of 1994, 80 new cultivars were included in the test blocks, the majority originating from breeding work carried out in Germany, Switzerland or the USA. More than half of the cultivars planted, are claimed to be resistant against apple scab. All cultivars were planted both in a parcel with a standard fungicide-spraying programme and in a block without such a programme. The common rootstock is M.9. In the winter of 1994/'95, 92 cultivars were removed from the collection. The main reason for rejection was insufficient eating quality, but there were some other reasons, too. More details are given in Table 22, where cultivars are arranged in alphabetical order. Table 22. Data of apple cultivars removed in winter 1994/'95 (* claimed to scab- resistant) Cultivar Origin Plant Characte- Other year ristics eating qual. 8C-5-62 Canada 1989 fg 8L-13-13 Canada 1991 m unattractive fruit 8M-2-8 Canada 1991 m 8NE-7-72 Canada 1993 m unattractive fruit 9P-15-30 Canada 1991 m 11W-19-18 Canada 1993 fg bitter pit A92/23" England 1993 m rather unattractive fruit A235/1] England 1993 fg much russeting Baujade* France 1993 m very late ripening Beemstervroeg* Netherlands 1993 p-m low susceptibility to scab BM 46591 Sweden 1992 m acid, early ripening BM 47671 Sweden 1992 p-m unattractive fruit BM 50717 Sweden 1992 m early ripening, short fruit stalk BM 51880 Sweden 1992 m early ripening BM 54859 Sweden 1992 fg 1 early ripening Celica (Welbo) Netherlands 1989 fg more blush than Rode Boskoop 'Schmitz Hübsch' Co-op 27' USA 1991 m Co-op 28* USA 1991 m soft scald Co-op 29* USA 1991 m russeting, mildew, biennial bearing Co-op 31" USA 1991 m russeting 36 CPRO 78123-5 Netherlands 1992 (f) g bitter pit, moderate producti on CPRO 78129-30 Netherlands 1991 m soft scald CPRO 79032-3 Netherlands 1991 fg soft scald CPRO 80015-47" Netherlands 1992 fg russeting CPRO 80101-104 Netherlands 1990 fg somewhat sweet taste CPRO 80116-14 Netherlands 1991 m CPRO 81015-33 Netherlands 1990 fg productive, somewhat wate ry, fleshy fruit stalk CPRO 81027-3 Netherlands 1993 f g slack wood CPRO 82002-6 Netherlands 1991 fg slack wood CPRO 82003-57 Netherlands 1991 fg rather acid, russeting CPRO 82050-32 Netherlands 1991 m low production, rather small fruit Dayton* USA 1991 m Delprivale France 1991 m low production, early ripening E55/40 England 1993 m acid E55/68 England 1993 m core rot E55/75 ^ England 1993 m Generös* Rumania 1993 m Gloria Germany 1993 fg core rot G.D. Rozendaal Netherlands 1993 fg Golden Delicious mutant with unattractive blush Graf Ezzo Germany 1993 fg H 1146 Germany 1993 fg acid, unattractive, small fruit H 1152 Germany 1993 m core rot H 1165 Germany 1993 (f)g water core H 1166 Germany 1993 m stalk-end cracking H 1171 Germany 1993 fg H 1177 Germany 1993 fg long fruit stalk H 1181 Germany 1993 m unattractive fruit H 1187 Germany 1993 fg large stalk-end cracks H 1195 Germany 1993 p-m stalk-end russeting,cracking H 1200 Germany 1993 p-m H 1205 Germany 1993 fg rather much russeting H 1209 Germany 1993 p m rather unattractive fruit H 1210 Germany 1993 m H 1217 Germany 1993 m acid, short fruit stalk H 1237 Germany 1993 m long fruit stalk, attractive fruit Hongaru Hungary 1993 m resembles Mutsu Joseph Musch* Belgium 1994 P acid, unattractive fruit Karmijn de Sonna- ville 'Kuin' Netherlands 1991 g more blush than standard Kogetsu Japan 1992 m L36 Germany 1993 m core rot L41 Germany 1993 m acid L45 Germany 1993 p-m 37 Margol Germany 1991 (f) g low/moderately susceptible to scab and powdery mildew Merlyn* Belgium 1993 m not scab-resistant (Table 23) NY 617 USA 1991 fg unattractive fruit NY 619 USA 1991 fg NY 678 USA 1991 fg off-flavour, short fruit stalk Otava* Czech Rep. 1992 p-m magnesium deficiency Pi-A-24,5 Germany 1992 P unattractive fruit, water core Pilot Germany 1989 m late ripening, firm, bumpy fruit Pinova Germany 1989 fg somewhat insipid taste, late ripening, good cropper and keeper Pionier" Rumania 1993 P soft scald, short fruit stalk Primicia* Brasil 1991 m very vigorous, soft scald, low chilling requirement Realka* Germany 1992 P scald, unattractive fruit Reanda" Germany 1994 P bitter pit, unattractive fruit Red Aroma Sweden 1992 m chimaeras, short fruit stalk Reka* Germany 1992 m off-flavour, unattractive fruit (shape) Relinda* Germany 1992 m acid, bitter pit, russeting, cracking Renora* Germany 1994 p-m acid Rewena* Germany 1992 p-m acid, long fruit stalk Rode Boskoop Germany 1989 fg more blush than Rode Bos SHKL1 koop 'Schmitz Hübsch' Rode Boskoop Netherlands 1992 fg more blush than Rode Bos van der Vliet1 koop 'Schmitz Hübsch' Romus-1 * Rumania 1993 fg early ripening, small fruit Romus-3* Rumania 1993 m early ripening, small fruit Rosana* Czech Rep. 1992 m off-flavour Rubinola* Czech Rep. 1992 m bare wood, small fruit, long fruit stalk Schone van Germany 1989 fg spur type, good productivity Boskoop SP1 Vanda* Czech Rep. 1992 fg very sensitive to bitter pit, soft fruit Vegi Cox's O.P. Belgium 1992 g practically identical to T12 Voinea* Rumania 1993 p-m Willams Pride* USA 1991 fg rather small fruit X 3177* France 1989 m long fruit stalk 1 Boskoop mutants included in national trial 069-WÎ9502 planted in Horst and Wilhelmi nadorp. # p = poor, m = moderate, f g = fairly good, g = good. 38 During the summer of 1994, the cultivars occurring in a block without fungicide application were judged for the presence of scab (on fruits at harvest) and mildew (both on shoots and leaves in May and July). Table 23 summarizes the main results. Table 23. Rating for occurrence of scab and powdery mildew in 1994 Cultivar Year without Fruit Leaf/shoot fungicides scab* mildew * Non resistant cultivars Alkmene 5 3 5 Cox's Orange Pippin 5 4 3 CPRO 81003-49 4 1 0 Discovery 5 2 1 Elise 5 5 2 Elstar 5 3 5 Gala (Regal Prince) 4 5 6 Golden Delicious 5 8 2 Jonagold 2 4 7 Red Boskoop Schmitz H 5 4 5 Disease-resistant cultivars CPRO 78038-9 5 0 8 CPRO 84015-17 2 0 1 Ecolette (CPRO 78039-18) 5 0 2 Enterprise (Co-op 30) 4 0 4 Fiorina 5 0 5 Merlyn 2 1 2 Otava 3 0 4 Prima 5 0 1 Priscilla 5 0 6 Rosana 3 0 2 SA 15/4 2 0 1 Vanda 3 0 4 * 0 = none; 1 = very little to 9 = excessive occurrence In 1994, the scab-resistant cultivars showed hardly any scab. Merlyn showed most symptoms. On the other scab resistant cultivars, occasionally a scab spot was found. No scab and little mildew was observed with CPRO 84015-17 (Elstar x Prima). Fruit of this selection tasted well, but fruit appearance was a bit disappointing. As for the non- resistant cultivars, CPRO 81003-49 showed very little scab. This is a hybrid from Discovery x James Grieve, and also the parent Discovery was classed favourably. In the winter of 1994/'95, five taste tests were carried out with a panel of about 30 people from the Research Station. Fruits of all cultivars involved were stored until 4 days before the test at 3 °C and after that kept at room temperature. Table 24 shows the outcome of these tests. 39 Table 24. Taste scores apple cultivars winter 1994/'95 Cultivar Score 09/11 25/11 28/11 09/12 07/02 Baujade . 4.3 d Co-op 29 - 6.0 a CPRO 78038-9 6.3 b 6.5 a CPRO 80015-47 4.8 c 4.8 c Delblush - 6.3 a 6.3 a 5.5 bc Ecolette - - 5.5 a - Elise - - - 6.5 a Elstar 7.1 a 6.9 a Enterprise - . 6.0 a 5.6 bc Golden Delicious - 5.8 a 5.6 a - Jonagold - - - 6.0 ab Margol - 5.9 b Pinova - 5.8 a - 5.1 c Reka 4.6 c Rene - 4.9 b - - Retina 3.6 d Rewena - 4.0 c _ _ SA 15/4 - 4.2 c scale: 1 = very poor to 9 = excellent. Values in one column followed by the same letter(s) do not differ significantly (P = 0.05). Reka and Retina were rated as (too) soft by some of the panel and CPRO 80015-47 as firm and acid (9 November). On November 25, CPRO 80015-47 was still rated as acid. At that time SA 15/4 was already soft and partly broken down. On November 28, Delblush was very firm, Pinova firm but flat and Golden Delicious somewhat soft. Rene was too soft by then and Rewena (too) acid. On December 9, Co-op 29, Delblush and Enterprise were all considered to be (rather) firm. Ecolette was rated as acid and Golden Delicious as too softly. On February 7, Baujade was found to be somewhat acid and tough, Delblush firm and Elise, Enterprise and Jonagold (too) soft. Pinova was rated as firm and flat sweet. Margol tastes rather well, but can not be considered as a valuable addition. It was noteworthy that the (too) soft Elise and Jonagold were rated higher than the firmer Delblush and Pinova. Apparently, the somewhat peculiar taste of Delblush was not highly valued by all panel members. However, fruit appearance, storability and shelf life of Delblush were impressive. As in former years, the taste of Ecolette was rated fairly well. This cultivar will be introduced in August 1995. In spite of their scab-resistance, CPRO 80015-47, Reka, Rene, Retina, Rewena, and SA 15/4 are not considered as valuable additions to the apple assortment. Baujade, a scab- resistant cultivar with Granny Smith-type fruit, tasted poor to moderate, partly because of too late ripening. For the time being, within the group of scab-resistant cultivars, CPRO 78038-9 and Enterprise seem to be the most valuable ones. 40 Clone trials in Wilhelminadorp Cox's Orange Pippin The clone trial planted in the spring of 1991 with trees on M.9 cropped for the third time in 1994 (Table 25). Differences in production may in part be due to differences in virus status, but the virus-free clones Van Vliet 2 and Korallo still lagged behind in productivity. Clones De Bruyn, Van Vliet 2 and 4, T1088, T12, Kummer B396, and both Queen Cox types have bright (orange-)red fruit, whereas Van Vliet M., Steyn, and Zwanenburg deliver dark-red fruit. Heidens, Van der Ploeg, Van der Rijdt, Buysens, Crimson Cox and Korallo have bright to dark-red apples. This holds as well for In 't Table 25. Results clone trial Cox 's Orange Pippin (069-WI9102) Clone 1992 to 1994 1994 Kg/ Fruit % fruit Trunk Tree tree y weight > 70 mm circ. volume 3 m (g) (cm) (m ) De Bruyn 21 34 161 38 11.3 0.63 Heidens 25 42 181 69 12.2 0.61 In 't Veld 26 41 171 52 12.0 0.68 Van der Ploeg 24 41 166 42 11.2 0.62 Van der Rijdt 31 43 172 53 13.7 0.74 Buysens 23 35 162 48 11.8 0.70 Vroemen 25 36 158 52 11.8 0.72 Flikweert 28 31 183 71 13.5 0.93 Roelse 31 42 172 50 13.1 0.78 Van Vliet M. 23 39 161 43 11.3 0.61 Van Vliet 2 16 18 223 92 14.5 0.92 Van Vliet 4 34 43 189 76 13.7 0.81 Steyn 33 45 163 44 13.2 0.78 Zwanenburg" 38 48 164 44 13.6 0.87 Crimson Cox 23 39 159 51 11.6 0.62 T1088 30 38 165 30 12.3 0.84 Korallo 23 28 177 68 12.4 0.82 T12 31 40 164 51 13.3 0.79 Kummer B396 25 37 155 48 12.5 0.71 Queen Cox EMLA 29 36 172 56 13.3 0.81 Queen Cox B293 32 38 183 75 13.4 0.88 planted as two-year-old trees with interstem, all others as one-year-old well-feathered trees. Veld, Vroemen, Flikweert and Roelse, but here the accent is on the bright red side. Of these, Roelse seems the most beautiful (most bright-red), but in 1993 the three others had a higher percentage blush. In September 1994, the leaves of all clones were rated 41 as healthy; this was especially true for Buysens, Roelse, Steyn, Zwanenburg and Korallo. Conclusions on differences between the clones are hard to draw, because of the dissimilar virus status. The preference of the trade tends to go towards the bright orange-red instead of the bright to dark-red Cox fruits. Therefore, clones of Queen Cox (Table 26) might be a better option than the four earlier-mentioned bright to dark-red types. This also holds for the clones, Ruissen and Verschure, that were added to trial 069-WI9206 in the spring of 1992. In the spring of 1992, three trials were planted with various English clones of Queen Cox. Five of these are supposedly self-fertile (clones 7, 13, 14, 18, and 106, although from 13, 14, and 106 this is not quite certain). A reliable self-fertile Cox would diminish the need for pollinizers and increase the certainty of production. A disadvantage could be that when a possibly increased need for thinning is not fulfilled, fruit size and regularity of production might be negatively affected. All clones were planted as heavily feathered one-year-old trees on M.9. The trees of the various clones were of very similar quality, except that the trees of Queen Cox Heines had a few less feathers. All clones cropped well in 1993 and 1994 (Table 26). In September 1994, leaves of all clones looked rather healthy, Clone 7 a bit less so. This clone also lagged behind in production and Table 26. Results Queen Cox clone trial (069-WI9206 and 9207) Clone 1993 to 1994 1994 Kg/ Fruit % fruit Trunk Tree tree 3m ' weight > 70 mm circ. volume 3 (g) (cm) (m ) Heines 16 29 144 42 10.3 0.57 7 17 25 134 11 10.8 0.70 9 19 34 147 48 11.3 0.62 13 18 30 161 60 11.5 0.62 14 19 26 147 47 11.2 0.75 18 18 30 140 33 10.8 0.63 56 20 27 150 50 11.6 0.78 91 19 31 144 46 11.4 0.62 106 18 35 147 50 11.0 0.55 4* 22 30 157 59 11.5 0.77 * Data from trial 9207, other data from 9206 fruit size. Clone 18 had slightly smaller fruit, too. Clones 4 and 13 combined good production with good fruit size. Clones Heines, 9, 14 and 91 had the best fruit appearance (1994). In 1994, in clones 7, 18, 56, 91 and 106 a few trees occurred that entirely or partly yielded standard Cox fruit. In 1994, in all clones more than 90 % of 42 the fruits were blushed for more than 50 % blushed; only Clone 56 was a bit less with 80 %. All clones gave bright-red fruits. Elstar In the springs of 1989 to 1993, 10, 19, 5, 1 and 1 (colour) mutants of Elstar were planted respectively, with in almost all cases, four trees on M.9 per clone. These clones had only been evaluated for fruit appearance. In the winter of 1994, this whole comparison was ended and the main impressions are given in Table 27. With the best types a new trial has been planted in the experimental garden at Zeewolde in the spring of 1995. Mutants that showed (very) many chimaeras were: Vlaar (striped), Bruynzeel I and II, Daamen II, Daliter, De Jager K, Nodop, PFW-lla and -Mb, Stassen, Van der Zalm II, and Van Liere I and II. The mutant Flikweert K showed an upright spur type-like habit. Table 27. Colour grouping Elstar mutants (069-WI89010) Blush Mutant Bright-red with stripes Stassen, Bruynzeel I and III, Daamen If, as standard Elstar" De Jager K and Zw, Rietveld II, Daliter, Jacobs", Van der Plasse*, Flikweert K Bright to dark-red Nodop, Van Kampen with stripes as standard Dark-red with stripes Vlaar, Van der Zalm II as standard Elstar (Almost) uniform Daamen I, Huisman, In 't Groen", Van bright-red Wijk, Van Kaam, Bosman, Bruynzeel If, Flikweert, Heines", PFW-lla and -Mb", Van Liere I and II Uniform bright to dark- Boerekamp, Bougie, Roelofs red (Almost) uniform dark- De Bruin, Kuin, Bel-El ( = Elswout)*, red Daliest, Elnica included in trial 069 Ze 9506 planted in the spring of 1995 in Zeewolde. ** mostly with more blush than standard Elstar. Jonagold In the springs of 1989 to 1993, 12, 21,4 , 2 and 1 (colour) mutants of Jonagold were planted respectively with four trees per mutant on M.9. Evaluation of fruit appearance 43 was the sole purpose of this comparison. The evaluation was finished at the end of 1994 and results are summarized in Table 28. A more extensive trial with various mutants, chosen in 1990, was planted in the spring of 1992 in the experimental gardens of Horst, Numansdorp and Zeewolde (069-WI9201; see below). Clone Groffils showed one tree with bright to dark-red fruit. PFW-II gave only a few apples, that were striped and dark-red to purple, and showed aberrant leaves. Stassen was rather striped. New Jonagold R.N. and Van Weverwijk showed (very) many chimaeras. The mutants 2000, New Jonagold R.N., and Jorayca, had one tree with standard Jonagold fruit. Table 28. Colour grouping Jonagold mutants (069-WI89012) Blush Mutant Bright-red with stripes Ley, Heines, Groffils, Eversdijk III as standard Jonagold" and IV, Glerum, Ruissen, Stassen, Van Weverwijk, Dalijo, Boonen, Fernelmont, Verbruggen, Zweeren (Almost) uniform bright- Van de Bliek, 2000*, Daamen II, red Eversdijk I, Lindenbergh, Waterval, New Jonagold R.N., Verploeg, Schneica B\ Prince Jonagold d'Haemer Uniform bright to dark- Romagold, Eversdijk II,Braun , red Meesters, Jorayca Brown-red Reniers I and II, 4001 (Almost) uniform dark-red Martens I and II, Romagold, Jonagored*, Jonagored HR', Nijsten, PFW-II, Boerekamp included in trial 069-WI9201 in experimental gardens at Horst, Numansdorp, and Zeewolde. " mostly with more blush than the standard Jonagold. Stabilitycolour mutants Elstar In the spring of 1989, a trial (069-WI89011) was planted with two colour mutants of Elstar to evaluate the stability of colour mutations in subsequent generations. From Elshof (Elstar Elshof I), 20 one-year-old trees on M.9 were planted and from Elstar PFW- I, 20 similar trees. From both mutants the next generation was planted in the spring of 1990 (069-WI89011a); all one-year-old maiden trees on M.9: 170 trees (fifth genera tion) of Elshof and 150 trees (fourth generation) of Elstar PFW-I. In the same trial 370 trees (fourth generation) of Red Elstar were planted. Observations from 1990 to 1993 revealed more back mutation in Red Elstar than in Elshof and PFW-I. Back mutation means the re-appearance of standard Elstar fruits. In 1994, within Elshof and PFW-I, also, an increase in back mutation was observed. Red Elstar could not be evaluated in 1994. So, in general there was an increase in back mutation over a period of time. 44 There was also an increase in the rate of back mutation within atree . Stabilitycolour mutants Jonagold In the spring of 1989, a comparison was planted (069-WI89013) with Jonagold colour mutants Novajo and Crowngold. From Novajo, four one-year-old table grafts on M.9 were planted and from Crowngold eight. The trees were the third generation. Propaga ted from the same material, 40 one-year-old Novajo and 80 Crowngold, hence fourth generation, were planted in the spring of 1990 (069-WI89013a). From 1990 to 1994, Novajo showed no signs of back mutation, but with Crowngold two trees showed less intensely coloured fruit, which were almost similar to standard Jonagold in a number of years. For two other trees this was also the case but less so. Both for Elstar and Jonagold, it held that the more the mutant is like the standard, the higher is the rate of back mutation. Clone trials in regional experimental gardens In the spring of 1992, a national trial was planted in three experimental gardens (Horst, Numansdorp, Zeewolde) with 13 colour mutants of Jonagold (069-HO/NU/ZE9201). All trees were raised in a single nursery on M.9 and planted as one-year-old trees on the three sites. The trial was planted in 6 reps (Horst, Zeewolde) or 4 reps (Numansdorp) with 3 to 5 trees per plot respectively. The mutants are given in Table 29, and the first Table 29. Growth data Jonagold colour mutant trial (069-HO/NU/ZE9201) Mutant Trunk Tree Number Average circum volume shoots/ shoot ference (cm (m3) tree length (cm) Spring Autumn Autumn 1992 1994 1994 Average 1992 to 1994 Wilmuta 4.8 8.8 0.75 43 27 Crowngold 4.9 9.4 0.80 46 29 Schneica B 4.8 9.6 0.74 44 29 King 8765 T 4.7 8.9 0.76 45 30 Jonakap 4.7 9.1 0.73 43 28 Decosta 4.7 9.1 0.74 45 29 Jonagored 9614 4.9 9.0 0.71 44 30 Jonagored HR 2458 4.8 8.8 0.74 44 29 Jonabel 4.7 9.3 0.74 42 28 2000 4.8 8.4 0.75 37 27 Novajo 4.8 8.3 0.65 38 26 Jonaveld 4.6 8.6 0.72 37 28 Jomured 4.9 8.3 0.74 41 26 LSD005 NS NS NS 4.7 1.9 Values in one column that differ more than the LSD-values are significantly different. NS = no significant difference. 45 eight listed were probably virus-free, but the last five were not (the material in this trial). There are some synonyms worth mentioning here: Schneica B is Jonica B; Jonakap is Jonagold de Jager I; Decosta is similar to Swillen, DC or Verbeek; Jonabel to Jonagold Van Gelder; Novajo to Jonagold Veulemans; Jonaveld to Jonagold In 't Veld, and Jomured to Jonagold VandePoel. Wilmuta was included for reference purposes and this clone is comparable to standard Jonagold except for the amount of red blush. The trial was ended in Numansdorp in the winter of 1994/'95, because of the closure of this garden. At planting, the trunks did not differ much in size (Table 29) and neither did the number of feathers per tree. The trunk circumference and tree volume were determined at the end of 1994. Table 29 only gives the data for Numans dorp (trunk) together with tree volumes (Zeewolde) and data of shoot measurements made in Zeewolde at the end of 1992, 1993 and 1994. The observed growth differen ces were small. In autumn 1994, the trunks of King 8765 T, Jonagored 9614, Crowngold and Decosta were significantly greater than those of Wilmuta. The same held in Numansdorp and Horst, but not significantly. In none of the gardens did tree volumes of the mutants differ significantly from Wilmuta, but in all cases those of Novajo were the smallest. The first fruits were picked in 1992 in Numansdorp and Zeewolde, and in 1993 and 1994 good productions were obtained at all three sites (Table 30). In Zeewolde and Numansdorp, tree productions from some virus-free mutants were higher than those from Wilmuta, but in Horst this was not so. Production per tree volume did not differ much, except for Jonagored HR 2458 that produced less. The production of most non- virus-free mutants lagged behind that of Wilmuta. Fruit size varied per site, but in all gardens the fruit of the non-virus-free Novajo, Jonaveld and Jomured were the smallest. Table 30. Production data Jonagold colour mutant trial (069-HO/NU/ZE9201) Mutant Production to 1994 Av. fr. weight Kg/tree Kg/m3 (g) 1993-1994 Ho Nu Ze 3 sites Ze Wilmuta 35.8 21.0 31.6 39.1 211 Crowngold 31.1 23.8 35.0 36.3 212 Schneica B 30.8 24.1 34.3 36.2 219 King 8765 T 33.3 19.7 33.8 35.9 212 Jonakap 34.0 23.6 35.0 37.4 203 Decosta 33.5 21.2 35.0 38.8 210 Jonagored 9614 32.9 19.8 32.6 37.5 220 Jonagored HR 2458 27.5 18.1 33.8 34.6 218 Jonabel 31.5 20.4 32.2 36.2 211 2000 28.0 15.3 27.6 31.7 208 Novajo 28.9 15.9 28.3 36.4 195 Jonaveld 30.4 17.5 31.3 36.4 196 Jomured 32.7 15.6 29.9 34.9 201 LSD005 4.0 3.8 2.7 3.9 7.8 Values in one column that differ more than the LSD-values are significantly different 46 In 1994, in all gardens, colour gradings were made. These data, together with weight percentages harvested in the three pickings, give impressions on the amount of colour. Some data of two gardens are given in Table 31. Table31 . Colouring data Jonagold colour mutant trial (069-HO/NU/ZE9201) Mutant Numansdorp 1994 Zeewolde 1994 % kg in pi eking colour index % kg with % blush from picking 1 2 3 1 2 33-50 -75 >75 Wilmuta 32 54 14 500 456 21 52 21 Crowngold 40 49 11 513 478 16 53 27 Schneica B 40 54 6 513 488 13 53 30 King 8765 T 47 48 5 514 492 15 51 31 Jonakap 35 54 12 513 484 15 51 30 Decosta 73 27 0 565 561 3 28 68 Jonagored 9614 80 20 0 584 584 1 15 84 Jonagored HR 66 34 0 577 569 1 21 77 Jonabel 42 54 4 523 522 11 52 36 2000 49 49 2 506 527 12 54 32 Novajo 74 24 1 517 520 11 56 32 Jonaveld 74 26 0 578 585 1 18 81 Jomured 88 12 0 585 587 0 14 85 LSD (005) 10.2 9.3 3.9 15.4 19.5 - - -") Values in one column that differ more than the LSD-values are significantly different. *) Colour index: the higher the more colour. ") Because of statistical transformation no LSD-values given. At all sites, all mutants gave better coloured fruit than Wilmuta. Considering the amount of blush, three colour groups could be distinguished. First, the dark red mutants (Jomured, Jonaveld, Jonagored 9614, Jonagored HR 2458 and Decosta). These mutants clearly had more red blush than the other mutants. Second were the bright red mutants (Wilmuta, Crowngold, Jonakap, Schneica B and King 8765 T) with the least red colour. Third was the intermediate group (Jonabel, Novajo, and 2000). Within the first group Decosta had the least red colour and this mutant was also the least dark red. Within the second group, Crowngold and Jonakap came closest to Wilmuta. So, with Jonabel, King 8765 T, and Schneica B, a somewhat greater step is being made towards a bright red Jonagold with a greater amount of blush. The differences however were small and not always significant. In 1995, colour gradings will be made again, except alas in Numansdorp because this site has been closed. From the most interesting mutants, internal fruit quality, storage potential and shelf life will be assessed as well. Therefore, the above-mentioned conclusions are not final. From earlier work with Jonagold mutants (069 8709) it appeared that with increasing tree age the percentage of fruits with more than 50% 47 blush diminished considerably, especially with the standard-like types and the bright red mutants. This was hardly applicable for the dark red mutants. April 1995, the mutants Crowngold, Jonagored and Schneica (Jonica) have obtained plant breeders' rights, the others have not (yet). This project was alsomade possible with fundsfrom Eurofru. Cultivar testing with pear H.Kemp, P.D. Goddrie and M.C.A. van Dieren Cultivar trials in Wilhelminadorp In the spring of 1993, 12 cultivars were included in the test blocks. Seven of these are fairly early ripening cultivars from Norway and Sweden. Two should have low suscepti bility to pear scab, and one is a bronze-skinned mutant of Conference. Almost all the cultivars are on Quince MC rootstock with an interstem of Beurré Hardy. In spring 1994, 25 new cultivars were added; 19 of these should have low susceptibili ty to fire blight. From 1994 onwards, the pear cultivars have been evaluated with ten trees in a block whith a standard fungicide programme being applied, and five trees in a separate block whith all fungicide sprays being omitted. Here, susceptibility to fungus diseases is being evaluated. In 1994, scab was not found on any of these cultivars. From 1994 onwards, Doyenné du Comice has been used as an interstem for pear instead of Hardy, because in an interstem trial the former gave better fertility to the scion cultivar. In the winter of 1994/'95, 26 cultivars were removed from the trials (Table 32), partly because the oldest pear block had to be abandoned. Given the limited importance of Beurré Hardy and the small differences between the three red-coloured mutants that were planted in 1992, it was decided to grub two of these (Table 32). The third mutant had fruit that was on average 55 % purple-red blushed. Also three other red coloured cultivars were also removed (Table 32), so that in 1995 only six red coloured cultivars and some red mutations remain. Concorde has been tested sufficiently and is now being planted in practice on a limited scale. Given the fact that Concorde has hardly any advantages when compared with Conference, no great increase is expected. After nine years, the tree volume of Concorde was about 10 % smaller than that of Conference, so it is a cultivar of rather low vigour. An application for Plant Breeders' Rights has been submitted for CPRO 69007-36. Possibly, this cultivar can acquire a small place within the pear assortment as a replacement for Clapp's Favourite. Replacement of Triomphe de Vienne is not expected (see also Table 33). The trees of Dolacomi, that are probably virus free, were replanted after twelve years in the autumn of 1994. After that period the tree volume was 20 - 25 % smaller than that of Conference. Tree production was lower, but production per unit of tree volume was about 10 % higher than that of Conference. The first propagati on wood was supplied to English and Dutch nurseries in the summer of 1995. One year (or two years) later, other countries will be able to follow. The NAKB will bring this 48 name-protected cultivar at pay. The application for Plant Breeders' Rights is running. Table 32. Data on pear cultivars from a terminated trial Cultivar Origin Plant Characteristics year 6.30.100* France 1990 good taste, much russeting and cracking Abate Fétef France 1990 poor eating quality, poor compatibility with quince Baurotard* France 1993 low vigour even virus free, poor compatibility with quince, moderate eating quality B.Hardy red A Netherl. 1992 fruit which is too purple coloured B.Hardy red C Netherl. 1992 fruit which is too purple coloured Concorde England 1986 good cropper and keeper, good taste, somewhat crisp Conference Netherl. 1987 30 to 40 % more bronzed than Brons standard Conference Conf. Massouk* Belgium 1990 large fruit, low cropping Conf. Vlaskamp* Netherl. 1990 large fruit, low cropping CPRO 68006- Netherl. 1987 very productive, good taste, late ripening, 123* unattractive fruit, susceptible to fire blight CPRO 69007-36 Netherl. 1987 autumn pear, sufficiently productive, fairly good taste (Table 33), 1 month storage, fire-blight susceptible Delwilmor* France 1990 Fertilia Delbard®, very productive, moderate taste Dolacomi England 1983 compact tree, good cropping, and taste (Jowil®) ^ Hartman* USA 1990 pink red, unattractive fruit, late ripening, rather poor ramification, moderate production, fairly good taste I/9* Yugosl. 1990 dark red fruit, short shelf life, moderate taste K2 07-72*^ France 1990 too large, fairly acid fruit Lombacad* USA 1990 Cascade®, dark red fruit, poor keeper, dry, modera- taste, poor growth with virus P 46/5* England 1990 fairly good taste, rather fair fruit P 83/13" England 1990 moderate taste P 152/8* England 1990 moderately good taste, fair fruit PB 30/6" England 1990 somewhat insipid sweet taste Pierre Corneille* France 1990 productive, with interstem strong vigour, attractive fruit, fairly good taste, susceptible to scald Sierra* USA 1986 leaves light green, little growth, even on interstem (virus infected), fairly good taste Suypeer* Netherl. 1989 cooking pear, somewhat insipid taste, large sound fruit Verdi Netherl. 1987 good taste, attractive fruit, spring-frost sensitive, poor compatibility with quince Zaailing Netherl. 1992 moderate taste, poor shelf life van Liere* *) Not recommended for culture in The Netherlands 49 Dolacomi seems to be very suitable for a culture with small trees (cordons). In 1994, biennialism was observed on trees that had been planted as one-year-old trees on Quince MC in 1992. These trees cropped very well in 1993 and flowered lightly in 1994, but did not crop at all. So, early thinning of young profusely flowering trees seems a necessity. Verdi was introduced in 1994 and in the budding season 55,000 buds were distributed by the NAKB. For taste data see Tables 31 and 32. During the winter of 1994/'95, nine taste-panel tests were held with pears from various cultivars. All fruits used in these tests were stored until six days before the actual tasting began at 1 °C and 21 % oxygen. During the six days before tasting fruits were ripened at 18 °C to 20 °C. Only fruits of Delmoip were kept at room temperature for 8 days with the test in February. Tests where cultivars were compared were carried out by a panel of 30 people, and those where small and large fruits of the same cultivar were compared were made by a panel of 20 people. Table 33 shows some results of a comparison between early ripening cultivars. Table 33. Results of a taste comparison with early-ripening cultivars held in September 1994 (scale: 1 = very poor taste, 9 = exellent taste) Cultivar Score Triomphe de Vienne 6.4 a Delete 5.9 ab CPRO 69007-36 5.7 b Conference Saels II 5.7 b Clapp's Favourite 4.6 c Values followed by the same letter(s) do not differ significantly (P= 0.05) The taste of CPRO 69007-36, a hybrid between Clapp's Favourite and Doyenné du Comice, was given a higher assessment than in a previous test held in October 1993. Apparently, consumption in October is too late for this cultivar. This time taste was better than that of Clapp's Favourite, but not as good as Triomphe de Vienne. Delete or Delbardelice® tasted better than the CPRO number. The same was true in October 1993, but according to a number of panel members the taste was (too) acid. Delete was planted in the spring of 1990 as one-year-old trees on Quince MC rootstock with an interstem. So far, production and fruit size have been insufficient. The taste of the early-ripening Conference mutant called Saels II was considered too flat (see also Table 34). In 1994, eight Conference mutants were under study. Two fruit size mutants cropped insufficiently (Table 32). The vigour of Conference Brons was lower than that of standard Conference and productivity per tree was much lower. However, this mutant is probably virus-free. Conference Saels I and Goud also produced less than the standard. From one fruit-size mutant and one bronze-skinned mutant the data available are still insufficient. In all four mutants the seed numbers per fruit were lower than those of the standard. The very low number of Saels I suggests a different ploidy level. 50 Table 34. Results of tests with Conference mutants (taste test in Decemebr 1994; scale see Table 33) Conference Planting Mean Full Taste type year fruit seeds/ score weight (g) fruit" Brons 1987 205 0.50 7.2a Goud 1990 214 0.43 6.3b Saels I 1990 279 0.07 6.3b Saels II 1990 151 0.87 5.7c Values in one column followed by the same letter do not differ significantly (P = 0.05). * from 30 fruits obtained from open pollination. Former self-pollinations with standard Conference gave full-seed numbers between 0.0 and 2.0; crossings with normal Conference rated higher on several occasions. Fruits of Brons tasted better, and those of Saels II had less taste than those of the standard (Table 34). Fruit size of Saels II lagged a long way behind that of all others, both in 1993 and 1994. In spite of its good productivity, therefore, this two weeks earlier ripening mutant is not of interest for the grower, the more so because of its poorer storability/shelf life and yellower ground colour that may spoil the market for normal Conference. In the period 1991 to 1994, the sugar content of the fruit (in % Brix) of fruit of Saels II was 1 % to 2 % lower than that of the other mutants. Possibly, fruit size, sugar content and taste were negatively affected by the shorter growing season of the fruit and the high yields. Saels II was not virus free. The low production of Conference Massoek and Conference Vlaskamp (not mentioned in Table 34) was probably due to the lower amount of flowering of these mutants. Saels II had more bloom than Saels I and Goud. From the latter two, flowers did not open well in two out of five years. The number of seeds per fruit of these was low in 1994 (Table 34). This and the low productivity may have been caused by this pheno menon. Even fruit size may have been affected, but Saels I clearly is a mutant that produces bigger pears. For Goud this is less apparent. Table 35 gives some data from other taste tests. As in 1994, Verdi was well valued by the taste panel. Dolacomi (Jowil®) tasted roughly the same as Conference. Delbuena from the 1994 harvest obtained a lower score than from the 1993 harvest, possibly because of the high fruit load. The number of fruits per m3 was very high indeed which also led to fruits of a small size. Fruit appearance of Delbuena was also disappointing. Both Dolacomi and Delbuena have low vigour and a compact habit. Fruits of Delmoip (Delbarexquise d'Hiver®, Passadel®) tasted better in February than in November (Table 35). In November fruit texture was still insufficiently melting. Delmoip is a late-ripening French cultivar with apple-shaped fruit that can be stored and kept for a very long time. In 1994, fruits of all pear cultivars were considerably smaller than in former years. This was probably caused by the adverse weather conditions after flowering and the very warm and dry summer months. For example, fruits of Dolacomi were smaller than in the ten preceding years! Therefore, fruits taken for taste tests were also smaller. In 1991, 1992 and 1993 the taste of small Dolacomi fruit especially from heavily-loaden trees, 51 Table 35. Taste scores tests winter 1994/'95 (scale see Table 33) Cultivar November 1994 February 1995 I II Doyenné® du Cornice 7.4 a 7.7 a Verdi 6.6 b Conference 6.6 b 6.7 b 5.6 a Dolacomi (Jowil®) 5.9 c 6.3 b 6.3 a Delbuena (Peradel®) 5.1 d 5.7 c Delmoip (Passadel®) 3.3 d 5.9 a Values in one column followed by the same letter do not differ significantly (P = 0.05). was rated lower than that of larger fruit (> 70 mm). In 1994, the same trend was found but not significantly so (Table 36). Now, fruit < 70 mm received a good rating. Possibly, in a year when fruit size is generally small the critical threshold is lower than in a year when fruit size is more normal. Possibly, the good summer also contributed to the good taste in 1994. Table 36. Taste scores of tests with large and small fruit from trees with heavy and light crops held in November 1994 (scale see Table 33) Crop Size Grading* (mm) Score Grading* (mm) Score Conference Delbuena light large 60-65-70 6.3 a 65-70-75 6.2 ab light small 50-55-60-65 6.3 a 55-60-65 4.9 c heavy large 60-65-70 6.6 a 65-70-75-80 6.5 a heavy small 50-55-60 6.5 a 55-60-65 5.6 be Dolacomi Verdi light large 70-75-80 7.1 a 60-65-70-75 6.8 a light small 60-65-70-75-80 6.6 a 55-60-65-70 6.5 a heavy large 65-70-75-80 6.9 a 60-65-70 6.6 a heavy small 60-65-70 6.5 a 50-55-60 7.0 a Values per cultivar in one column followed by the same letter(s) do not differ signifi cantly (P = 0.05). *) see text. The grading in Table 36 indicated, for example, with 60-65-70 that fruit size of the taste test samples varied between 60 and 70 mm with a peak at 65 mm. From each cultivar large and small fruits from two lightly and from two heavily cropping trees were tested separately. The average production per tree in 1994 for Conference was 22 (light) and 35 kg (heavy), for Delbuena 9 and 15 kg, for Dolacomi 19 and 38 kg, and for Verdi 14 and 31 kg, respectively. Size gradings are given in Table 37. In 1994, as in 1993, the differences in taste between large and small Conference fruits 52 were small and as with Verdi not significant. This is an advantage for this cultivar which bears fruits of a smaller size. Viewing the results from 1991 to 1994, it seems as if the relationship between fruit size and taste is stronger than that between cropping level and taste. The possible relationships between taste, fruit size, and cropping level with Delbuena were studied for the first time in 1994. Large (> 65 mm) fruits were better valued than small ones (Table 36). The effect of cropping was less obvious. The test will be repeated in 1995. For compact growers like Dolacomi and Delbuena vigour on Quince MC does not seem optimal given the low leaf-fruit ratios. Therefore, both cultivars will be tested on the more vigorous Quince MA and BA 29 as well. With non-compact cultivars that also have less flower buds, such as Conference and Verdi, the number of leaves per fruit appears less critical. Conference and Verdi are small-fruited cultivars, Dolacomi has large fruits and Delbuena is intermediate (Table 37). The grade out of Verdi is similar to that of Conference. It even was slightly better (Table 37), but thinning seems necessary to reach a good size. Table 37. Size grading (%) at different cropping levels in 1994 (h = heavy, I = light) Size Conference Delbuena Dolacomi Verdi (mm) h I h I h 1 h I < 60 45.0 11.9 5.7 4.3 2.0 2.9 24.5 18.5 60-65 39.0 39.3 21.4 14.4 12.5 10.9 40.2 30.8 65-70 16.0 41.7 47.9 26.6 36.4 21.5 28.3 40.3 70-80 0.0 7.1 23.8 54.6 49.0 35.7 7.0 10.3 >80 0.0 0.0 1.2 0.0 0.0 29.0 0.0 0.0 Sample size 35 (Conference and Dolacomi), 30 (Verdi), or 18 kg (Delbuena) from two trees. With Dolacomi even in 1994, a year with small fruit sizes, hardly 15 % of the fruits were smaller than 65 mm in diameter. In years with better fruit development and some thinning it is expected that only 10 % will be smaller than 70 mm. Delbuena has short pears and therefore grades favourably, in spite of its fruit weight. Clones of Doyenne du Comice The trial comparing six virus-free clones of Doyenne du Comice (070-WI8612) planted in the spring of 1986 with two-year-old trees on Quince MC rootstock was ended in autumn 1994. Table 38 summarizes some main results. Clones 9-3 and 9-6 produced less than the standard clone M.204. These differences were caused by the smaller tree volume, because there were no differences in productivity per m3. Fruit size in 1994 was good but the average yield level was rather low (on average 10.6 kg/tree). M.204 gave the smallest fruits, both in 1994 and in the preceding years. However, this standard clone yielded, together with clone 10-21, most fruits per tree. Both in 1994 and in former years, fruits of M.204 showed more russeting than those of T 1388 and 53 Table 38. Results of trial clones Doyenné du Cornice Clone 1988 to 1994 1994 Kg/ Mean Grade % Leaf Tree tree m fruit index class index vol. wt. (g) 1" (m3) T1388 70.7 a 47.2 a 317 a 604 b 64.3 a 7.4 a 1.6 a 9-3 42.9 c 35.9 a 294 c 612 b 57.1 a 4.3 d 1.2c 10-21 76.6 a 49.9 a 306 abc 646 ab 59.6 a 6.6 ab 1.6 a 10-28 68.7 ab 46.5 a 313 ab 659 a 52.4 a 6.9 ab 1.5ab M.204 69.2 a 46.7 a 272 d 555 c 45.0 a 6.3 b 1.5ab 9-6 59.0 b 47.0 a 302 bc 618 ab 62.4 a 5.3 c 1.3bc Values in one column followed by the same letter(s) do not differ significantly (P = 0.05). * Sum of weight percentages multiplied with an increasing index per size class; the higher the index the larger the lot. *" graded for russeting; the higher the % the less russeting. *" index scale: 1 = poor (early red discoloration) to 9 = healthy green. 10-21, but the differences were not significant. Fruits of M.204 T 1388 and 10-21 were analysed for minerals, sugar and acids. Differences were very small. The leaves of the various clones differed in appearance. The degree of early red discoloration in August varied greatly. This symptom is reminiscent of pear decline, a mycoplasm disease. Already in 1987 and 1990, 9-3 and 9-6 showed a fair amount of such early leaf discoloration. All other clones did not and were alike. In 1994 also, 9-3 and 9-6 showed most early red discoloration (Table 38). This phenomenon, however, could not be ascribed to mycoplasms, because these could not be detected with the DAPI test in a root sample taken in November 1994 by the NAKB (from T 1388, 9-3, 10-21, M.204, and 9-6). In the 1980's 9-3 and 9-6 showed already symptoms of early red leaf discoloration and also low vigour in the mother tree garden of the NAKB. Two others, 10-21 and 10-28, showed the opposite - healthy leaves and greater vigour. Perhaps, damage of winter frost caused by the severe frost in January 1985 (during the raising of the trees of the trial) may have also had a bearing on the differences in leaf colour. During the nursery period, the same differences in leaf colour and vigour could be observed. With T 1388, 10-21, and M.204 a new trial is being made. These clones have been budded in September 1994 onto Quince MC rootstock both with and without an interstem. These trees will be planted in a commercial orchard. Regional cultivar trials In the spring of 1994, a trial (070-GE/NU/ZE9411) was planted in the experimental gardens in Geldermalsen, Numansdorp and Zeewolde, and in two commercial orchards in Limburg with Verdi on Quince MC rootstock with or without an interstem of Doyenné du Comice. On one of the holdings in Limburg atria l was also planted with Dolacomi on Quince MC and Quince Adams (070-GE/NU/ZE9415). These trials are meaning to evaluate both cultivars on various root- and interstocks. 54 Cultivar testing with stone fruit H. Kemp, H. Wustenberghs, and H. Balmer Cultivar trials with plum in Wilhelminadorp H. Kemp In 1994, nine cultivars were included in the evaluation, amongst these three Rumanian and two German cultivars. Within the framework of mutual collaboration between the Research Station at Wilhelminadorp and the Fruit Centre at Rillaar, belonging to the University of Leuven in Belgium, these cultivars were also planted at Rillaar. Two cultivars were removed from the collection: Madeleine from Sweden (planted 1992; because of moderate taste and gummosis in and outside the fruits) and V72511 from Canada (planted 1992; because of moderate taste and unattractive fruits). The cultivars Avalon, Excalibur, Jubileum, Valor, and Voyageur did well again in 1994 (Table 39). Table 39. Results with some plum cultivars in 1994 Cultivar Plant Kg/ Fruit Fruit Eating Picking year tree wt. shape quality date (g) Opal 1989 12.2 34 elliptic round good early Aug Voyageur 1992 1.3 52 oval-oblong very good 1s t week August Avalon 1991 6.4 63 elliptic round good mid-Aug Reine-Claude Souffriau 1987 7.2 54 round good mid-Aug Jubileum 1988 15.0 80 oval-oblong fairly good mid-Aug somewhat flat Excalibur 1991 8.1 72 elliptic round (fairly) good 3rd week August Victoria 1989 52 oval-oblong fairly good end Aug Valor 1992 0.7 70 oblong oval good 2nd week Sept Anna Späth 1989 25.2 46 elliptic oval good 3rd week Sept All trees in Wilhelminadorp are on St. Julien A rootstock and planted at 4.0 m x 2.75 m. In 1990 and 1991, crop was absent due to spring frost. This should be kept in mind with regard to the figures in Table 39. Avalon and Jubileum give red-blue plums, Valor and Voyageur dark blue and Excalibur orange-red. Anna Späth, Avalon, Excalibur and Voyageur proved fairly susceptible to fruit cracking after rain, probably even more so than Victoria. 55 Cultivar testing cherry in Ahrweiler (Germany) M. Balmer and H. Kemp In 1994, the existing collaboration between Belgium and The Netherlands in the area of testing of stone fruit cultivars was extended to a German institute, namely the 'Staatli che Lehr- und Versuchsanstalt für Landwirtschaft, Weinbau und Gartenbau' in Bad Neuenahr-Ahrweiler (SLVA Ahrweiler). In Germany most plum work concerns prunes, so the information obtained is not very relevant for Belgium and The Netherlands where plums are dominant. However, their work on cherry is of special interest. In 1994, SLVA Ahrweiler had 75 plum/prune, 90 sweet cherry and 20 sour cherry cultivars un der evaluation. In Ahrweiler, some sweet cherry cultivars look promising. These are arranged below according to the ripening week (1st week is the week of ripening of Hâtif Burlat). 3-4th week: Giorgia, firm, 8-9 g, low susceptibility to cracking. 4th week : Cognac, 7-8 g, low susceptibility to cracking. 5th week : Schneider's Späte Knorpelkirsche, 8-9 g, firm, cracking susceptible 5-6th week: Kordia, 8-9 g, firm, long fruit stalk, moderately susceptible to cracking 7th week : Regina, 8-10 g, firm, long fruit stalk, low susceptibility to cracking 7-8th week: Sweetheart, 8-9 g, firm, low susceptibility to cracking, self compatible Within the sour cherries the cultivars Gerema and Karneol are promising. Cultivar testing sweet cherry in Rillaar (Belgium) H. Wustenberghs and H. Kemp At Rillaar, about 100 sweet cherry cultivars were under trial in 1994. Almost all cultivars are on Damil (GM 61/1); a small number are on Camil (GM 79) or Colt. Vista was picked on 30 June, five days before Garnet and Hartland. Productivity and fruit size (7.5 g) of Vista were quite good for an early ripening cultivar; however, firmness and cracking resistance were low again this year. Garnet (8.1 g) and Hartland (7.3 g) yielded (very) well. Hartland was rather firm; Garnet was firm. Summit was harvested on 10 July. Fruit size was very good, but the production of the seven-year- old trees was just moderate. With Sunburst (12 July) the same was true. Maru (Ruby) produced very many but too small (6.9 g) fruits. Ruby (12 July) was rather firm. Somer set (13 July, very firm, 7.5 g) yielded rather well. Sylvia (13 July) produced moderate ly, but had large (9 g) and firm fruits. The Canadian selections 13S-33-34 and 13S-49- 24 were picked on 14 July. Production of 13S-33-34 was very low. 13S-49-24 yielded rather good, but the fruits (8 g) were soft. Lapins (18 July, 8.3 g), Regina (26 July, 10.9 g) and Sweetheart (29 July, 8.6 g) were all firm and moderately productive. 56 The pollination of pome and stone fruit H. Kemp Crossings Annually, crossings are made between cultivars of apple, pear and plum in order to see which combinations can be planted together safely in practical situations. In 1994, crossings with all three crops were carried out in Wilhelminadorp and also for apple in Numansdorp and pear in Geldermalsen. However, the plum crossings in Wilhelminadorp and in Horst failed. Per crossing 100 (sometimes 50) flowers were used. After pollinati on the stigmas were covered with vaseline. Results of the apple and pear work are summarized in Table 40. Table 40. Percentage fruit set and number of good seeds/fruit at harvest in 1994 Pollinated Pollinizer Fruit Seeds/ cultivar set fruit Apple Co-op 29 CPRO 78038-9 60 3.0 Enterprise 64 5.7 Cox's Orange Pippin X4876 65 5.0 CPRO 78038-9 Co-op 29 33 7.1 CPRO 78038-9 (selfed) 13 3.8 CPRO 78039-18 Discovery 29 1.2 Vanda 24 1.3 Elstar X4876 40 3.8 Enterprise CPRO 78038-9 8 5.0 Jonagold Discovery 9 1.3 Vanda 34 4.5 Vanda Co-op 29 19 4.2 CPRO 78038-9 19 4.3 Discovery 21 3.5 Pear Conference Goud Conference Goud 33 0.0 Verdi 29 0.6 Delbuena Conference 29 1.2 Doyenné du Comice 23 1.2 Verdi 28 1.1 Gieser Wildeman Concorde 8 1.0 Conference 2 2.0 57 Most combinations of scab-resistant cultivars (CPRO 78038-9 and 18, Co-op 29, Enterprise, Vanda and Discovery) gave excellent set. The combination CPRO 78039-18 x Discovery was also good in 1992 and the combination CPRO 78039-9 x Co-op 29 gave fairly good set in 1993. The flowering periods of all these cultivars have just sufficient overlap for mutual benefit. An exception was the combination Enterprise (= Co-o p 30) and CPRO 78038-9. In 1993 also this combination had a very low set. Probably, these cultivars have the same S-alleles. The fruit set and seed number of CPRO 78039-9 after selfin g were very high. Therefore, this cultivar is probably (partly) self-compatible. This selfing will be repeated in 1995. Jonagold flowers pollinated by Vanda pollen set well, but Discovery pollen was clearly less effective. In earlier work Discovery did better. The flowering periods of Jonagold, Discovery, and Vanda match well. The red leaved ornamental Malus X4876 (with a dominant gene for red colour) gave high fruit and seed set with Cox's Orange Pippin and Elstar. This Malus has been planted in an orchard with these two apple cultivars to establish the range of a pollini- zer. So, pollen compatibility will not be a limiting factor in this study. With pear, selfing Conference Goud, a large-fruited Conference mutant, gave fruit and seed set comparable with selfing of standard diploid Conference. In 1983, 22 % fruit set was obtained with 0.0 full seeds per fruit after selfing. The results of the crossing Conference Goud x Verdi agree with those obtained earlier in Belgium with standard Conference. So, Conference Goud is probably diploid as well. Both Conference and Doyenné du Comice gave good fruit set on Delbuena, which corresponds with French data. Verdi pollen gave good fruit set, too. The overlap in flowering time of these cultivars is sufficient to ensure mutually good pollination. The combinations Gieser Wildeman x Concorde or x Conference, made in Geldermalsen, gave poor set, but earlier crossings gave good set. Flowering times match well. 58 SmallFruit Strawberry cultivar trials J. Dijkstra and A.A. van Oosten Glasshouse strawberries At the experimental centre in Breda, 10 CPRO selections and the French cv. Darline were compared with Elsanta, Primella and Karola. None of the selections was an improvement compared to the standard cultivars. Darline gave very nice large fruits and with few of second quality, but production was too low. Cultivars in the open Nationaltrial with June-bearing cultivars The national cultivar trial was carried out at the Research Station as well as at the experimental centres in Breda, Geldermalsen, and Horst. Eight CPRO selections and five cultivars from abroad were compared with Elsanta and Lambada. Yields were satisfactory. However, the spread of the harvest period was very limited. Most selections and cultivars ripened at the same time as Elsanta. Only Lambada, Cortina and Gardena were three to six days earlier and CPRO 9404 ripened five to six days later than Elsanta. A number of cultivars and selections was rejected for different reasons. Productivity of CPRO 9301 was too low, CPRO 9401 had insufficient flavour, fruit size of 9404 was too heterogeneous and its fruits were only moderately firm. Furthermore, fruits of CPRO 9406 had insufficient flavour and firmness. With regard to the Italian cultivars, productivity of Cortina was too low and the plants showed June yellows. Fruits of Gardena were very heterogeneous and too dark red and taste was poor. Sella also had irregular fruits. On sandy soils productivity of Sella was moderate, but on clay soils productivity was good. The Swiss cultivar Gerida gave a reasonable to good production. However, fruit colour stayed white around the calyx and taste was rather flat. The French cultivar Darline attracted attention by its bright orange-red fruits and the very regular fruit shape. Both, firmness and taste were good. Unfortunately, yield was insufficient at all four sites. By planting this cultivar more densely, productivity per ha can probably be raised. The following CPRO selections were held over for further judgement in 1994: 9302, a short, compact plant type with a reasonable to good production. Fruits had sufficient firmness, were red to dark red, juicy with a pleasant somewhat fresh sharp taste. Seems only slightly susceptible to Verticillium. 9402, a short compact plant with a good yield. The somewhat oblong fruits had an orange red to red colour, were sufficiently firm and juicy and had afres h taste. 9405., grew only moderately, and had a reasonable to good productivity. Fruits were red to dark red, sufficiently firm, juicy and had a good taste. 9407, a strong growing, but open plant type with long fruit stalks. Productivity was good to very good. However, fruit size was only moderate. Fruit colour was bright red 59 to red and fruits were firm and only slightly vulnerable with a nice fresh sharp taste. European cultivar trial The European strawberry cultivar working group started a trial in which cultivars from breeding programs in Southern and Northern Europe are compared under very different circumstances. The aim is to find out how far new cultivars are adaptable to different climatological conditions. For breeders this is important in connection with the choice of parents for their breeding programs; for growers this is important in connection with a rapid introduction of new cultivars. In the Netherlands, the first trial was planted in a glasshouse in Breda and in the open in Horst. Mainly new cultivars from south-European breeding programs were included. Productions were low, due to the fact that only small plants were available. However, a first impression of fruit quality was obtained. Most cultivars had a disappointing taste. None of the new cultivars was an improvement compared to Elsanta. Further arrangements were made for a uniform scheme of observations and statistics. Trialwith cold-storedwaiting-bed plants In Breda and Horst, five CPRO selections were compared with Elsanta. In Breda the planting date was 19 May, in Horst 1 June. Production of most selections and of Darline was lower than that of Elsanta. Only, CPRO 9407 was a positive exception. Selections 9402, 9405 and 9407 will be judged again in 1994. National trialwith everbearing cultivars At the experimental centres in Breda and Zwaagdijk as well as at the Research Station, again some new everbearing cultivars were compared with Rapella. Most trials were carried out in the open, but in Wilhelminadorp all cultivars were also planted in peat bags under a plastic cover. Table 41. Results of the trials with everbearing cultivars Cultivar Kg/m2 1st quality Average fruit weight (g) 1st qu. Breda Z.dijk W.dorp W.dorp Breda Z.dijk W.dorpW.dorp *) ") *) *') Rapella 2.02 3.08 2.56 3.85 17 19 13 12 CPRO 1036 1.44 1.59 1.68 3.85 17 17 14 13 Evita 2.41 3.35 2.76 5.39 16 19 16 13 Calypso 2.19 2.86 2.15 5.39 18 17 13 12 Mrak 1.16 2.46 1.54 2.47 15 25 19 17 *) in the open **) in peat bags u nder plastic At all sites, plants were planted at the end of February, forced for four to six weeks under glass or plastic and planted on the production fields in April. 60 The harvest period started in July and ended in Breda at the end of September and in the open in Zwaagdijk and Wilhelminadorp mid-October. Under plastic, fruits were picked until mid-November. From the results summarized in Table 41 it is clear that Evita gave the highest producti on in all trials. Production of CPRO 1036 was disappointing in the open but very good in peat bags. Production of Calypso was reasonable to good and that of Mrak was mostly only moderate. The main characteristics of the cultivars under trial are: Rapella: good growth and productivity. Fruits pale to bright red, often somewhat irregular, only moderately firm and with a reasonable to good taste. Very susceptible to mildew. CPRO 1036: growth in the open only moderate, in peat bags good. Productivity in the open only (very) moderate, in peat good. Fruits reasonably large, short, conical and with a bright orange-red colour. At the end of the harvest season the colour around the calyx stayed white. At first, firmness sufficient, at the end of the harvest season fruits were sometimes very soft. Taste very good. Only moderately susceptible to mildew. Evita: growth somewhat disorderly with pale green leaves. Plant height in the open somewhat irregular, but productivity very high. Seems susceptible to stress, but has a good recovery. Fruits until the end of the harvest period nice conical and evenly bright red coloured. Firmness better than that of Rapella but less than Elsanta. Taste reasona bly good. Only very little susceptible to mildew. Calypso: growth strong with a reasonably good production. Fruit size reasonable to good, but fruit shape often irregular. Taste only moderate. Moderately susceptible to mildew. Mrak: growth moderate to good. Production only moderate. Fruits dark red, big and very firm. Taste good. Susceptible to mildew. At the Research Station also Sunset was also evaluated. Fruits of this cultivar were large with a nice red colour and good firmness. However, due to the very high suscepti- bilty to mildew production could not be estimated. Cultivar trials of bush and cane fruits A.A. van Oosten Red currant Firstscreening of new cultivars in the field In 1985, a first screening trial was established with 21 cultivars or selections of red and white currants, including some standards. During the course of the trial a number of new cultivars or selections were grubbed because of poor performance. These were: A32, A105, B11, Jotun, London Market, Mactor, Nortun, Redstart, and Soeur de Claire. Others were found promising, namely: Augustus, Cassa, Detvan, Junifer, Roodneus, Rosa Sport, and Tatran. The cultivars 1967 and Herosta are still being evaluated. In the Annual Reports of the Research Station from 1985 to 1993 descriptions of all these 61 cultivars have been given . In 1993 and 1994, another 15 cultivars and selections were planted. Amongst these were: Cocagne, EM1503/35 = Redwing, Fertöd, Hron, Jodes, Mivana, Mulka, Präkan- da, Redpoll, and Traubenwunder. It is still too early for any conclusions. Also in 1993, a cultivar trial was planted on two sites (Geldermalsen and Wilhelminadorp) with 16 cultivars bearing red, pink, or white berries. First fruits were obtained in 1994, but it is too early for any conclusions. In 1994, a number of crossings were planted that came from a private breeding programme aimed at early ripening, high berry quality, and disease resistance. Also in 1994, a trial was planted at a private holding in Heinkenszand to evaluate six cultivars (Prince Albert, Rode Rebel, Rondom, Rotet, Rovada, Stanza) for mechanical harvesting. All six cultivars have a suitable habit for machine harvesting. Firstscreening of new cultivars in aplastic tunnel In 1993, the following red-currant cultivars were planted in a tunnel in 10-l-pots: Fay's Prolific, Fortun, Herosta, Jonkheer van Tets, Junifer, Laxton no.1, Laxton's Perfection, Nortun, and Red Lake. Three white currants (Albatros, Werdavia, and Zitavia) and one pink-currant (Rosa Sport) were included. All cultivars are early-ripening. After the harvest of 1994, the Norwegian cultivars Fortun and Nortun were grubbed, because the flower-bud formation was very poor (probably because of lack of winter chilling) and therefore production was too low. Fortun produced only 0.12 and Nortun 0.19 kg/m2 as against 1.40 for Junifer. Apparently, these cultivars are not suited to culture under cover. Origins of Rode Rebel From the cultivar Rode Rebel six origins are being compared in order to establish trueness to type. Selection 1967 looks very much like Rode Rebel, but Geldermalsen 1 and 3 vary from all other origins in growth habit and berry type. Selections ofRondom As Rondom shows variations in habit in the field, it was decided in 1985 to start a comparison of four clones of Rondom. The trial was set up with six replicates with five Table 42. Flowering and cropping data from 1994 of Rondom-selections Rondom Date Date Kg/100 100 Truss Berries/ selection begin harvest m berry weight truss bloom weight(g) (g) J 25-4 18-8 114 78 8.6 10.9 H 18-4 1-8 444 81 12.0 14.8 G5 18-4 25-7 399 70 10.9 15.5 R-a 18-4 3-8 361 71 9.8 13.6 R-b 25-4 18-8 223 82 11.3 13.6 62 plants per plot. After the harvest of 1994 the trial was ended. Main results of 1994 are given in Table 42. No deviating plants were observed, except for one plant in Rondom J. In practice, too, plants with deviating behaviour have been found in Rondom J. So, this selection is not a stable one. In 1988, Rondom J came into leaf later than the other selections and also flowering and harvest were retarded. Although berries from Rondom J were larger, production equalled that of other selections. From 1988 onward. Rondom J bushes came into leaf with great difficulty. Some buds did not develop at all. As a result, production and berry quality of Rondom J were negatively affected. It was assumed that this abnormality was due to lack of winter chilling. Given this phenome non. Rondom J can not be recommended any more. The same applies to Rondom R, because in the trial the same problem was observed in two replicates. Up to 1993, Rondom G5 and H gave good results, but in 1994, G5 showed poor leaves, inadequate Table 43. Effect of start date and duration of a cold treatment on the leafing of Rondom J. Numbers of Numbers of leafed buds/bush weeks of Starting date chilling period chilling 8 February 8 March 5 April 3 May 0* 4 9 12 18 21 8 22 19 30 12 31 34 16 40 - - - * 11 buds had leafed when there was no chilling at all Table 44. Effect of cold treatment and application of rest-breaking agents on the leafing of Rondom J. Treatment/Date Cold treatment from 8 February until 5 April yes no Untreated 22 11 Rest-breaker 1 -6 % Vbc 8 February - 12 -6 % Vbc 12 April 28 14 Rest-breaker 2 -conc.1 12 April 17 13 -conc.2 12 April 17 8 -conc.3 12 April 17 13 Rest-breaker 3 -conc.1 12 April 14 11 -conc.2 12 April 19 8 -conc.3 12 April 16 11 Rest-breaker 4 -3 % mineral oil 12 April 17 22 63 growth, and smaller berries and lower production than Rondom H. Therefore, G5 must be discarded as well. To summarize, Rondom H appeared the best selection. It starts growing a little earlier than the other selections and flowering is also somewhat advanced (except in 1994). Possibly, Rondom H has lower chilling requirements than the other selections. Chilling requirements Rondom J In 1994, research on the chilling requirements of Rondom J was ended. In that year, again a study was made on the bud rest as in the previous season (see Annual Report 1993, p.74). The various treatments are mentioned in Tables 43 and 44. Table 43 shows that a short period of four weeks of chilling only exerts an effect when applied late. Cold periods that started earlier needed to be applied for at least eight weeks. The longer the cold period the more effect on the bud number that leafed. The results show that cold requirements play a rôle in the leafing of buds of Rondom J. From Table 44 it can be derived that only mineral oil had an effect without a cold treatment. With chilling, only Vbc had a small effect. None of the chemicals used had a value of any practical significance. Black currants Firstscreening of newcultivars In 1991, a comparison of black currant cultivars and selections was started. After the 1994 harvest, four cultivars were removed from the collection because of poor behaviour. These were Eva, Troll, Tifon, and Viola. In 1994, Eva was the most productive cultivar in the trial, but in the two preceding years productivity was only moderate. Moreover, Eva proved very susceptible to mildew. The upright habit and vigorous growth make Eva suitable for machine harvest, but the negative features were decisive. Troll and Tifon were discarded in spite of their high productivity, because their drooping growth habit makes them unsuitable for machine harvest. Moreover they proved very susceptible to mildew. Viola was discarded because of moderate productivity and mildew sensitivity. The following cultivars were all more or less susceptible to mildew: Ben Lomond, Ben Nevis, Black Down, Black Reward, Eva, Ometa, Phoenix, Silgo, Spoernik, Tifon, Trench, Troll, Tsema, and Viola but the cultivars mentioned hereafter did not show any symptoms of mildew although no fungicides were applied: Andega, Ben Alder, Ben Connan, Ben Loyal, Ben Tirran, Ben Tron, Ceres, ECM, Haakon, Kristin, Ojebyn, Titania, and Triton. In 1994, another eleven cultivars were included in the trial. In 1994, eight cultivars were planted at a grower's site in Ovezande to evaluate their suitability for mechanical harvesting. Cultivars included are: Andega, Ben Alder, Ben Lomond, Ben Nevis, Ben Tirran, Phoenix, Titania, and Triton. 64 Gooseberry Firstscreening of newcultivars In the years 1989 to 1991, 14 cultivars were planted for evaluation, with Whinham's Industry as a standard. The trial was ended after the 1994 harvest. Main results are given in Table 45, where the cultivars are arranged according to the date of the begin ning of harvest. Weisse Neckartal is a vigorous grower with pale green, round, lightly haired berries with good taste. The cultivar is susceptible to mildew. Invicta is a vigorous grower with some thorns, and is very productive. The fruits are somewhat irregularly shaped, pale green and hairy with a flat taste. Table 45. Results gooseberry-cultivar trial Cultivar Kg/100 Mean fruit Date Date m2 1st weight begin begin quality (9) bloom harvest Averaged for 1991 to 1994 Weisse Neckertal 59 10.1 3 April 27 June Invicta 238 10.1 10 April 28 June Early Sulphur 73 6.1 10 April 29 June Greenfinch 44 7.8 12 April 30 June May Duke 77 10.0 2 April 4 July Goudbal 78 9.6 12 April 8 July Starfructa Dunkelrot 135 10.8 6 April 9 July Whinham's Industry 161 12.2 9 April 10 July Rosko 96 9.2 15 April 10 July Golda 97 10.2 11 April 10 July Achilles 90 12.3 3 April 14 July Averaged for 1992 to 1994 Pax (EM 1815/123) 86 11.3 10 April 30 June EM 1815/125 64 11.0 12 April 5 July EM 1815/133 70 14.5 10 April 8 July EM 1503/31 36 9.3 17 April 8 July Greenfinch grows with moderate vigour and has a spreading habit. The fruits are smooth and green and have afla t taste. Mildew was not observed. May Duke grows upright and vigorously and has a moderate number of thorns. The berries are bright red, round and almost completely smooth and taste well. The cultivar is moderately susceptible to mildew. Goudbal grows with moderate vigour and bears oblong, golden-yellow berries that taste well and show little susceptibility to rain. Goudbal is moderately susceptible to mildew. Starfructa Dunkelrot is a moderate grower with dark red, slightly hairy fruit that taste 65 well. The cultivar is moderately susceptible to mildew. Rosko grows with moderate vigour with strong spreading branches. The fruits are bright red, smooth and taste well. Rosko appears not susceptible to mildew. Golda grows fairly strongly and bears round, smooth, yellow berries that taste well. It is fairly susceptible to mildew. Pax grows moderately strongly and possesses only a few thorns. The berries taste well. Mildew was not observed. EM 1815/125 grows with moderate vigour and has only a few thorns. Mildew was not observed. The berries are round, hairy, and bright red and of moderate taste. EM 1815/133 grows rather vigorously and has only a few thorns. Mildew was not observed. The berries are fairly round, hairy and bright red. EM 1503/31 resembles EM 1815/133 and here, too, mildew was not seen. Two cultivars planted in 1993, could not yet be properly judged, but the observations so far are: Mucurines has a strong growth and is very thorny. The fruit is smooth, green and of moderate taste. Mildew was not observed. Black Velvet is also a vigorous grower with many thorns that bears very small fruits of dark red to almost black colour. Here, too, no mildew was seen. In the winter of 1994/'95 a new trial was planted with 15 cultivars, but due to loss of staff, its future has become uncertain. Raspberry Firstscreening of newcultivars In spring 1993, four cultivars were planted under plastic covers to protect them from the rain. So far, the following results have been obtained. Granat suffered from root and cane diseases and therefore production was rather low. The fruits were of moderate quality: small, dark and of moderate taste. Redsetter grew well and production was good. Fruits were cone-shaped, dark, rather soft and of moderate taste. Himbo Queen also suffered from root and cane diseases. Fruits looked very attractive: large, not too dark, sufficiently firm and of good taste. Glen Lyon grew well and gave round, firm but rather acid fruit. In spring 1994, ten cultivars were planted: 71/11/153, Algonquin, Beskid, Elida, Gaia, Julia, Pechts Giant, Proma, Resa, and Tulameen. The plants developed well. Cultivartrial in plastic tunnel In 1994, ten cultivars were evaluated in a (10 I) pot culture in a plastic tunnel. Main results of 1994 are given in Table 46, where the cultivars are arranged according to the date of the beginning of harvest. Glen Moy was the earliest in ripening. Production was low due to root diseases. Glen Clova was very productive, but fruits remained too small. Glen Lyon was a healthy grower and fruits were bright red, round and firm, but their taste was rather acid. The berries were hanging under the leaves and could be easily 66 picked without their plug. Glen Prosen ripened early in comparison with former trials. The fruits were also larger than usual. Elida made slender canes with fairly long fruiting laterals. The fruits were clearly visible, lightly coloured and of good taste, and could be picked easily without plugs. Table 46. Results 1994 raspberry trial 088-WI94610 Cultivar Kg/100 % 1st Mean Harvest date m2 *) quality fruit 5% 50% 95% weight (g) Glen Moy 137 84 4.0 27 May 9 June 26 June Glen Clova 222 90 3.5 30 May 13 June 1 July Glen Lyon 186 86 4.2 1 June 13 June 28 June Glen Prosen 174 93 4.6 5 June 16 June 30 June Elida 179 86 4.3 5 June 20 June 6 July Ru 74 71 45 4.0 8 June 15 June 24 June Gradina 202 86 4.0 8 June 18 June 28 June Eversdijk 100 86 3.9 8 June 18 June 25 June Himbo Queen 208 84 5.0 9 June 23 June 8 July Tulameen 101 92 5.7 11 June 21 June 6 July ") 1st and 2nd quality. Ru 74 did not emerge well as a result of cane dying, which hampered production. This cultivar has been discarded. Gradina proved a valuable cultivar with well-shaped, pointed, bright red fruit that tasted well. Eversdijk was disappointing due to cane diseases. Himbo Queen had very long fruiting laterals that broke easily. Fruits were nice, large, light red, fairly soft and of good taste. Tulameen, too, had long fruiting laterals. Fruits were very large, firm with a good colour and taste. Production was only moderate because canes were too short. Cultivartrial under rain cover In spring 1993, a trial was planted with ten cultivars on two sites (Geldermalsen and Wilhelminadorp) under rain covers. After the harvest of 1994 the following, four cultivars were removed because of Phythophthora-root diseases: Comox, Glen Clova, Glen Moy, and Gradina. The trial is being continued with the remaining cultivars. Cultivartrial with cold-storedplants In non-heated plastic tunnel a trial with ten cultivars for a delayed culture was evalua ted. The following conclusions were drawn. Elida did not produce well because not all buds developed, but fruits looked attractive. 67 Eversdijk was fairly productive with firm, well-coloured fruits that tasted well. Glen Clova was productive but the fruits remained too small. Glen Moy was not productive enough as a result of canes being too short, and because many buds did not develop. Fruits, however, were large. Glen Prosen was also fairly productive and yielded very firm, but rather small fruits. Gradina was fairly productive and gave well-coloured but rather soft fruits. Himbo Queen was productive and produced large, well-coloured and tasty fruits. Marwé came up with expectations because production was very good and fruits were large and well-coloured. This cultivar is well suited for a late culture with cold-stored plants. Tulameen was only moderately productive because the canes remained too short. Fruits were large, firm and of good colour. Cultivartrial with primocane fruiting cultivars Various cultivars are being evaluated in a cold tunnel and result can be summarized as follows. Dinkum is a hybrid of Autumn Bliss and Glen Moy that can not be recommended, because although production equalled that of Autumn Bliss, fruits were smaller and less beautiful. The leaves showed atypicall y early autumn discoloration. Douglas (BRu 8802-1) grew moderately well and the fruits somewhat resembled those of Autumn Bliss, but could not be easily picked without a plug. Favourite was a vigorous and healthy grower with strongly-thorned canes. Production was good, but the pointed fruits, although large, were of moderate quality: fairly dark, irregular and of moderate taste. Galante grew vigorously and healthily and yielded well. The late ripening fruits were very large, regular, well-coloured, but vulnerable and of moderate taste. Luilin resembled Ruby but the canes were less thorny. Fruits were large, bright red and crumbly. Polana produced better than in preceding years and ripened earlier. Fruits were of good quality, but smaller than those of Autumn Bliss. Rossana grew moderately but production was still low. Fruits tasted very well. Ruby is a hybrid of Heritage and Titan and grew well. Canes were very thorny. Production was good. Fruits were large, crumbly, of moderate taste and could be picked easily without a plug. Ripening was earlier than last year. Blackberry Firstscreening of newcultivars In the springs of 1993 up to 1995, 20 cultivars have been planted for evaluation. Some observations on some cultivars can already be recorded. Arapaho is thornless. In 1994, shoot tips died for unknown reasons (no fungus could be detected). High temperatures might have been involved. Bodermó is thorny and resembles a hybrid of Silvan and Kotata. Chester Thornless proved to be another cultivar, probably Navaho. The plants were thornless and produced only moderately. Jam Fall Black resembled Thornfree in fruit characteristics. Jumbo was productive and yielded very large, firm and acid fruits. 68 Kotata ripened four days later than Silvan, but production was lower and fruits were smaller. Both are thorned cultivars. Waldo was the earliest ripening cultivar in 1994. The production was only moderate and the plants developed slowly. Screening bushand canefruits for disease andpest susceptibility With the aim of establishing the sensitivity to the main diseases and pests, a special block was planted with a large number of cultivars of the various bush and cane fruits. This effort is important because only a small and decreasing number of pesticides is available for these crops. Moreover, the government policy is aimed at reduction in pesticide use. In total 43 red currant, 47 black currant, 58 raspberry, 19 blackberry, and 20 gooseberry cultivars have been planted. Development of methods for an early and late harvest of currants, raspberries, blackberries and blueberries J. Dijkstra and A. Scholten Raspberry Planting datesfor an earlycrop in containers (Geldermalsen) As a continuation of the 1993 trial, a new trial with planting dates was carried out in 1993/'94. Plants, lifted in November 1994, were stored partly outdoors in sand ("wet" storage), and partly in a shed wrapped up in plastic ("dry" storage). These plants were planted in containers in December, January, February or March for comparison with plants planted directly after lifting in November and December. The cultivar was Glen Moy. Due to inexplicable circumstances quite a number of canes did not develop well and died. The percentage of plants that failed to grow was about equal for dry and wet storage. Although the circumstances call for care to be taken with conclusions, the impression is that dry storage resulted in higher yields than wet storage (after correcti on for dead plants). This result is surprizing because it was expected that dry storage would give poor results. Of the different planting dates, December gave the best results (for stored plants as well as for direct planting). An earlyand late harvest withprimocane fruiting raspberries (Geldermalsen) An investigation was made to ascertain whether it is economic to harvest primocane fruiting raspberry canes in spring after the upper part of these canes has given a production in autumn. The production was compared with that of newly planted primo- cane fruiting plants and of summer fruiting raspberries (an early crop of newly-planted canes, followed by a late crop with cold stored plants). The results are summarized in Table 47. Naturally, the plants of Autumn Bliss that were planted in Spring 1994 produced no yield before the 1 July. However, yield of the spring crop of the older 69 Autumn Bliss plants was good, with a high percentage first quality and large fruits. In the second half of the year the production of the young canes of the older plants was clearly less than that of the young canes of the spring planted Autumn Bliss. Of the summer fruiting raspberry cultivars Glen Moy was very unsatisfactory, due to problems with the plants. In spring Marwé gave a satisfactory production but due to high temperatures in summer the production of the cold stored plants was very disappointing. Table 47. Results of an autumn and spring crop with primocane fruiting raspber ries Cultivar/Treatment Harvest spring 1994 *) Harvest autumn 1994 *) kg 1/ % 1st average kg 1/ % 1st average m2 quality fruit m2 quality fruit weight(g) weight(g) Autumn Bl. spring 1994" 1.20 83 5.1 Autumn Bl. spring 1993" 1.58 87 5.4 0.84 65 4.8 Autumn Bl. spring 1992" 1.56 86 5.5 0.66 79 4.9 Glen Moy"" 0.13 53 3.6 0.13 44 3.9 Marwe"" 1.20 82 5.0 0.41 78 4.2 Glen Prosen"* 0.82 83 4.8 0.43 78 4.2 spring = until 1 July, autumn = from 1 July planted in spring 1994, spring 1993 and spring 1992 resp. *" spring planting in 1994, followed by a planting at the beginning of June with cold- stored plants Red currant Multi-year culturein containers (Geldermalsen) After three harvest years, in the winter of 1993/'94 the plants in containers were partly replanted in the soil. From a number of containers the bottom was removed so that the plant roots could grow into the soil. With cv. Jonkheer van Tets there was almost no difference between the treatments, with cv. Junifer the plants that stayed in the containers produced about 17 % more than those that were replanted. Furthermore, Junifer was far more productive than Jonkheer van Tets (2.79 and 1.66 kg/m2, respectively). Moreover, Junifer had more first quality berries and more berries per truss. Berry size was equal for both cultivars. Certainly, the good results with Junifer were partly caused by strong pruning, resulting in many trusses on one-year-old wood. 70 Disease-free propagation of strawberries and other small fruits J. Dijkstra, Sj. Rinsma and W.A.G.M. Jansen Influence of light intensity during the growth of runner plants When growing strawberry plants from unrooted cuttings, the growing method - horizontal or vertically hanging - is still a point of discussion. Growing the runners horizontally makes it easier to plant the cuttings but it increases the risk of infection with soil-born diseases. However, in a system where the runners grow down vertically, light intensity at the bottom can be very low. To answer the question whether this decrease in light intensity influences plant quality, light intensity was decreased by 30 %, 60 % and 75 % in a horizontal system, using different kinds of cloth in the period June - July. No differences in yield were found between the treatments. This suggests that in the middle of the summer a decrease of light does not influence runner-plant quality, at least not in the chosen range. Unrooted cuttings: growing indoors or in the open In 1993 at the experimental centre in Breda, cuttings were taken weekly in the open in the period 19 July to 13 August and in a glasshouse in the period 29 July to 9 September. All plants were grown as tray plants, cold-stored in December and planted in peat bags at the end of July 1994. By counting the number of flower trusses it was clear that they decreased with later dates for taking cuttings. With a similar planting date most flower trusses were formed when the plants were grown in a glasshouse. The conclusion is that, in order to get good plants, cuttings should be taken in the open in the middle of July and in a glasshouse about two weeks later. Plant density and choice of substrate In Horst during the summer of 1993, cuttings of different size were taken and planted in trays with peat and rockwool. In both substrates two plant densities were used. In peat plant densities were 33.3 and 66.6 plants/m2 and in rockwool, 43.8 and 87.5 plants/m2. All plants were grown in an ebb and flow system. The results are summari zed in Table 48. In December, at the end of the growing period, rhizome diameter was largest with the biggest cuttings. However, in the end this turned out not to have any influence on the fruit production. This was in line with earlier trials. Also, the wider plant distance led to stronger plants and it was striking that these plants had clearly more flower trusses, resulting in a higher production (with a somew hat lower percentage first quality). The fact that the results on rockwool were somewhat poorer than those in peat is probably caused by the smaller substrate volume as well as by the higher plant density on rockwool. Furthermore, plants on rockwool turned out to require different amounts of water and nutrients. However, for the present the impression is that cuttings can grow well on either substrate. Plant density seems to have a big influence on plant production. 71 Table 48. Effect planting distance and subtrate during the production of tray- plants Treatment Rhizome- Number of Number of Kg/m2 % 1st diameter flower flowers 1st + 2nd qual. (mm) trusses per plant quality December per plant Peat, 66.6 pl/m2 13.0 1.4 16.3 2.50 94 Peat, 33.3 pl/m2 14.1 2.4 25.6 3.47 91 Rockw. 87.5 pl/m2 12.7 1.5 13.5 1.93 91 Rockw. 43.8 pl/m2 14.0 2.6 21.4 2.93 90 Illumination of tray plants In autumn 1992, it was evident that in tray plants flower development can easily be too rapid, resulting in very poor flower quality of the first trusses in spring. Therefore, in the autumn of 1993 in trials with cuttings it was investigated in Breda and Wilhelminadorp whether this early flowering could be prevented by illumination at the beginning of the flower initiation period in autumn. From mid-August onwards, a long-day treatment was given during one to six weeks. The results show that delay of flower initiation results in a lower production. Even in the untreated plots no unduly early flowering was observed. The conclusion is that it is not meaningful to delay flower initiation but an attempt should be made to take measures to make the plants go dormant as soon as sufficient flower trusses are made. Influence of a gibberellin treatment on flower initiation In addition to illumination, it was also tried to influence flower initiation by spraying 50 and 100 ppm GA3, two to four weeks after planting the cuttings. However, these treatments had no clear effect on flower initiation or production. Lifting dates of tray plants for cold storage Tray plants are often used as cold-stored plants for an autumn crop, or for an autumn crop followed by a spring crop. This means that they have to sustain easily long cold storage. From trials with waiting-bed plants it is clear that the moment of cooling down plays an important role in plant quality after storage. Therefore, in Breda a number of lifting dates of tray plants in the period mid-November to January were compared. The production in autumn of outdoor-grown tray plants varied from 2.25 to 2.50 kg/m2. The highest yield was obtained with plants that were lifted at the end of November when temperatures were around freezing-point. For plants grown in a glasshouse the optimal lifting date was somewhat later. When plants were lifted during the relatively warm month of December production was somewhat lower. The conclusion is that tray plants can be lifted quite early. Probably, this is connected with the fact that the trays take up the temperature of the surrounding air quicker than closed soil. Therefore, the optimal lifting date seems to depend more on the temperatu- 72 re in the preceding period than on the calendar date. Use of tissue-culture plants of Elsanta In principle, the use of tissue-culture plants offers the opportunity to start with healthy plants. Therefore, in co-operation with the Laboratory for Tissue Culture in Roelofa- rendsveen, it was investigated to see if tissue-culture plants can be used directly for fruit production. Plants taken out of tissue culture on four different dates were compa red. Also, for one starting date three hormone levels were compared. The cultivar used was Elsanta. The plants were grown in trays during the summer of 1993 and grown for fruit production partly in spring 1994, partly in autumn 1994. During the growing period in trays many runners had to be removed. The earliest planting date (week 26) gave the highest yield, but the percentage of first quality fruits was somewhat lower (Table 49). In particular, the latest planting date (week 29) gave a low yield. However, there was no clear difference in production between the three hormone concentrations. Table 49. Planting date of tissue-culture plants of Elsanta Planting Plant % multiple Production 1st+ 2n d Average fruit date diameter crown quality(kg/m2) weight (g) (mm) plants in spring in autumn in spring in autumn December Week 26 11.1 24 4.16 1.89 16.1 14.3 Week 27 10.9 20 2.80 1.59 15.4 14.5 Week 28 8.9 1 2.90 1.31 15.4 13.3 Week 29 8.4 5 1.70 1.24 14.1 13.7 Unfortunately, a direct comparison with normally propagated plants was not possible. However, the impression is that the tissue-culture plant production was, at least equal to that of normally propagated plants in other trials in the same glasshouse. Probably, the average fruit weight was slightly lower. Optimizing closed growing systems in strawberry culture J. Dijkstra and Sj. Rinsma Illumination and cold-units At the experimental centre in Breda, research into the influence of low temperatures and illumination on yield and fruit quality of the spring crop was continued in a strawberry culture with cold stored waiting-bed plants in which an autumn crop is followed by a spring crop of the same plants. At the same time three starting dates of heating were compared. The cultivar used was Elsanta. For the definition of the amount of cold that was given a method developed by the Advisory Service (D.L.V.) was used. In this calculation method it is assumed that 73 temperatures between 0 ° C and 8 °C contribute to the amount of cold which strawber ry plants need. Each degree below 8 °C per day means one cold unit (one day 6 °C is two cold units; one day 3 °C is five cold units). By overwintering the plants in different glasshouses 0, 40, 66 and 96 cold units were realized. From the results in Table 50 it appears that the starting date of heating had only little effect on production but a somewhat greater effect on fruit size and mean harvest date. Without illumination 66 to 96 cold units were necessary to obtain maximum yield. With illumination less cold units were satisfactory (40-66). Fruit size and percentage first quality increased when more cold units were given. Illumination had a positive effect on Table 50. Effect of illumination, cold units and starting date of heating on produc- tion and fruit quality of Elsanta. Treatment + illumination - illumination forcing Cu's* kg/m2 % average mean kg/m2 % average mean date 1st fruit harvest 1st fruit harvest qual. weight date qual. weighlt date (g) (g) 1 Feb 0 5.7 66 15.4 6 May 4.9 55 15.4 8 May 1 Feb 40 6.2 68 14.9 7 May 4.8 58 14.7 9 May 15 Feb 0 5.8 69 15.4 8 May 4.7 61 15.4 9 May 15 Feb 40 6.1 71 16.1 8 May 5.1 66 15.6 10 May 15 Feb 66 6.2 77 16.7 8 May 5.7 70 17.2 10 May 1 March 0 5.6 69 15.9 8 May 4.9 61 16.4 11 May 1 March 40 5.9 68 15.6 11 May 4.8 64 15.4 11 May 1 March 96 5.8 74 16.4 11 May 5.9 71 16.9 13 May Cu= Col d unit percentage of first quality fruits and moreover gave an earlier mean harvest date. For each starting date, the combination of illumination and low temperatures gave the highest production and the best quality. Economics and Farm Management Analysis Economic calculations on high-density plantings M.J. Groot Economic calculations on high density apple plantings In the experimental orchard at Zeewolde and the Research Station in Wilhelminadorp, a trial with high-density plantings of apple was planted in 1991. The planting densities of 74 the trial vary between 3,000 and 20,000 trees per hectare (see also page 25). The results of the first four years of the trial (with the cultivar Jonagold) were used for economic calculations. These calculations are based on the complete expected lifetime of the plantings. Some data needed for the calculations were not available, such as data for future years or data on labour. Such data were taken from earlier research or from the standards published in "Kwantitatieve Informatie", a brochure from the Fruit Production Division of the National Reference Centre for Arable Farming and Horticultu re. The assumptions for the calculations will be described first. Assumptions calculations The comparison between plantings is based on the gross margin (see below). Therefore costs for fixed labour were left out of the calculation. The cost for casual labour was assumed to be fl 16.00 per hour. The lifespan was assumed to be shorter as the density increased (Table 51). Table 51. Assumptions and data for different planting densities Planting density 3,000 6,000 10,000 20,000 Life-cycle (year) 12 10 8 8 Production (tonnes/ha) - year 1 3.8 8.2 14.7 31.5 - year 2 27.4 42.9 56.6 78.4 - year 3 46.3 89.6 117.9 124.3 - year 4 61.4 86.4 103.3 111.0 - future years 50 75 88.75 105.5 Average price Guilders/kilo 0.90 0.90 0.85 0.80 The four-year average auction price for Jonagold was fl 0,88 per kilo. Because of the long life cycle (an average price of fl 0,90) was chosen for the plantings with 3,000 and 6,000 trees per hectare. Production from the more intensive plantings suffered more quickly from a decrease in quality. The more intensive the density, the greater the part with poorly coloured fruit. For this reason the production from the two plantings with the highest density was valued at lower average prices. Besides this difference in the average prices, the assumption has been made that all plantings will give more low quality fruit during the last quarter of their life-cycle and therefore will receive a lower average price of 5 cent per kilo. The average prices are used for the total production and for all years of the planting. The calculations were made with the so-called investment model. Calculated were the net present value and the annuity of the net present value (ANPV). These are based on the gross margin, which means the returns minus only the direct costs of the planting. The value of all gross margins in the different years was calculated for the year of investment and then summated (present value). This present value, minus the costs for the investment, gives the net present value. Because the plantings have a different life span, the ANPV was calculated. This is the net present value divided by the years of the planting. 75 Resu/ts The ANPV of the system with 6,000 trees per hectare was the highest. At a density of 20,000 trees per hectare the planting had a negative ANPV. This means that this planting has not covered its costs during its lifetime (Table 52). Calculations were also made for different values of some variables, to clarify the effect of such variables on the ANPV. The cost of the trees is one variable. A lower price per tree gives a higher ANPV. A lower tree price did not make much difference. The ANPV Table 52. ANPV (guilders/ha) for the various planting densities. Planting density 3,000 6,000 10,000 20,000 ANPV 6.481 8.771 1.328 -7.765 at a price of fI 3.50 per tree for the density with 10,000 trees per hectare was still lower than the ANPV of the 3,000 trees density with the standard tree price of fl 5.62 per tree. The ANPV of the 20,000 trees density remained negative at a tree price of fl 3.50 (Table 53). Table 53. ANPV (guilders /ha) for different planting densities (trees/ha) with different prices per tree (guilder/tree) Density Tree price 5.62 5.50 5.00 4.50 4.00 3.50 3,000 6,481 6,523 6,697 6,871 7,045 7,219 6,000 8,771 8,866 9,264 9,662 10,060 10,458 10,000 1,328 1,518 2,307 3,096 3,886 4,675 20,000 -7,765 -7,386 -5,808 -4,229 -2,650 -1,072 Table 54. ANPV (guilders/ha) for different planting densities (trees/ha) and diffe rent prices for Jonagold (cents/kilo) Density Price Jonagold* 70 80 90 100 110 3,000 -1,738 2,372 6,481 10,591 14,701 6,000 -3,701 2,535 8,771 15,007 21,243 10,000 -13,658 -6,165 1,328 8,821 16,314 20,000 -25,589 -16,677 -7,765 1,147 18,971 * Averaged prices for the planting with 10,000 en 20,000 bomen/ha the prices were taken 5 and 10 cents/kilo lower respectively. 76 The price per kilo is another variable and had a stronger influence on the ANPV (Table 54). With an average price of fI 0.80 per kilo, the ANPV of the density with 3,000 trees per hectare was higher then that of 6,000 trees per hectare. The ANPV of 20,000 trees per hectare only became positive when the average price for Jonagold was higher than fl 1.00. As stated earlier, the quality of the production may differ between the various densities. The trial showed differences in quality even between 3,000 and 6,000 trees per ha. If these differences prove to be greater in practice, this will certainly have an effect on the average price. If the planting with 3,000 trees commands a higher average apple price than the planting with 6,000 trees, the profit from the higher density will soon disappear. If the average price from the production of the 6,000 planting drops from 90 to 85 cents per kilo, the ANPV of the 3,000 trees planting will already be better than that of the 6,000 trees/ha. A sensitivity analysis was made for the variables "lifetime", "quality" and "production". If all plantings should have a lifetime of 12 years, it would make no difference for the choice between the densities. Similarly the assumption that the quality of production is lower at the end of the lifespan, had no effect on the results from the planting densities. The production level proved a very important variable. A lower production lowers the ANPV (Table 55). If production of a 6,000 density in practice is only 90 % of that obtained in the trial, the ANPV of the planting with 3,000 trees per hectare, with a production similar to the trial results, would have been better. Table 55. ANPV (guilders/ha) of 4 planting densities (tress/ha) at lower production levels (tonnes/ha, 100 % = production level of the trial) Production level (%) Density 100 90 85 3,000 6,481 5,195 4,549 6,000 8,771 6,771 5,771 10,000 1,328 -720 -1,720 20,000 -7,765 -9,763 -10,763 Conclusion The calculations given above, show that plantings with densities of 10,000 or 20,000 trees per hectare are not profitable with the above assumptions. Of all variables, the price per kilo of Jonagold had the biggest effect on the ANPV. Given the average price paid for apples during the recent years, the optimum planting density will have been between 3,000 and 6,000 trees per hectare. Economic calculations on high-density pear plantings M.J. Groot, J. Goedegebure, H. Wullems (trainee) Similar calculations to those made for apple plantings, were also made for pear. For these calculations more trials were used. The planting densities in these trials, with the cultivar Conference, varied from 2,000 trees to 4,000 trees per hectare. One of the 77 most important variables proved to be the price per kilo of Conference. This was set at fl 1.05 per kilo as an average price for the coming period. This price is an average for all the kilo's produced during the lifetime of the planting. The trials which formed the basis of the calculations differed greatly in production level; this was caused by dif ferent years of planting and different locations. Therefore, the production used for the calculation was not based on the counting average of the trials. For each trial, the production level of the various planting densities was related to the production level of the planting with a density of 2,000 trees per hectare. The average of all these relative production levels formed the basis for the production level used. The production of the density with 2,000 trees per hectare was taken as 100 % (standard). Higher densities produced an increase in production, especially in the first years of the planting (Table 56). Table 56. Production (tons/ha) of various planting densities (trees/ha) of Conference on Quince MC. Year Density 2,000 2,500 3,000 3,500 4,000 1 0 0 0 0 0 2 0 0 0 0 0 3 6.0 7.1 8.1 9.2 10.2 4 16.0 17.7 19.5 21.2 22.9 5 26.0 28.5 31.1 33.6 36.2 6 31.0 32.8 34.7 36.5 38.4 7 36.0 37.4 38.7 40.1 41.4 8 42.0 43.1 44.1 45.2 46.2 The production from the adult planting is considered to be equal to that obtained in the 8th year. Results The annuity of the net present value (ANPV) was calculated like in the same way as for apple. The conclusion is that the ANPV slowly increased with increasing density, but the difference in ANPV between 2,000 and 4,000 trees per ha was very small. Intensification of the planting density of pears does not seem to have good prospects. The calculations were made for normal trees with vertical trunks. In 1995, more atten tion will be given to the V-trellis of pears (trees with oblique trunks), Table 57. Table 57. ANPV (guilders/ha) at various densities (trees/ha) of pear plantings. Density 2,000 2,500 3,000 3,500 4,000 ANPV 9,649 9,664 9,687 9,724 9,740 78 Effect of light in intensive orchards M.J. Groot Combination of light model and investment model A combination of the light model (developed by P.S. Wagenmakers) and the investment model (developed by J. Goedegebure) has been made. With the combined model, it is possible to make an estimation of the technical and economic results of a given planting system. The combination model first calculates the maximum physical production of a planting system, according to the light interception of the system. Next, the economic results of the planting are calculated. The advantage of the combined model is that, before a trial or orchard is being planted, an informed choice can be made between the various planting systems. In 1995 a comprehensive description of the model will be produced. Prediction of optimum picking time of pome fruit M.J. Groot, A.J.P. van de Waart (IKO Relation price-quality for Elstar and Jonagold Large price differences between apples of quality grades I and II have existed for a long time. Fruit that is sold at auction as a combined lot comprising products from several growers is not only classified according to fruit quality, but also according to various colour classes. These classes are based both on the background colour (green, green/yellow or yellow) and on the blush (10-33 %, 20-50 % and more than 33 %) of the apples. Our project aims to clarify the possible price differences within a certain quality class, caused by the difference in the colour class of the fruit. Method Two auctions possessed data on prices as described earlier. Unfortunately they were based on different periods for auction 1: 1993 and the first half of 1994, and for auction 2: only the first four months of 1994. The cultivars involved were Elstar and Jonagold, size 70-80 mm of quality class I. Auction prices differed per season, the time during the season, demand and supply. To make sure that the differences in price were caused by colour and not by daily price fluctuations the calculation was made with relative prices. For every auction day the average price was calculated for quality class I. Next, the prices of the different colour classes were related to this average price. For the whole period the relative prices for a colour class were averaged (Table 58). Results For both cultivars the results show the same trend: apples of a green colour and with a large amount of red blush can command a much higher price than average for quality class I. Apples with a yellow colour are always of a lower value than apples with the 79 same amount of blush but with a green or green/yellow ground colour. Based on these results it was decided that in 1995 this work will be continued with national data, a longer period, more cultivars and different sizes. Table 58. Relative prices of Elstar and Jonagold, quality class I, size 70-80 and different colours. Ground Blush colour Elstar Jonagold 1 2 3 1 2 3 1 78 102 110 79 106 118 2 79 94 102 79 96 110 3 55 72 77 - 79 82 * ground colour 1 = green, ground colour 2 = green/yellow, ground colour 3 = yellow blush 1 = 10 - 33 % red, blush 2 = 20 - 50 % red, blush 3 = more than 33 % red Effects of agricultural and environmental policy on fruit industry M.J. Groot In 1990, an experiment was begun at two experimental gardens (Numansdorp and Zeewolde), to develop an economical production of apple, minimizing the undesirable side-effects of the use of chemicals (pesticides, fertilizers). At each location a comparison was made between three systems of fruit growing: I = current, II = integrated and III = natural. The technical aspects and results of the trial are described on page 116. The three systems are compared here economically. Only differences in costs and returns, directly related to the systems, were taken into account. For costs this means only costs for labour and for crop protection. Table 59. Costs and results (guilders/ha) at prices averaged over four years three systems at two sites in 1994 Numansdorp Zeewolde System* I II III I II III Returns 43.649 43.535 41.533 45.730 46.601 45.020 Costs Fixed labour 9.608 8.697 10.609 12.273 12.999 13.262 Cas. labour 12.260 12.175 11.734 13.668 14.529 14.526 Crop prot. 2.051 2.225 1.573 1.240 1.390 1.291 Results 19.730 20.438 17.617 18.549 17.683 15.941 I = current, II = integrated, III = natural 80 The production from the three systems was divided into various quality classes and these were multiplied with the average price per kilo for that quality. This was done with two different prices: the real price in the specified year of production and a price averaged over several years. The costs of labour include costs for fixed and casual labour. All labour for cultural activities and 10 % of the picking and grading work was done by fixed labour (fl 33.00 per hour). The rest of the picking and grading work was carried out by casual workers (fl 16.00 per hour). The costs for crop protection include the costs for pest, by casual disease and herbicide control, fertilization and growth regulation, natural system (III), stable manure was used at planting and, in Numansdorp alone, soil cloth. This soil cloth was laid in the second year of the trial. This is not normal. Therefore in the calculations, it has been assumed that the soil cloth was laid before planting. Because of insufficient knowledge of the life of the material, the complete costs of the material were calculated in the first year of the planting. Results The results of the calculations have been averaged for the eight cultivars in the trial Table 59 (prices averaged over several years) and Table 60 (real price). Table 60. Costs and results (guilders/ha) at real prices for three systems at two sites in 1994 Numansdorp Zeewolde System* I II III 1 II III Returns 34.935 34.590 32.563 36.214 37.162 35.934 Costs Fixed labour 9.608 8.697 10.609 12.273 12.999 13.262 Cas. labour 12.260 12.175 11.734 13.668 14.529 14.526 Crop prot. 2.051 2.225 1.573 1.240 1.390 1.291 Results 11.017 11.493 8.647 9.034 8.244 6.855 * I = current, II = integrated, III = natural The results are expressed as the difference between the returns and the costs for labour and crop protection. In 1994 the results of the current (I) and the integrated (II) system were nearly the same. The natural (III) system was clearly lower. Table 61 gives the total results from 1990 to 1994. These total results are calculated from the returns from 1991 to 1994 and the costs for labour and crop protection from 1990 to 1994 and the extra costs for planting the natural (III) system (soil cloth in Numansdorp and stable manure at both locations). Table 61 shows a great difference in the economic results between the three systems. The current system gave a far better result than the other two systems. In the first three production years the result of the natural (III) system was reasonably good when compared with both of the other systems. If the results of the system (III) in 1994 had been good, the higher costs at the beginning might have been compensated and the system as a whole would have achieved good results. However, the results in 1994 81 were not that good and when 1994 is representative for coming years, the natural (III) system will give the poorest results. It may be possible that the difference between the current (I) and the integrated (II) system will become smaller in the future. The data in the tables are averages for the eight cultivars in the trial. Looking at the cultivar effects, Zeewolde showed for each cultivar the same trend between the systems as the averaged data. In Numansdorp some of the cultivars deviated from average. Elstar in the natural (III) system showed a better result for the years 1991- Table 61. Total results (guilders/ha) of the three systems in two sites for the years 1990-1994 Numansdorp Zeewolde System* I III [H I M III For averaged prices 29.134 21.896 16.780 46.928 43.167 29.146 For real prices 12.533 6.550 533 21.525 13.771 1.203 * I = current, II = integrated. III = natural 1994. When the first year is taken into account as well, the natural (III) system with Elstar was second best, and the current (I) system was the best. The same holds for Cox's O.P. For Jonagold the integrated (II) system gave the best results. Alkmene and the CPRO number 78039-19 (Ecolette) both, had the best results in the natural (III) system, looking at the production years 1991-1994, but there was no difference between the three systems when looking at the whole period of 1990-1994. The results of Rode Boskoop were best in the natural (III) system (FL 26,936 for 1990- 1994) and were the worst the current (I) system (fl 5,448). The reason for the differences between Zeewolde and Numansdorp might be that the natural (!) system in Numansdorp was planted on former pear land and the other two on former apple land. The reaction to soil history varied with each cultivar. Rode Boskoop at Numansdorp has shown great differences in production in the different years under the current (I) and the integrated (II) systems but not under system III. It is unknown why this biennial bearing did not take place in the natural (III) system. The trial in Numansdorp was ended prematurely, because the garden was closed for financial reasons. It may have been that a sound economic system could have been developed for Rode Boskoop with low chemical input. For the other cultivars it seems that the current system would have remained the best economically. This conclusion is only true if no price differences exist between the apples from the various systems. If apples grown in the natural system command a higher price, in an "environment trade", the conclusion might be different. For Zeewolde the required difference in price must be at least 11 cent per kilo. This is obtained by dividing the results of fl 17,782 (averaged prices) by the total production of the natural system = 157.6 tonnes. The natural system in Numansdorp needs at least 10 cents/kilo more to equal system I. 82 Decision support systems in fruit growing M.J. Groot, J. Goedegebure, P.AM. Besseling (IKC), J. Bremmer (trainee) In 1994, the development of a farm model was continued. With this model the economic results of a holding can be calculated and also the effects on the environ ment. The model is intended for apple and pear plantings. Because these plantings are of a perennial nature, the model can make calculations up to 30 years. Most of the data, necessary for the model are obtained from "Kwantitatieve Informatie" a brochure of the Fruit Production Division of the National Reference Centre for Arable Farming and Horticulture (IKC). In the model crop protection is emphasized. For the calculations one can choose between three production systems, the same as described on page 116. The three systems are: the current production system (crop protection), an integrated system which is in use on some farms and a natural system which, until now, was only been used in experiments. The model calculates the following data: fruit returns, total business returns (including non fruit), costs, net trading results, investments, profitability, liquidity, savings, solvability, own capital, farmers income and labour hours. As far as the environment is concerned, the model calculates: use in kilo active ingredients (index for governmental policy), spraying index (quantity used divided by the quantity advised by the Extension Service), and the results on the "environmental" for water life, soil life and ground water in spring and in autumn. This last index has been developed by the Centre for Agriculture and Environment and gives for every chemical the environmental risk". First of all it is an index to compare various chemicals. Because the environmental risk depends on the soil, the index distinguishes soils with five different contents of organic matter. The model has a special importance for crop protection. For 1995, the aim is to adapt the model to include additioned components such as labour. Initial calculations show that the model is a good instrument to illustrate the effects of certain regulations (such as governmental policies) or measures (such as the use of tunnel sprayers). * yardstick from pesticide " in environmental impact points 83 Plant Nutrition and Fruit Quality Physiology Fruit ripening as affected by environmental factors during the growing season J. Tromp Theeffect of temperature later in theseason onsome of theripening andquality criteria in apple. Based on an experiment on Cox's Orange Pippin in 1992 (Annual Report 1992, p.82) it a tentative conclusion was reached that fruit ground colour around harvest was affected by the temperature during the first eight weeks following full bloom. The temperature later in the season was of little importance in this respect. In 1993 Elstar trees were exposed to 16 °C, 20 °C or 24 °C during the first six weeks following bloom (Annual Report 1993, p.88-89). Thereafter, until harvest, the tempera ture was 20 °C in all cases. All ripening and quality criteria involved in the experiment Dolour value 15 10 5 : —i— 20/16oC 0 •". -A- 20/20OC -5 -10 20/24OC -15 ^ -&€^^ -20 i i i i i i i I -zo 12 13 14 15 16 17 18 19 20 Weeks after full bloom Figure 7. Fruit firmness around picking time as affected by exposure to different temperatures from six weeks following bloom. 84 „ _ Firmness (kg) 10 r 4 9 A 8 7 ^ \ "A A —I— 20/16oC 6 "A 5 A 20/20OC 4 - A —&~ 20/24OC 3 - 2 1 0 I I I I I I I | 12 13 14 15 16 17 18 19 20 Weeks after full bloom Figure 8. Ground colour of fruits around picking time as affected by exposure to different temperatures from six weeks after bloom. About -20 and +10 correspond with hard-green and completely yellow, respectively. (e.g. firmness, ground colour, starch value) produced as marked response to the temperature early in the season. As a logical continuation of the latter experiment, a new experiment was carried out in which potted Cox's Orange Pippin trees were exposed to the same day-temperature of 20 °C. In the remaining part of the season, until harvest, the day-temperature was 16 °C, 20 °C or 24°C . Night temperature was 4 °C lower throughout; day length was 14 h. The vapour pressure deficit of the air was the same at all temperatures. Soil temperatu re was about 16 °C throughout. From 13 weeks after full bloom (i.e. 4-5 weeks before "normal" picking time), for eight weeks, a number of fruits were picked weekly. Immediately after picking the following parameters were recorded: fresh weight, specific weight, height and diameter, ethylene production, ground colour, firmness, starch value, sugar content, acid content and degree of bitter pit occurrence. In addition analyses were carried out for Ca, Mg and K. The results support the conclusion of the experiment carried out in 1992. In general, the effect of the large differences in temperature given in the second part of the season on the various ripening and quality criteria was small. For fruit firmness this is illustrated in Figure 7 and for ground colour in Figure 8. The difference in firmness was only slight between 20 °C and 24 °C, but fruits grown at 16 °C were clearly firmer than at the higher temperatures, especially when picking was delayed. There was no difference in ground colour between treatments; the three lines fall together. From the three experiments done so far it may be concluded that the temperature 85 during the first few weeks following bloom (May-June) has a very important effect on the ripeness of the fruit around harvest time and, thus, on the time of picking. Thereaf ter, later in the season (July-August), temperature is a much less important factor. Lateral shoot formation in young fruit trees in the nursery phase J. Tromp and S.J. Wertheim Lateral shoot formation in apple in the first year after budding as affected by soil temperature in relation to time of year J. Tromp As a continuation of previous experiments (e.g. Annual Report 1993, P.89-91) bud- grafts (rootstock M.9) of cvs Elstar and Rode Boskoop were exposed to a low (12 °C) or a high (22 °C) soil temperature in each of three successive periods of about six weeks. There were four treatments, i.e. 22-22-22 (in period 1, 2 and 3, respectively), 22-12-12, 12-22-12, and 12-12-22. Air temperature was (day and night) 21 °C; day lenght was 14 h. Air humidity was 80-85 %. Since the pattern in the data did not show important differences between the two cultivars, results for Rode Boskoop only are given in Table 62. The effect of the various treatments mainly concerned the lateral shoot growth and to a much lesser degree the growth of the main shoot. The high soil temperature in period 1 enhanced growth of the main shoot in that period but reduced growth in period 2 as compared with a low temperature in period 1. Main shoot growth in period 2 did not respond to the tempera ture applied in that period. Apart from the low value at 22-12-12, growth in period 3 was the same at the various regimes. Table 62. Growth of Rode Boskoop in each of three successive periodes of the growing season as affected by a low or a high soil temperature Soil Main shoot Lateral shoots temperature 1 2 3 1 2 3 °C 22-22-22 74b 30a 11b 85a 11a Oa 22-12-12 77b 27a 4a 110a 10a Oa 12-22-12 65a 46b 17b 50a 104b 11a 12-12-22 67a 44b 17b 82a 116b 11a Values within a column followed by different letters differ significantly (P= 0,05) . With respect to lateral shoot growth the data suggest a reduction at 12 °C in period 1. There was a pronounced carry-over effect of the temperature given in period 1 on growth in period 2, resulting in a much stronger growth at 12 °C than at 22 °C (given in period 1), whereas the actual temperature in period 2 again was not of any importance. 86 In period 3 growth activity was low. There were no differences between treatments. Most surprising is the predominating influence of the soil temperature in the first period of the growth season. The detailed data on the distribution of the lateral shoots over the main shoot as affected by the various treatments will not be discussed here. The effect of air- and soil temperature on compatibility of a few pear cultivars on rootstock Quince MC J. Tromp and S.J. Wertheim In order to find out whether the problems occurring in the compatibility of pear on Quince MC may be related to weather factors, bud-grafts of cvs Doyenné du Comice and Conference on Quince MC were exposed to a different combinations of air and soil temperature. There were two soil temperatures, 14 °C and 22 °C. The low soil tempera ture was combined with day/night air temperatures of 16/12 °C, 19/15 °C, 22/18 °C, and 25/21 °C, and the high soil temperature with 19/15 °C, 22/18 °C, and 25/21 °C. The results showed a considerable spread. The percentage of more or less successful bud-grafts of Doyenné du Comice exceeded that of Conference (Table 63). The force needed to break the graft-union might be higher at the high than at the low soil temperature. There was no clear pattern in the effect of air temperature on the breaking force. It is not surprising that shoot growth and breaking force give a positive correlati on positively. Table 63. The effect of air and soil temperatures on the percentage of successful bud-grafts, the mean shoot growth per tree and the mean force per tree needed to break the graft-union of Doyenné du Comice and Conference on Quince MC. Temperature °C Doyenné duComic e Conference Day/night Bud-grafts Growth Breaking Bud-grafts Growth Breaking force force air soil (%) (cm) (kg) (%) (cm) (kg) 16/12 14 93 78 16.2 64 55 11.6 19/15 14 71 26 8.6 64 41 7.4 22/18 14 79 20 5.2 64 48 10.5 25/21 14 79 30 10.9 64 102 22.3 19/15 22 79 65 25.1 64 77 17.1 22/18 22 86 120 23.6 64 112 20.4 25/21 22 79 102 25.0 64 134 27.7 87 SoffScience andPlant Nutrition Optimum storage conditions and the suitability of storage techni ques for fruit. F.P.M.M. Roelofs, E.A. van Hermon and A. Scholten Doyenné du Comice Aim In 1991, '92 and '93 at Wilhelminadorp and Numansdorp research was carried out to determine the possibilities of CA-storage on Doyenné du Comice. The aim of CA- storage was to prolong the storage period and to improve the quality. Method In 1991 at Wilhelminadorp the effect of crop load and harvest date was examined. Fruits were stored in regular storage and at combinations of 2 % oxygen and 0.2, 1 and 2 % carbon dioxide at -0.5 °C as well as at -1.5 °C. This research was carried out in containers of ± 1 m3 in Wilhelminadorp. Because of heavy losses caused by freezing injury during storage at -1.5 °C and internal browning during storage at 2 % carbon dioxide all combinations with -1.5 °C or 2 % carbon dioxide were skipped in 1992 and '93. In 1992 the research was carried out in small storage rooms at Numansdorp. in order to examine the effect of different storage systems, some of the research was duplicated at Wilhelminadorp in the storage containers but no differences were found. In 1993 the experiment was replicated at Wilhelminadorp. The harvest dates were: 6 and 13 October 1991, 22 and 29 September 1992, 16 and 23 September 1993. Fruits were taken from storage and assessed for quality in the first week of January, in the second week of February and in the second week of March. After six days of shelf-life at 10 °C the quality was assessed again and also after two and four days at 20 °C. Results At removal, pears from the first pick were firmer than those from the second pick. In February fruits stored in regular storage were less firm than fruits stored in CA-conditi- ons (Figure 9). In January, pears stored under regular conditions softened quickly during the first phase of shelf-life. In March those fruits softened rather slowly. After long-storage the fruits were not juicy. Figure 9 shows the first indications in February of irregular ripening during shelf-life. Differences between the two CA-conditions were not significant. Pears were less green after long storage. At removal pears were less green in March than in January and February. The colour of the pears hardly changed during the first six days of shelf-life in January whereas it changed rather rapidly during the same period in February and March. Over-ripe pears were found in all seasons. In 1991 the problems were only small (average = 2 %), in 1992 they were great (average = 18 %) Over-ripeness increased rapidly during shelf-life. At removal 2.5 % of the fruits were over-ripe, after six days 6 88 Firmness in kg Shelf-life period in days R CM CA2 R CA1 CA2 R CA1 CA2 R=regular storage CA1= 2%02-0.2%C02 CA2= 2%O2-1.0%CO2 Figure 9. Firmness of Doyenné du Cornice during storage % and after ten days 30 % of over-ripe pears were found. During shelf-life over- ripeness was mostly found in early-picked pears. Regular stored pears were most susceptible to over-ripening. Comparing both CA-conditions less over-ripeness was found in pears stored at low carbon dioxide concentrations. Figure 10 shows that over- ripeness was never found in January while 30 % over-ripeness was found in March. Fruits of almost all origins were susceptible to browning in the core. Usually only the pith was brown. In only a small number of cases the fruit-flesh was attacked. Browning was found in January in fruits of all examined storage conditions. Regular stored fruits were less susceptible at removal, but after shelf-life most browning was found in these pears. Comparing both CA-conditions more browning was found in pears stored at high carbon dioxide concentrations. Conclusions - CA-stored Doyenné du Comice is firmer and greener than regular stored Doyenné du Comice - Doyenné du Comice is not juicy after long storage (February / March) - Over-ripe pears were found in February first, especially after shelf-life - Browning of the core is a problem after long storage 89 percentage over-ripefruit s Shelf-life period in days 110 J8 l6 h K CA1CA 2 K CA1CA 2 K CA1CA 2 R-Regularstorag e CA1- 2%02-0.2%C02 CA2= 2%02-1.0%CO2 Figure 10. CA-storage at Doyenné du Cornice - Doyenné du Comice keeps best during storage at -0,5 °C, 2 % oxygen and as low a level of carbon dioxide as possible - In any storage condition there are big risks of quality loss after February Red, pink, and white currants F.P.M.M. Roelofs Storage of red, pink and white currants has changed considerably since 1991. Results of storage trials with a small number of varieties resulted in global advice on storage conditions, harvest dates and storage periods. In practice there is a need to know which varieties are most suitable for storage. Aim The aim of the storage experiment in 1994 was to examine which varieties are suitable for storage. 90 Methods In Wilhelminadorp twelve red, one pink and four varieties of white currants (Table 64) were harvested one week after they have been totally coloured. The currants were stored at 0 °C and 20 % carbon dioxide at 2 % as well as at 16 % oxygen. Fruits were picked from young bushes as well as from old bushes for a small number of varieties. Results On 15 November 1994 and 3 January 1995 all varieties were assessed for currant quality, stem quality and general aspects at removal and after four days shelf-life at 18 °C. Taste and gloss were important beside mouldy currants. Late-ripening varieties could be stored better. Firstly these cultivars are picked later (and stored for a shorter time), secondly it is possible that such varieties have better storage potential. Table 64. Harvest-scheme and general assessment after storage at 0 °C and 20 % carbon dioxide. Variety Harvest date General assessment after storage and shelf life 18 November 6 January Red currant Rolan 13 July satisfactory bad Stanza 13 July satisfactory bad Detvan 20 July satisfactory bad Rotet 20 July bad bad Rovada 20 July satisfactory bad Tatran 27 July bad bad Cassa 27 July satisfactory moderate Rode Rebel 3 August bad moderate Rondom 3 August satisfactory reasonably Roodneus 3 August well satisfactory Augustus 17 August well satisfactory Heinemans R.S. 31 August satisfactory moderate Pink Currant Rosa Sport 20 July satisfactory bad White currant Witte Parel 20 July satisfactory bad Albatros 20 July bad bad Primus 20 July satisfactory moderate Blanka 27 July satisfactory bad In general the storage results of currants from young bushes were worse compared to those of old bushes. Stalks of Rotet were coloured red at the first assessment, especially stalks from young bushes. 91 Conclusions - Currants from young bushes do not store well -None of the pink and white cultivars were suitable for long-storage. Superficial scald on Jonagold H. de Putter Research took place in 1993-1994 to establish how different factors affect the occurrence of scald and to see if measuring or determing those factors during the first months of storage can give an indication of scald occurrence after eight months of storage. Also influence of harvest date and storage condition on scald occurrence was investigated. Experiments in Israel showed a reduction in scald occurrence when Granny Smith apples were heated for two or four days at 38 °C directly after picking. For this reason we also investigated the possibility of heating Jonagold apples for 2 days at 38 °C in order to reduce the occurrence of scald after eight months of storage. Jonagold apples were picked at four locations in the south-west region of the Nether lands. A first pick (early) took place ten days before optimum harvest date for long ULO storage. The second pick (normal) took place when optimum harvest date was reached. Apples were stored at 3 % oxygen and 1 % carbon dioxide (HOLC) or at 1.2 % oxygen and 5 % carbon dioxide (LOHC). Immediately upon removal from storage firmness, fruit weight, ground colour (L*a*b values), brix %, acid % and different biochemical compounds were measured. The biochemical compounds probably influence scald occurrence. Scald is probably caused by an oxidation process of alpha farnesene (AF) to conjugate triterpene hyperoxides (CTH's). Risk of scald occurrence would be greater as a result of high levels of those compounds. On the other hand this oxidation process is inhibited by anti oxidants. The total anti-oxidant amount was measured as optical density 205 (OD 205). Vitamins E and C are also anti-oxidants. Content of those two vitamins was also measured. Early- and normal-picked apples showed after storage at LOHC no incidences of scald (Table 65). Storage under HOLC conditions showed incidences of scald. More inciden Table 65. Scald % and quality on 31 May Condition Pick Treatment Scald Firmness Ground colour acid 1) kg/cm2 a*valu e % LOHC early none Oa 6.06 -14.09 0.38 LOHC normal none Oa 6.20 -12.86 0.39 HOLC early none 34 c 4.42 -12.34 0.34 HOLC early heat 69 d 4.67 -8.24 0.32 HOLC normal none 10 b 4.36 -11.27 0.34 HOLC normal heat 40 c 5.72 -6.14 0.29 1 ) numbers followed by the same letter are not significantly different from each other at p < 0.05. 92 ces of scald were present on early-picked apples compared to normal-picked apples. Also apples which were heated showed more incidences of scald in early-picked apples. Heating apples caused more incidences of scald instead of reduction. Apart from more incidences of scald on heated apples, a heat treatment also influences firmness, colour and acid level. Compared to untreated apples stored under the same conditions heated apples are firmer and show a more yellow ground colour and lower acid level. Storage conditions also influence firmness and colour. After storage in LOHC conditions, apples are more firm, show a greener ground colour and have a higher acid level compared with storage in HOLC conditions. Vitamin C is significantly lower in apples which were heated. Storage conditions and heating do not affect vitamin C content. Vitamin E seems higher in apples which were heated compared to non-heated apples. Total anti-oxidant (OD-205) is, after storage at HOLC higher compared to storage at LOHC. Also total anti-oxidant level is higher in normal-picked apples compared to early picked apples (Table 66). CTH level is higher in normal-picked apples which were stored at HOLC conditions compared with early- picked apples. When stored at LOHC conditions CTH level is lower in normal- Table 66 Content of different biochemical compounds. measured on 31 May Condi Pick Treat Vitamin Vitamin OD-205 AF CTH tion ment E2) C LOHC early none 13,59 14,03 a1) 26,72 a 12,91 a 1,16 a LOHC normal none 16,36 14,55 a 44,83 be 20,36 b 1,93 b HOLC early none 19,35 15,28 a 43,35 b 21,50 be 2,47 be HOLC early heat 21,50 7,88 b 54,61 d 26,69 cd 3,66 d HOLC normal none 18,84 13,43 a 53,49 d 20,36 b 1,97 b HOLC normal heat 21,64 8,13 b 63,98 e 27,18 d 2,67 c 1) numbers in a column followed by a same letter are not significant different from each other at p < 0.05. 2) Vitamin Ean d vitamin C content in mg/100 g fresh weight, OD-205, CTH en AF in nmol/cm2 apple peel. picked apples. While it looks as if those compounds influence occurrence of scald the content of those compounds was also measured after one, two and three months of storage in order to predict; the risk of occurrence of scald after eight months of storage. However a regression analysis showed no reliable relation between content of those compounds and occurrence of scald. This project was alsomade possible with fundsfrom Eurofru. 93 Reduction in fungicide use in spray scheme for controlling storage rot H. de Putter ULO storage of non-sprayed apples In 1993-1994 research was performed to investigate if storing non-sprayed apples is possible without more losses due to rot compared with normal sprayed apples. Non- sprayed apples were not sprayed during the last month before picking. Alternative non chemical rot controlling methods were also under investigation. In a first experiment sprayed and non-sprayed Elstar were stored under ULO condition until February 2, April 7 or April 22. Elstar was picked at three locations. Sprayed Elstar was mainly treated with Captan and Eupareen. Not every location had exact the same spray scheme. Apples were picked on September 6. After each storage period the percentage of rot was measured and the type of fungi which caused the rotting was identified. Botrytis and Pénicillium were at all observation dates the main cause of rotting (Table 67.) Table 67. Rot percentage in Elstar, average of all three ULO storage periods object Botrytis Pénicillium Gloeosporium Nectria rest Total sprayed 0,49 0,29 0,19 0,50 0,11 1,58 non-sprayed 0,97 0,55 0,34 0,67 0,37 2,90 F-test '> NS NS NS NS 1) NS, * ** #* * resp. not significant, P < 0.05, P < 0.01 and P < 0.001 This season less rot was present in ULO-stored Elstar compared with previous seasons. The percentage of rot in regular-stored Elstar was this season at the same level as previous seasons. Table 68. Effect of spraying on total rot in Elstar at differenl tstorag e periods February 2 April 7 April 22 average February 2 object ULO ULO ULO ULO Regular storage sprayed 1,36 1,56 1,83 1,58 2,31 non-sprayed 1,94 2,48 4,27 2,90 4,24 F-test v NS NS * * NS 1) see table 67 This season there was also a difference in the percentage of rot in sprayed and non- sprayed apples (Table 68). More rot, especially Botrytis rot, occurs when spraying is omitted. This difference is not very clear at the first two observation dates, but at the 94 Observation on April 22 there was a significant difference present. The average of all three observation dates also showed a significant difference. In a second experiment three different organic compounds, Algan 1 l/ha, Pilzvorsorge 5 kg/ha and Equisetum 5 kg/ha were compared with Captan 0.6 kg/ha, Eupareen 0.3 kg/ha and with non-spraying for their rot suppressing effect. From August 1 four weekly spraying with the organic compounds and Captan were carried out until one week before picking. Two weeks before picking Eupareen was sprayed once. Rot percentage was established after storage including three weeks' shelf-life at 20°C. In this test organic compounds were not effective in suppressing rot (table 69). In one case non-spraying showed better results than spraying with an organic compound. Table 69. Effect of organic compounds and chemical treatments on total rot in Elstar Eupareen Captan Equisetum Pilzvorsorge Algan non-sprayed rot % 1l 1,00 a 1,50 ab 2,95 c 2,10 be 2,06 be 1,84 b (P < 0.05) 1) Rot percentages followed by the same letter(s) do not differ significantly In a third experiment antagonists were tested for their rot-suppression effect. Antagonists are fungi, bacteria or yeast which can prevent rot growing by competing with rot-causing fungi or by producing antibiotics. Antagonists can be applied to the apples by drenching or spraying. In this test apples were drenched in a water solution containing spores of an antagonist. The following antagonists were tested: Binab T wp UF 10 g/l, Trichoderma sp. 1.107 spores per ml, Schaa-4283-03 2 g/l and NRRL Y- 18623 1.107 spores per ml. Results of rot-suppression by antagonists are not quite clear since no significant difference was present between the treatments. A significant difference was not even present between sprayed and non-sprayed apples. However it seems NRRL Y-18623 is the most promising antagonist in suppressing Botrytis and Pénicillium rot. Table 70. Effect of antagonists on rot in Elstar Binab Trichoderma NRRL Schaa sprayed non-sprayed Y-18623 4283-03 Rot % 3,49 2,85 2,48 4,03 1,56 2,48 In a fourth experiment periodic increases in the carbon dioxide level to 20 % over three days in ULO storage rooms were tested on rot suppression in Jonagold. In 1992-1993 it looked as if periodic increases of carbon dioxide at ULO storage could suppress rot. While the amount of rot was low with the treatments with carbon dioxide 95 and also with the control this effect was not significant. To obtain higher percentages of rot a similar experiment was carried out in 1993-1994 by storing apples in regular storage. Between the periods in which the carbon dioxide was increased apples were stored at 21 % 02 and 0 % C02. Carbon dioxide was increased every week up to a level of 20 %. This treatment was started in November or in February. Table 71. Effect of period carbon dioxide treatments on total rot % and carbon- dioxide injury in Jonagold C02 I " C02ll sprayed non sprayed Rot % at take out 1,3 0,7 2,0 6,5 Rot % after shelf life 6,2 9,8 6,2 14,4 C02 injury % 43,5 4,6 0,5 0,5 1) C02 I = Carbon dioxide treatments starting from November, C02 II = Carbon dioxide treatments starting from February Treating the apples weekly with carbon dioxide from November until removal from storage gave the lowest amount of rot (Table 71). Treating the apples from February until removal from storage showed more rot than the sprayed control which was not treated with carbon dioxide. When treated weekly from November until removal from storage 40 % of the apples are also injured by the carbon dioxide. When treated from February only 4.5 % are injured. This injury is only visible on the outside of the peel. The fruit flesh was not injured by the carbon dioxide treatments. This project was alsomade possible with fundsfrom Eurofru. Reduction of internal disorders during storage of Conference pear. Aim In co-operation with ATO-DLO, research on brown heart (cavities and browning of the fruit flesh) was started with Conference. The aim of this research was to find the cause of the problem and to set up a practical system for analysing the risk of brown heart. Method Orientation started in the season 1994-'95. An important part of this research was to find out the effect of origin and maturity on brown heart. During five weeks, starting on 9 September 1994, samples were taken from five orchards in the South-West of the Netherlands. Some growers had serious problems with brown heart in previous seasons. The pears were stored in regular storage and in three different CA-conditions until mid-January. Some of the pears were kept for two days at 20 °C before storage to increase susceptibility to brown heart, while others were put into storage immediately. Finally other pears were pre-cooled during 0 to 21 days before oxygen was removed to 2 % by flushing nitrogen to examine the effect of pre-cooling. 96 Results The treatments described above were effective in inducing cavities and browning of the fruit flesh. Initial results show a clear effect of harvest date. Cavities were found in 5 % of the pears from the first pick, averaged for all treatments, while this increased to more than 55 % in pears from the last pick. Browning of the fruit flesh was also affected by harvest date. The pears from different orchards showed various susceptibility to cavities. In pears from one site picked on 9 September, 20 % cavities were found, averaged for all treat ments, while in pears from another site picked on 20 September, 16 % cavities were found. It is still not known which factors have the greatest influence on these cavity occurrence. Over 10 % more cavities were found in pears kept for two days at 20 °C before storage compared with pears which were put in to storage immediately. The latter treatment appeared to have no effect on browning of the fruit flesh. Some indications were found of the effect of the pre-cooling period. In pre-cooled pears picked on 9 September 2 % pears with cavities were found after two days. Almost the same percentage was found in pears picked on 30 September and pre-cooled during 21 days. Slightly more over- stored pears were found in pears which were pre-cooled for a long period. No effect from the pre-cooling period was found with regard to colour and firmness. More browning of the fruit flesh was found under high carbon dioxide conditions. Browning of the fruit flesh was mostly found in combination with cavities but it was also found separately. Finally brown heart was also found in regular storage. In practice almost no brown heart was found in 1994. The research will be continued. Conclusions - Early picked pears are less susceptibile to brown heart - A non-cooled period increases the susceptibility to cavities - A long pre-cooling period decreases the susceptibility to cavities but increases the susceptibility to brown heart - Decreasing oxygen levels can not prevent cavities - Higher carbon dioxide levels during storage induce more cavities Skin spots on Elstar F.P.M.M. Roelofs Aim Skin spots on Elstar become an increasing problem during storage. Badly coloured fruits from a second and third pick are especially susceptibile. The aim of this research is to find factors which have an effect on skin spots. Storage conditions research at Geldermalsen and Wilhelminadorp In the seasons 1993-'94 and 1994-'95 research was undertaken to elucidate the effect 97 of storage conditions and storage periods on skin spots and quality in Elstar. Fruits from a second pick of six orchards were stored in Geldermalsen at 0.5 and 1.5 °C at 0.5 % as well as at 3.0 % carbon dioxide, all at 1.2 % oxygen. In 1994, the fruits were also stored in regular storage at 1 °C. In the first week of February and in the third week of March samples were taken from storage and brought to Wilhelminadorp. After one day quality was measured and the number of skin spots counted. Quality measurements were replicated after a week of shelf-life at 20 °C and skin spots were counted after two weeks of shelf-life. Results Less skin spots were found after storage at low temperature. The promotive effect of high carbon dioxide storage on more skin spots was found specially after storage at 1.5 °C (Table 72). To suppress skin spots it is better to store at the lowest possible carbon dioxide levels. The length of the storage period also had an effect. In March more skin spots were Table 72. Numbers of fruits with more than 1 cm2 covered with skin spots, stored at 1.2 % oxygen. The data are averages of recordings made at removal and after two weeks of shelf-life until the beginning of February and mid-March. Condition 1.5 °C 0.5 °C 0.5 % carbon dioxide 32.5 % 27.0 % 3.0 % carbon dioxide 50.3 % 33.1 % found than in February (Table 73). The differences after two weeks of shelf-life were less significant, while the number of additional skin spots increased more rapidly during shelf-life in February. During the season 1994/'95 it has been proved that skin spots develop in regular storage. The number of skin spots were comparable with the best ULO-condition (0.5 °C, 0.5 % carbon dioxide and 1.2 % oxygen). Table 73. Numbers of fruits with more than 1 cm2 covered with skin spots. The figures are average of storage at 1.5 °C and 0.5 °C and 3 % dioxide at 1.2% oxygen Storage period 1 day after storage After 2 weeks of shelf- life at 20 °C Beginning of February 19.3 % a 38.8 % b End of March 40.1 % be 44.8 % c Values followed by the same letter(s) do not differ significantly (P = 0.05) At lower storage temperatures fruits remained greener and firmer. In cases of high risk 98 at skin spots, it is best to store at low carbon dioxide concentrations in spite of the increased loss of firmness and background colour. In these cases fruits should be stored for a shorter period. These experiments have shown that factors such as storage temperature, carbon dioxide concentration and storage length can not totally prevent skin spots. At harvest, and after storage, samples of the fruits were analysed for quality, maturity and minerals. Some correlations were found between loss of weight during storage, background colour, sugar, calcium, and magnesium concentration and the proportion of dry-matter content with the number of skin spots. Using a correlative model including dry-matter content and magnesium concentration much of the variation in number of skin spots could be explained to a great extent. Positional effects In Numansdorp, Geldermalsen, Zeewolde and Wilhelminadorp the effect of cluster size, maturity and position within the tree has been examined. In each region fruits were harvested at two locations in a pick-through system on two times, with a one week interval. Both picks were made at the normal maturity stage and one week earlier. So, the second early pick was done on the same date as the first normal pick. Fruits picked from the east side were kept separate from those picked from the west side of the tree. In the same way fruits of different cluster sizes were kept separate. After harvest, the fruits were stored at Geldermalsen under conditions most likely to induce skin spots (1.5 °C, 1.2 % oxygen and 3 % carbon dioxide). Table 74 shows that the number of skin spots increased with later harvest. Also it is clear that skin spots developped mostly on fruits from the second pick. Fruits grown singly were less susceptible to skin spot than fruits grown in clusters. The number of fruits with more than 1 cm2 skin spots in April after two weeks of shelf-life at 20 °C rose from 14 % in fruits grown singly to 21 % for fruits grown in clusters of 3 or 4 fruits. No differences were found between fruits grown on the east side compared to those grown on the west side of the tree. Table 74. Percentage of fruits with more than 1 cm2 covered with skin spots 1 st pick 2 nd pick Early 4.9 a 7.4 a (1 week before normal) Normal 25.2 b 34.5 c (optimum harvest date) Values followed by the same letter(s) do not differ significantly (P = 0.05) Current advice: -Ensure sufficient light penetration into trees of susceptible orchards (for example by summer pruning) •Thin early and well (to one fruit per cluster) -Supply adequate magnesium and calcium 99 -Store susceptibe fruits at 0.5 °C, 1.2 % oxygen and as low as possible of carbon dioxide So/7Science andPlant Nutrition Control of growth and production of pit and stone fruit by water and nutrient supply M.P. van der Maas Advisory system for the water supply Transpiration The daily estimation of transpiration is an important aspect in WG-Meteo, an advisory system for the water supply. In the present version the transpiration is calculated according to Makkink (G.F. Makkink and H.D.J, van Heemst, 1967, De potentiële verdamping van kort gras en water, Annual book IBS: 89-96). It consists of the calculation of the so-called reference transpiration based on measured short wave incoming radiation and temperature. After multiplication with a crop specific factor (the crop factor) the potential transpiration is calculated in millimeters. In the case of trickle irrigation the so-called transpiration factor used expresses the amount of water in liters per tree. In WG-Meteo soil evaporation will be calculated independently from transpirati on. The transpiration factor equals a constant with the value 0.275 multiplied by the leaf area per tree in square meters (K. Kodde and J. Kipp, Meer zicht op waterverbruik appelbomen, Fruitteelt (1990)26:13-14). In order to test the transpiration calculation transpiration was measured for six two- year-old Jonagold trees on M.9 from July 8 untill August 28 with the stem heat balance method (F.P. Weibel and J.A. Vos, Transpiration measurement on apple trees with an improved stem heat balance method. Plant and Soil 166(1994)2:203-220). For the 35 days with continuous transpiration measurement, the calculated and measured transpi ration were compared. The average measured transpiration was 1666 ml per tree per day with extremes of 223 ml and 2904 ml. On 53 % of the days the deviation of the calculated transpiration was less than 10 %. On 82 % of the days the deviation maxim um was 20 %. On 18 % of the days the deviation was between 20 % and 60%. The weekly deviation ranged from 3 % to 23 % as positive and negative daily deviations partly compensated each other. Because of the high water buffer capacity of the rooted soil volume in comparison with the potential daily deviations only the accuracy on weekly basis is relevant. From the observations was therefore concluded that the tranpiration calculation according to Makkink is a promising method for the Dutch climatic conditions. The deviations can be explained by non-typical values for water vapour pressure deficit and/or wind speed that go along with the measured values for radiation and temperatu re. When these non-typical values exist for a longer period of time then the deviations will be higher than the maximum of 23% that was found here. In order to obtain maximum accuracy with the transpiration estimation the leaf area should be estimated too. In an orchard this can be done with light interception measurements. 100 Cropfactor for overhead sprinkling Kodde and Kipp indicate that the crop factors for full-grown apple orchards (assumed LAI of 2.5) range from 0.6 in the first ten days of May to 1.0 in the second decade of June when water uptake is not restricted (K. Kodde and J. Kipp, Watergift beter afstemmen op behoefte. Fruitteelt (1994)28:12-13). Soil evaporation was included in these crop factors assuming that 75 % of the évapotranspiration in the first ten days of May and 25 % from the second decade of June was soil evaporation. The transpiration of the grass strips was ignored. Implicitly it was assumed the trees fully profited from the applied water. The inaccuracy introduced with this assumption was studied with the simulation model SWATRE of the Winand Staring Centre for Integrated Land, Soil and Water Research in Wageningen, The Netherlands. In the grass strip, water is transpired by the grass while some water is taken up by tree roots. It is not known how many tree roots live in grass strips. It is evident however that the tree takes up most of its water from the tree strip. When the soil of the tree strip is drier than the soil of the grass strip, water will move from the grass strip to the tree strip. Finally when water uptake is restricted in a dry tree strip, relatively more water will be taken up by the tree roots in the grass strip. An important factor for evaluation is the magnitude of the difference in water content between the grass strip and tree strip. During the simulations the percentage of the extra water in the grass strip (relative to the tree strip) that the tree profits from is varied. With 100% utilization the water content of the soil of the grass and tree strips stay the same; with 0% utilization the water contents differ to a large extent. The percentage of utilization lies probably between 50 % and 100 %. This corresponded with crop factors of 1.65 and 1.34 respectively for an orchard with LAI of 3, tree spacing of 3.0 and 1.1 meter, a tree strip of 1.4 meter wide and a crop factor for grass of 0.8 (production grass has a factor of 1.0). According to the calculations of Kodde and Kipp this orchard would have had a crop factor of 1.15. From this it can already be concluded that the crop factors of Kodde and Kipp are to low and that research is needed on the utilization of grass strip water by the tree. An utilization percentage of the extra grass strip water of 75% seems to be the best estimate at the moment. For this utilization percentage, which corresponds with a crop factor of 1.50, simulation with SWATRE resulted in a mean soil water content over the first 70 cm of the soil column, averaged over the months July, August and September 1994, of 26 % for the tree strip and 30 % for the grass strip for a very light clay soil (12-16 % lutum, water content at field capacity 36 % and at wilting point 10 %, ground water level in winter 70 cm and in summer 190 cm below soil surface). Overhead sprinkling in this simulation was carried out to the point where water uptake reduction did not take place. The utilization percentage of 75 % resulted in the fact that 20 % of the water that the trees transpired during 1994 originated from the grass strip. From July to September this corresponded to 1 millimeter of water per day on the tree strip (1.54 square meters per tree). The horizontal water movement from the grass to the tree strip at the calculated difference in water content equalled 0.5 millimeters water per day through two boundary planes of 1.54 square meters in total. From this it can be concluded that in this situation from the 20 % of the water that was transpired by the tree and originated from the grass strip one half was taken up by tree roots in the grass strip and the other half first moved into the tree strip before the tree utilized it. This is acceptable as a first estimate. 101 Transpiration factor for trickle irrigation For calculating the amount of trickle irrigation that is needed the estimation of the fraction of water that is taken up from the trickle column in the soil is very important. When transpiration is fully compensated through trickle irrigation extreme leaching or drainage will take place. The volume ratio of trickle column versus tree strip volume is, with 1.5 to 2.0 square meters tree strip per tree 0.10 to 0.15. The uptake ratio will be higher (0.15 to 0.25) as the root intensity in the trickle column is higher. When uptake reduction takes place outside the trickle column the ratio will increase. In general the ratio will probably not exceed 0.50. Also in this framework the aspect of horizontal water movement will be a theme for further research. Improvement of the advisory system for fertilization, irrigation and soil management M.P. van der Maas Trace elements Sprays Sprays with Zinc at the mouse ear stage (1 liter Zinflow/ha) and Boron at the pink bud stage and during initial and full bloom (3 times 1 liter Bortrac/ha) in 1993 and 1994 did not result in increased production or better fruit quality in trials with Conference, Doyenné du Comice, Beurré Hardy, Beurré Alexandre Lucas and Boskoop at the research station in Numansdorp nor with Conference and Elise at the research station in Zeewolde. Variation in these trials however was such that only differences of 15 % to 20 % could have been shown reliably. The conditions for flowering were reasonable to good. It is therefore possible that under bad flowering conditions these sprays have considerable effect. From identical experiments with Jonagold, Elstar, Cox's Orange Pippin, Conference and Doyenné du Comice at other research locations for fruit growing in the Netherlands in 1994 the same conclusion was drawn. Sprays with Manganese at the pink bud stage and six and eight weeks after full bloom (3 times 1 liter Mantrac/ha) only had positive groundcolour effects in trials with Elstar and Doyenné du Comice (respectively 36 % and 20 % greener) but not in trials with Jonagold, Cox's Orange Pippin and Conference. The effect of Manganese was correla ted with the nitrogen content of the basal leaves of the long shoots in August. Elstar and Doyenné du Comice had 1.9 % and 1.7 % Nitrogen in their leaves. The Nitrogen content for Jonagold, Cox's Orange Pippin and Conference ranged from 2.2 % to 2.3 %. The positive effect of Manganese on groundcolour is possibly related to the nitrogen content. More research will be carried out on this matter. Boron fertigation Boron fertigation appears to be a good method to increase the boron level in the leaves of apple. In trials with Jonagold on M.9 and Boskoop on M.27 planted in ridges at 75 cm and 50 cm distance respectively with soil type marien calcareous very light clay, the boron content of the basal leaves of the long shoots in August could significantly be increased to 10 ppm with Jonagold and 6 ppm with Boskoop by increasing the Boron 102 concentration in the fertigation water from 16 mg to 216 mg Boron per cubic meter using Borax. This increase was realised in the first and second growth years. Averaged over the two years the Boron content in the leaves was 32 ppm for Jonagold and 24 ppm for Boskoop. Fertigation was carried out until the end of September in both years. The applied water volume was 112 liters per tree in the first growth year (76 up to mid- August) and in the second growth year 168 liter (105 till mid August). The boron content of the fruits in the second growth year was increased from 0.25 mg to 0.49 mg Boron per 100 g fresh fruit with Jonagold and from 0.24 mg to 0.37 mg with Boskoop. With an increase in the Boron concentration in the fertigation water to 56 mg Boron per cubic meter only an increase of the Boron content of the fruits could be detected with the exception of the leaves in the first growth year with Jonagold. The increased Boron uptake had no effect on the calcium uptake by the fruits. 103 Crop Protection Spraying Techniques Testing and development of application techniques in crop protection B. Heijne Emission to soil Emission to soil of two tunnel sprayers was compared with that of a cross-flow sprayer. grass lane Figure 11. The position of the filter cloths. 104 The Muckhof tunnel sprayer was developed from the IMAG-DLO principle,called OOSEF. The key priciple is the "Closed Loop System". The Joco tunnel sprayer was originally developed by Noric-Joco Spraying Systems. The company John continued the development with normal hollow cone nozzles. Trees were treated with the fluorescent dye Brilliant Sulfo Flavine (100 g/ 100 I) at the experimental orchard "Naar Beter Fruit" at Numansdorp. The trees were planted in a single row (3 x 1.5 m) and were planted in 1987. Before treatment, small shelves with filter cloth were laid on the ground (Figure 11). They were on the east and the west side of the tree row (under the trees) and in the middle of the grass lane. There were three positions with regards to the tree, viz. at the tree, half way between two trees and at a quarter of the distance between trees (Figure 11). Hence, there were nine filter cloths per replicate. Three replicates of filter cloths were placed in between one row and five rows were treated. The experiment was carried out twice, i.e. 21 July and 30 August 1994. __ % emission 50 r I LSD00 6 - 5.62 40 S „.<"" 30 / / 20 10 0 _L west middle east Figure 12. The average emission to the ground as the percentage of the actually sprayed quantity at three positions in the row for the cross-flow sprayer (•), the Joco tunnel sprayer (•) and the Munckhof tunnel sprayer (o) 105 There was no significant difference between the three positions with regards to the tree (P = 0.800; see table 75). There was a significant interaction effect between the type of sprayer and the position in the row (east, middle, west). Therefore the emission is plotted against the position in the row in figure 12. The same data are shown in table 76 after square root transformation. Table 75. The average emission to the ground after square root transformatior i as the percentage of the actual sprayed quantity. half quarter stem 4.105 4.111 4.004 Table 76. The average emmission to the ground after square root transformation as the percentage of the actual sprayed quantity. Position in the rows type of sprayer west middle east cross-flow sprayer 4.78 6.53 5.39 Joco tunnel sprayer 3.54 2.86 3.76 Munckhof tunnel sprayer 3.99 2.36 3.46 (LSD««» = 0.619) It is concluded that the position with regards to the tree had no effect on the amount of emission to the ground. The emission of the cross-flow sprayer was higher than that of the tunnel sprayers at all positions. The emission of the tunnel sprayers did not significantly differ from one another. The cross-flow sprayer had the highest emission in the middle of the grass lane, while the tunnel sprayers had the lowest emission in that position. Spray volume It is suggested that spray volume affects the efficacy of treatments. This has been demonstrated for the control of spider mites. A high volume treatment (1200 to 1500 l/ha) was more effective than low volume treatments (150 to 250 l/ha). Whether the spray volume also affects the control of scab (Venturia inaequalis) was tested at the experimental orchard "Midden Nederland" at Geldermalsen. Weekly treatments were applied to three year old trees of the cultivars Golden Delicious, Jonagold, Elstar, Schone van Boskoop and Cox's Orange Pippin. Treatments were 50, 75 and 100 % of the advised dosage of fungicides (e.g. standard rate 100 % of captan was 1.2 kg/ha). The trees were planted in a single row (3 x 1.5 m) and there were six replicates of five trees per cultivar. The two spray volumes tested were 100 and 200 l/ha. The treatments were applied with a Douven tunnel sprayer equipped with Noric rotary atomizers. 106 Table 77. The average percentage of fruits with one or more spots of scab(Venturia inaequalis). Dosage Average untreated 83.9 a 50 % 29.0 b 75% 21.0 c 100 % 13.4d Values in a column followed by the same letter(s) do not differ significantly From table 77 it can be seen that, as expected, the attack of scab increased as the dosage applied decreased. The spray volume had no effect on the efficacy of the treatment in this experiment (Table 78). Table 78. The average attack of scab on fruits. Spray volume Average 200 l/ha 22.8 a 100 l/ha 19.8 a Values in a column followed by the same letter(s) do not differ significantly There were differences in the susceptibility to scab between the different cultivars. Golden Delicious was the most susceptible and Cox's Orange Pippin the least susceptable cultivars. Table 79. The average attack of scab onfruits . Varieties Average Golden Delicious 37.7 a Jonagold 34.3 a Elstar 18.3b Schone van Boskoop 8.6 c Cox's Orange Pippin 6.7 c Values in a column followed by the same letter(s) do not differ significantly. Comparison of spraying devices A comparison was made between a cross-flow sprayer (Holder) and atunne l sprayer (Douven). The latter was equipped with Noric rotary atomizers. Trees were treated weekly with 50 and 100 % of the advised dosage of fungicides (e.g. 1.2 kg/ha captan was the standard rate of 100 %) for the control of scab (Venturia inaequalis). The cultivar was Jonagold and the trees were planted in a single row in 1986. There were four replicates. 107 The tunnel sprayer with rotary atomizers was less effective than the cross-flow sprayer (Table 80). As expected, the lower dosage was less effective than the higher dosage. Table 80. The average attack of scab on fruits. Treatment Average cross-flow 100 % 21.1 cross-flow 50 39.7 tunnel 100 51.4 tunnel 50 73.9 untreated 95.0 Values in a column followed by the same letter(s) do not differ significantly. Phytopathology and Weed Control Biology and control of secondary or sporadic disease in fruit crops H.A.Th, van der Scheer and J.J. Slabbekoorn Fireblight on apple and pear In 1994, the warning systems MARYBLYT and PAREFEU have been evaluated. MARY- BLYT has been operated in combination with a self-made computer program based on 'Billing Revised System' (BRS). The warning systems are applied in the blossom period of apple and pear. No warnings are given for the five trial fields in apple and the five in pear near Wilhelminadorp. Due to a somewhat higher temperature one warning was given for the trial field at Numansdorp. In 1994, none of the trial fields produced symptoms of fireblight, although in the previous year at least one out of every twenty trees was infected by the causal bacterium Erwinia amylovora. MARYBLYT, PAREFEU, and BRS differed significantly in the number of warnings given when the real temperature was enhanced by 3 °C or 6 °C. The same holds for the length of the incubation period calculated by the warning systems. The approximate results are given below. warning system number of warnings length of incubation period BRS moderate short to long MARYBLYT small long to very long PAREFEU many very short to short Due to rather low temperatures in the blossom period of apple and pear it could not be 108 determined which system best suits the situation inwhic h infections by Erwinia amylovora will occur. MARYBLYT is more user friendly than PAREFEU. MARYBLYT is easier to learn and more conveniently arranged. Input of data from local weather stations placed in orchards is an option for centrally operating a warning system in a fruit growing region. In so doing, it turned out that the temperature data from 9 METY-stations located in the province of Zeeland differed significantly. This hampers a regional-based warning service. Phytophthora rot in apple Attack on apple fruits by Phytophthora spp mainly occurs in the last three weeks before picking. At the regional experimental orchard in Numansdorp two sprays with 0.2% Luxan TMTD 80% spp at one and two weeks respectively before picking controlled the rotting in Elstar. Three sprays with 0.06 % Luxan Captan 83 %sp p at weekly intervals up to one week before picking were less effective. The same holds for one spray with Aliette one week before picking. Flower bud necrosis on pear Flower bud necrosis especially occurs in pear trees which do not have abalance d growth. Flower buds on the "unbalanced" pear trees are more susceptible to infection by Pseu domonas syringae. Necrotized buds are more prevalent intree s younger than ten years old and on trees that continue to grow in autumn. Conference is susceptible to this injury. In 1990/1991 in the Regional Experimental Orchard at Geldermalsen four sprays with an antibiotic reduced the incidence on Conference by half. The two sprays applied in spring brought about the main part of the reduction. Spraying with Luxan koperoxychloride spp (at the rate of 0.3% in the autumn, and 0.2% in the spring) was much less effective. In 1993/1994, again sprays with Luxan koperoxychloride spp, Aliette, Dimanin and two antibiotics were appliedo nConferenc e inautumn/winte r (once per month) andsprin g (once per week). The experiment was carried out at the Regional Experimental Orchards at Numansdorp and Zeewolde. However, none of the treatments reduced the incidence of flower bud necrosis. The incidence amounted to some 30% inth etria l field at Numansdorp and to some 50% in the trial field at Zeewolde. Early in the autumn of 1993, before the first spray was applied, necrosis of a small number of flower buds was observed at Zeewolde. Root rot in pear Inth e summer of 1992, anumbe r of pear growers was alarmed byth e death of young pear trees caused by the root rot fungus Roesleria pallida. In 1993/1994, a survey carried out in 23 fruit tree nurseries indicated the presence of apothecia of the pathogen on quince roots in older stool beds in half the number of plantings surveyed.Th e proportion of young stool beds of quince, planted spring 1993, with apothecia on the roots was even higher. In 1994, samples of dead and dying roots were taken from poorly growing pear trees in nurseries and orchards. The investigation was carried out in co-operation with Dr. K. Véghélyi from Budapest (Hungary), who spent some months at Wilhelminadorp at the invitation of the Research Station. In total 106 root samples were taken from 18 different 109 nurseries/orchards. The roots were enveloped in wet paper and kept in the dark at about 18 °C. Under these conditions fungal growth on the surface of the roots can be observed after a time. After two month in the dark, apothecia of R.pallida could be observed on circa one fifth of the number of root samples. However, more often growth of the root pathogen Rosellinia necatrix was observed on the roots. So far, this pathogen has hardly been observed in orchards and fruit tree nurseries in the Netherlands. In one case fruiting bodies of Xylaria polymorpha were observed on the crown of a poorly growing pear tree that suffered from wood rot. In vitro, Topsin M spp and Sportak were the most effective in controlling the growth of /?. pallida. However, treatment of slightly diseased pear trees with these fungicides did not improve their growth in 1994. Visibly healthy looking trees selected out of the same nursery grew better than the diseased ones. Testing of insecticides, fungicides and bactericides infrui t growing H.A.Th, van der Scheer Residual activity of fungicides In practice it is recommended to apply the DMI fungicides be applied for control of apple scab, caused by Venturia inaequalis, no longer than four days post-infection. For some years already, inth e Experimental Orchard at Geldermalsen good control of apple scab had been achieved by applying DMI fungicides six days post-infection. However, in 1994, seven days post-infection application of 0.08 % Baycor (+ 0.1 % Luxan Captan 83 % spp), 0.02% Dorado (+0.1 % Luxan captan 83 %) or 0.02 % BAS490F on Vista Bella apple trees gave no adequate control of scab. In the same trial regular application of 0.02 % BAS490F with an interval of two weeks between the spray applications gave fairly good control of scab. The effect on leaf scab was somewhat better than that on fruit scab. However, expanding the interval to three weeks resulted in inadequate control. Post-infection activity of fungicides In the Experimental Orchard at Geldermalsen post-infection spray schemes were applied to test some fungicides for controlling apple scab. The sprays were applied upt o four days post infection on older Golden Delicious trees. Luxan Captan 83 % spp was added to the DMI fungicides to achieve a preventive residual activity of seven days. Out of the three DMI fungicides Score, at a rate of 0.0375 %, gave slightly better control of apple scab than 0.08 % Baycor and 0.015 % Tridal. Spraying with 0.02 % BAS490F and 0.1 % SchAA 10780 adequately controlled the scab also. DMI resistance in Venturia inaequalis In 1994, many orchards were severely affected by scab.Contro l insprin g was difficult due to many showers of rain. Germination tests with V.inaequalis conidia originating from 28 orchards, revealed a reduced sensitivity towards Baycor. On average, the percentage of 110 conidia germinating in 25 mg/l Baycor was reduced only by half compared to germinating in water. Some spores even germinated in Baycor suspensions rated equal to half of the dosage recommended in practice. That applies also for conidia germinating in seven other DMI fungicide suspensions. In particular, conidia from two unsprayed orchards also showed a reduced sensitivity. Captan less effective? In the Experimental Orchard at Geldermalsen pre-blossom spray schemes with Luxan Captan 83 % spp at low dosages (0.075 % and 0.1 %) resulted in far too much scab on Golden Delicious and Vista Bella. Pre-blossom spray schemes with DelanFlowabl e at alo w dosage (0.025 % and 0.042 %) were more efficient. Presumably, the Captan was applied at too low a dosage under the very wet conditions of 1994 and it may be that Delan Flowable is more suitable in wet conditions than Captan. Fruit colour According to trial data from Belgium, treatments with Captan result in a more yellow background colour of Jonagold fruits, whereas treatments with fungicides containing manganese result in a more green background colour. Trials in 1993, carried out on Jonagold and Elstar did not support this data (see Annual Report 1993, p. 117). Directly after picking as well as after a period of cold storage, no significant differences in the background colour of the fruits were observed. Also in 1994, treatments with Captan or containing manganese fungicides on Jonagold did not affect the background colour of the fruits in the Regional Experimental Orchard at Horst. Supervised control of scab H.A. Th. van der Scheer Ascospore flights At Wilhelminadorp the first ripe ascospores of Venturia inaequalis were detected on 7 February. It took until 17 March before the first ascospores were trapped on glass slides fixed above overwintering apple leaves in the Regional Experimental Orchard at Numansdorp. At that time trees of, among others, the apple cultivar Belle de Boskoop just developed susceptible leaf tissue. On 9 June, ascospores were trapped for the last time that season. The progress of ascospore production was cultivar-dependant. The pseudothecia in leaves of the apple cultivar Vista Bella matured faster and therefore produced earlier ascospores in a large number than those in leaves of Elstar and Jonagold. Scab infections During each infection period up to mid-May 1994, a potted tree of the cultivar Vista Bella inth e Regional Experimental Orchard at Geldermalsen was exposed to scab attack. During that infection period the potted tree stood in the middle of a collection of overwintered leaves of the cultivars Elstar, Jonagold and Vista Bella. Before and afterwards the trees 111 were sheltered from rain. Scab occurred on each tree, even when trees were exposed to a light Mills infection period. Over Easter, at the beginning of April, much scab infection occurred on the trees exposed at that time. In the same period many ascospores were trapped on glass slides fixed above Vista Bella leaves inth e Regional Experimental Orchard at Numansdorp. The infection period of 6 May was in fact an extension of the one of 5 May. The length of the dry period in between justwas not quite eight hours. Considering the amount of scab that occurred on the tree exposed to infection on 6 May, a significant number of ascospores must have beendischarge d that day, or there must have been quite a number of ascospores in the air all the time since 5 May. In an orchard, the importance of an infection period in terms of scab attack can be demonstrated by leaving trees from untreated, and treating others with a post-infection active fungicide. That was done onVist a Bellatree s at Geldermalsen. Inparticula r omitting treatments in April resulted in many scabbed leaves on short shoots. The importance of an infection period can also be expressed as a value of the relative infection measure: RIM-value (see Annual Report 1993, p. 118). As in the previous year treatment with Score after each important infection period resulted in fairly good control of scab on Vista Bella at Geldermalsen. The fungicide was applied five times during the period of ascospore flights. Post-infection application of Score according to Mills Tabel, (also five treatments in total), resulted in an even slightly better control. Presumably due to the high inoculum pressure, no infection period could be ruled out as unimportant. The same trial was carried out at the Regional Experimental Orchard at Numansdorp. Unfortunately however, in that trial field hardly any attack occurred even in the untreated plots, despite the distribution in spring of overwintered scabbed leaves from another orchard. It may betha t the leaves were dried out too much during winter when they were kept in nylon mesh bags hanging above the orchard floor. Accelerating leaf drop Particularly on fertile soils, shoots of Elstar and Jonagold continue to grow rather long in the season. In that situation infective leaves are still present during and after picking time when fungicide application is no longer customary. Scab attack on these leaves results in a high inoculum pressure in the next year. To prevent that situation, 0.1 % Ethrel A and/or 2 % calcium chelate were applied mid-October on Elstar and Jonagold in an orchard at's- Heer Arendskerke to stimulate early leaf drop. One application with either one of these chemicals was sufficient to accelerate the leaf drop. A second treatment fourteen days later, combining both chemicals, or doubling the dosageo f both chemicals did not improve the result. Effect of planting system At the end of July the scab incidence on Jonagold was assessed in a trial field with different planting systems. The trees were planted three years earlier and showed many scabbed leaves in 1994. In the one-row-system and in the V-system circa 50 % of the shoots had scabbed leaves. That percentage amounted to 75 % in atwo-ro w system. In the one-row system both sides of each row had the same disease incidence. In the V- system the percentage of shoots with scabbed leaves inth e part of the trees insideth e "V" was circa 20 % higher than in the part of the trees outside. The same situation held for the 112 disease incidence of the shoots on the tree part "inside" and "outside" of the two-row- system. In this case the difference in disease incidence amounted to 15 %. Biological control of diseases in fruit crops H.A. Th. van der Scheer and E.I.L. Karelse In 1994, research on biological control of canker and scab on apple was directed to (stimulation of) micro-organisms with antagonistic properties. Also some attention was givent o biological control of fruit rot inappl e (seeprojec t "Fungicide use reduction in spray scheme for controlling storage rot"), and fruit and root rot in strawberry. Fruit rot in strawberry is mainly caused by Botrytis cinerea. Antagonists which can reduce the sporulation of B.cinerea on necrotic plant tissue, are available inth e Research Institute of Plant Protection (IPO-DLO) at Wageningen. It is planned to use them in strawberry cultures in the open. In this culture Botrytis fruit rot is much more a problem than in cultures sheltered under glass or in plastic tunnels. Instrawberr y growing onclosed-loo p fertigation systems,roo t rot caused by Phytophthora fragariae is athreat . At the Regional Experimental Station at Breda atria l was started to test a sand filter-bed to prevent the spreading of zoospores of P. fragariae. Canker on apple Inth e leaf drop period of 1993 trees of the cultivar Cox's Orange Pippin were sprayed two or more times - up to once per week - with suspensions of micro-organisms to prevent infection of leaf scars by Nectria galligena (see Annual Report 1993, p. 119). However, none of the treatments with a micro-organism reduced the infection of the leaf scars by the pathogen. Only the standard treatment - spraying twice with 0.1 % Topsin M at 10 % and 90 % leaf drop - gave 70 % reduction in the disease incidence. In another trial the antagonists were tested as wound dressings. In the autumn of 1993, the surface of the cankers inth e Cox's Orange Pippin appletree s was scarified with a knife and then painted with asuspensio n of an antagonist. However, inth e spring of 1994 only a few cankers started regrowth. Therefore good assessment of the effectiveness of the treatments could not be made. Nevertheless it became clear that the micro-organisms did not completely prohibit the growth of Nectria galligena. The same holds when scarified wounds are painted with Topsin-M pasta (standard treatment) or with the products Bio- baumanstrich and Tree seal, or when spraying the wounds with Scomrid aerosol. This project was alsomade possible with fundsfrom Eurofru Scab on apple In the autumn of 1993 a field trial was started to test the feasibility of a 5 % urea spray on scabbed leaves on the floor of the Regional Experimental Orchard at Zeewolde. The fallen leaves were first brushed to the grass strips, shredded and then sprayed with the urea. This treatment is an alternative for spraying the leaves with 5 %ure ajus t before they drop and requires one third less spray liquid and thus less urea per orchard. 113 However, in May 1994 disease incidence on leaves onshor t shoots of trees of the cultivars Elstar, Jonagold, and Belle de Boskoop was rather low and no significant differences between the treatments could be observed. Entomology and Biological Control Integrated control of pests on top fruits J. Woets Since 1945 the summer fruit tortrix Adoxophyes orana has been the dominant caterpillar pest in apple and pear in the Netherlands. For some years there have been indications that other leafroller species may play a part in the total leafroller damage estimated at harvest. There has been a low presence of summer fruit tortrix caterpillars, despite the usual damage levels, and a high moth catch of the other leafrollers in pheromone traps. These other potential leafroller pests are the dark fruit tree tortrix Pandemis heparana, the fruit tree tortrix Archips podana and the bud moth Spilonota ocellana. The caterpillars of the four above-mentioned species damage the fruits in an almost identical way. So it is difficult to establish a clear relationship between the number of caterpillars (in spring and autumn) or moths (in traps) of a certain species in the orchard and the damage occurring during harvest. Ideal experimental situations would be found in orchards where only one of the four species occurred. The relationship between numbers of caterpillars or moths and the damage level could be estimated per species and probably damage thresholds could be determined. Damage thresholds could be an important basis for decisions on (chemical) control, leading to careful and economic use, and also protecting the environment and avoiding resistance problems. Pest control advisers have been using damage thresholds for the codling moth Cydia pomonella for about the past eight years. Several situations occur annually in commercial orchards which do not fit into the actual knowledge onthreshold s and damage levels. New data could be helpful to etablish a more precise damage threshold for apples. During 1994 data were collected from the same 12 Jonagold plots of 1 ha as were used in the previous year. Caterpillars were counted in the trusses of flowers and on the leaves after harvest. Males were counted weekly in two sex pheromone traps per plot and the numbers of fruits damaged by leafrollers and codling moth were determined at harvest. In 8 out of the 12 plots no chemicals were applied for control of leafrollers and codling moth. The sampling of caterpillars in spring and autumn demonstrated very low numbers and did not indicate any relation with numbers of trapped moths or damaged fruits. The data on moth catches and damaged fruits in 1994 are presented in Table81 . As in 1993 there was a great variation in the numbers caught per species in the different orchards, and also with numbers of fruits eaten away. Putting together the data from the 12 plots in 1993 and 1994 a slight relationship came forward between the numbers of moths caught and numbers of damaged fruits for Adoxophyes orana andPandemis heparana, but afe w cases out of the 24 with significant damage play adominan t rôle. No relationship was apparent by the figures tor Adoxophyes orana and Spilnota ocellana. 114 Table 81. Average moth catches (with s.d.) of leafroller s and codling moth in two pheromone traps per plot and average numbers of damaged fruits, alsoa s a percentage, in the 12 1994-plots of Jonagold Moths of Catches Damage nr. % Adoxophyes orana 48 +/-81 Pandemis heparana 36 +/- 26 Archips polana 103 +/-97 33.5 1.67 Spilonota ocellana 83 +/-47 Cyd/'apomonella 59 +/-81 9.8 0.49 Apple casebearer In 1993 we found damage on 4.5 % of apple fruits by the apple casebearer Coleophora spinel/aan dth e alder casebearer Coleophoraserrate/la. Their presence hadbee n known for several years, but symptoms were seen only on the leaves before 1993. In 1994 the grower applied azinfos-methyl against the pest before pink stage. Following this no damage could be found on the crop. This was also the case in his other orchard some km away. We carried out some observations in the adjacent orchard in 1994. That grower had also seen casebearers on apple leaves for some years, but did not see damage to the fruit. We could ascertain that all damage in the apple plot was caused by the apple casebearer Coleophora spine/la. At harvest time 0.2 % of the fruit had been slightly damaged by the young caterpillars shortly after bloom. Coleophora serrate/la could only be found on apple trees close to the alder belt. As a specialist in Coleophoridae Van der Wolf identified the species. He said that Coleophora spine/la is really bound to apple and Coleophora serrate/la to Betulaceae. Some cases can be blown with alder leaves by the wind onto the apple crop, but that does not mean that apple is a host plant of Coleophora seratella. Mullein bug During 1993 and 1994 a new type of symptom occurred on apple fruits in orchards in the south-eastern Netherlands. The damage amounting to alarg e percentage, occurred mainly on Golden Delicious, but also to a lesser extent on Jonagold. During 1994 it became clear that this so-called pit disease was caused by larvae of the mullein bug Campylomma verbasci. In Europethi s bug was known only as apredato r on spider mites andlea f aphids. Biology and control of rosy apple aphid C.M.E.de Gendt From literature and field research the ideal control date in spring was determined as the moment when the first aphids appear as adults. Then all aphids are really hatched and so control by the available chemicals will be effective, partly because of the absence of 115 leafcurls. The period from hatching to the last moults of the fundatrices takes about four weeks. Besides the well known crumpled small fruits and curled leaves three other important aspects of damage were determined: 1. no new flower buds are formed on branches with many colonies 2. the growth of infested branches continues during autumn (no top bud formation) 3. if buds grow on infested branches, they may burst during autumn. Biological control of pests on strawberry and soft fruits J. Woets Garnation leafroller It so happened that the presence of the Mediterranean carnation leafroller Cacoecimorpha pronubana was dicovered inth e residential area of Kapelle (south-western Netherlands) in 1993. In co-operation with the Plant Protection Service a survey was carried out on the distribution of this exotic species. This pest presents a big threat to Dutch crops both outdoors and in greenhouses. A pheromone trap was used to determine the distribution. It consisted of adeltatyp e trap withth eBASF-dispense r RAK-4.Thi sdispense r contains 250mg .z-1 1-tetradeceny/acetat e and is meant to be used for pheromone disruption of green leafrollers into p fruit orchards. The traps were placed at a height of 1.50-2.00 m in different habitats such as gardens, parks, small fruit gardens, apple orchards and in and near carnation greenhouses. They were distributed in and around the twin villages of Kapelle and Biezelinge, along a co ordinated system in that province of Zeeland, and in 10 orchards in other parts of the Netherlands. The trapping period lasted from May-October 1994. When 80-300 males were caught in a trap, the caterpillars could be found within a distance of 30 m. Where 25-50 males were trapped, the distance to the nearest source (host plants with caterpillars) was 100 m maximum. Catches of 3-16 specimens per trap indicated a source at a distance of at least 1 km. So the presence of caterpillars was determined in three towns in the south-western Dutch province of Zeeland. Probably caterpillars were also present in two other places with low catches (< 10 per trap). Caterpillars were found on raspberry and some of the usual species of shrub found in gardens and parks such as the evergreen Lonicera nit/da cv. Elegantissima and the deciduous shrubs Ligustrum ovalifolium, Philadelplus and Symphoricarpus albus. In mid- February 1995 caterpillars were found eating on the evergreen Lonicera nitida. The maximum numbers O300 per trap) were caught at a spot where carnations grown in greenhouses until 1983, when the greenhouses were removed. So the occurrence outdoors had been there since at least 1983. Winter temperatures in 1984-1985 were as low as -14°C. At present the distribution area is only about 1 km long, probably because the females are not at all inclined to dispersion. The biggest risk of a wider spread is the distribution of plants by nurseries. 116 Integrated fruit growing A.M.E. Schenk, C. Dekker, H. Veijer Farming systems research Materials and methods The aim of the Integrated Fruit Growing project is to develop an economic production of apple, minimizing the undesirable side effects for human health and the environment. The experiment was located in two experimental gardens, Numansdorp and Zeewolde. At each location, a comparison was made between three systems of fruit growing (3 trials): current, integrated and minimum. In spring 1990, eight apple cultivars were planted in single rows (3 x 1.25m) with each cultivar in two to four rows. The apple cultivars were widley grown - Elstar, Jonagold, Alkmene, Cox's, Discovery, Rode Boskoop - and the scab and mildew resistant hybrids from the CPRO (Ecolette and 78039-27). Each trial comprised 0.5 ha. In trial 1, all treatments and techniques used, were approved in accordance with the guidelines for Integrated Fruit Growing. Predatory mites were introduced and selective pesticides were used. Decision making schemes for disease control were followed. In trial 2, lower dosages of pesticides were used. Only products allowed in ground water protection areas were sprayed. Herbicide use was decreased by reducing the weed free strip. Products used as insecticides were safe for predatory mites and also for other predators. Decision making schemes for disease control were followed. In trial 3, a minimal use of pesticides was tried replacing them by biological and mechanical techniques. Decision making schemes for disease control were followed as well. Results Mites (Typhlodromus pyri.Acutus schlechtendali, Panonychus ulmi) A biological balance has been established with the following characteristics: no spider mites, few rust mites and few predatory mites. Numansdorp Zeewolde Trial 1 Trial 1 rustmite seiöer mite • rustmite — — - precj m,te spider mite 5/»l 6>91 Tlf Figure 13. Mite population in trial 1 in Numansdorp and Zeewolde 117 Numansdorp Zeewolde Trial 2 Trial 2 rustmite spider mite rustmite pred. mite spider mite 400 1 • 300 | 300 200 - ! | 200 10O i I--V....1—»••" i i i Xi...""i i V'L.VJi 3*1 0/91 7/91 6/92 7/93 6/92 9/92 6/93 7/93 0/93 9/9310/930/»* 7/04 6/94 9*4 10*» 7/93 6*3 9*3 6*4 7*4 0*4 Figure 14. Mite population in trial 2 in Numansdorp and Zeewolde Numansdorp Zeewolde Trial 3 pider mite rustmite pred. mite Trial 3 • spider mite rustmite pred. mite 300 200 100 —i—k' w..j.. / i \ ..,^-d—i i I-" i i i _ 9*1 6*1 7*1 0*2 7*2 0*a 9*2 0*3 7*3 0*3 9*3 10*30*4 7*4 6*4 9*4 10*4 Figure 15. Mite population in trial 3 in Numansdorp and Zeewolde Rosyapple aphid (Disaphis plantaginea) Table 82. Infestation of rosy apple aphid in June and damage at harvest 1994. Infestation in June in % Damage at harvest in of the kg-production NU ZE NU ZE Trial 1 1 4 0.0 0.1 Trial 2 3 2 0.0 0.2 Trial 3 2 10 0.1 0.2 118 In Numansdorp and Zeewolde rosy apple aphid was found, but it was not really a problem. In each of trials 1 and 2, a control treatment was carried out twice each with 30 g Pirimor. Trial 3 was treated once with 20 g Pirimor. In June, rosy apple aphid could still be found (Table 82). Damage at harvest was recorded as well and is expressed in Table 82 as percentage of the kg of fruits harvested. Leafrollers (Tortricidae) Codling moth has not been controlled in trial 1 because the threshold level was not reached (Table 83). The amount of pheromone dispensers was reduced in 1992 from 500 to 300 because damage was very low in 1991 (0.1 to 0.6 %). From detailed studies it was concluded that 300 dispensers per ha was too low. In some cases control was not satisfactory. Therefore since 1992, 500 dispensers par ha are being used. Table 83. Treatment and damage of codling moth (Cm) and leafrollers (Lr) in 1994 Treatment Damage at harvest in % of the kg-prod. ZE NU ZE NU Lr Cm Lr Cm Trial 1 0.3 0.0 0.6 0.0 Trial 2 Pher. Pher. 0.3 0.0 0.4 0.0 Trial 3 Pher. Pher. 0.7 0.0 0.2 0.0 Orthosia sp., Erannis defoliaria,Operophtera brumata The threshold level of two caterpillars per 100 clusters was not reached in 1994 (Table B4), so no control measures were carried out. The damage caused by Orthosia is given n Table 84. Table 84. Treatment and damage by Orthosia sp. in 1994 Treatment Damage at harvest in % of the kg-prod. ZE NU ZE NU Trial 1 0.8 0.6 Trial 2 - 1.3 0.4 Trial 3 1.7 1.4 Earwig (Forficula auricularia) While controlling the sacks of earwigs it became clear that the distribution of earwigs was very variable throughout the area. In some trees, one hundred earwigs could be found, and in other trees nearby only a very few. This could be explained by their im ite d horizontal migration. In 1994, the peak of the earwig population was reached in July (Fig. 16) The very high peak of earwigs in Zeewolde in June 1992 is remarkable. At that time there was a high attack of aphids, but not so high that atreatmen t was needed. It is known that earwigs live very near to their food. 119 EARWIG POPULATION Numansdorp 50 07/m owoi ow»i ocyoz own mm ot/u own arm own oe/w os/w OWM 07/M WM Time CPRO-27 CPHO-18 Boskoop Discovery Cox's Alkmene Jonagold Elstar EARWIG POPULATION Zeewolde î •a o c 3 O CPRO-27 CPRO-18 Boskoop Discovery Cox's Alkmene Jonagold Elstar Figure 16. Development of earwig population in Numansdorp and Zeewolde fron 1991 until 1994. 120 Common green capsid(Lygus pabulinus) Common green capsid was found and controlled in Numansdorp with Undeen in trials 1 and 2. In the latter trial Undeen was also used, because no good alternative is available. However, in trial 2, Undeen was only used once and only after the insect was obser ved. In trial 3 no control treatment was made. Damage in Numansdorp was maximal 0.2 %, and in Zeewolde 0.5 %. Scab(Venturia inaequalis) andpowdery mildew (Podosphaera leucotricha) Scab was controlle by a preventive captan treatment combined with the curative Dorado in case of severe infection. Mildew was controlled in trials 1 and 2 with Pallitop. In trial 3, shoots attacked by powdery mildew were eliminated by hand. Jonagold had most scab, the percentage of infected shoots in August was high but, because of low infection in spring damage at harvest was not very high (Table 85). Table 85. Percentage scab-infected long shoots in August 1994 and percentage scab-infected kg at harvest 1994 for Jonagold. Shoots Production NU ZE NU ZE Trial 1 78 33 1.3 4.3 Trial 2 54 45 2.3 6.6 Trial 3 53 45 1.8 5.2 In 1994, there was not the remarkable difference between susceptibility of the cultivars as in previous years (Table 86). No scab control was carried out on the CPRO selecti ons CPRO-78039-27 and Ecolette, since these are scab resistant. Table 86. Differences n scab susceptibility of cultivars. Percentage scab infected kg at harvest in 1994. Cultivar Trial 1 Trial 2 Trial 3 NU ZE NU ZE NU ZE Elstar 1.7 3.4 1.7 4.7 1.2 5.9 Jonagold 4.1 - 2.6 - 2.6 - Alkmene 0.8 3.7 3.0 4.8 2.2 5.5 Cox's O.P. 2.5 9.0 2.8 1.5 2.3 8.1 Discovery 1.6 3.6 4.6 6.1 3.1 5.0 Rode Boskoop 2.0 8.7 5.0 16.3 0.0 0.0 Ecolette 0.0 0.0 0.0 0.0 0.0 0.0 CPRO-78039-27 0.0 0.0 0.0 0.0 0.2 0.0 121 Fruittree canker (Nectria galligena) Captan treatments were carried out against fruit tree canker in trials 1 and 2. In trial 3, canker wounds were cut out. In winter 1994-1995 damage was recorded (Table 87). Table 87. Treatment and damage of fruit tree canker in 1994 Treatment against canker Number of canker wounds per trial in 1994 NU ZE Trial 1: 2 x 187 g Captan 67 28 Trial 2: 2 x 125 g Captan 48 48 Trial 3: manual wound treatment 168 76 Weed control Trial 1 : All methods and products used are in agreement with the guidelines foi Integrated Fruit Production. These products were satisfactory. Trial 2: Max. 2 litres Roundup, 1 litre MCPA, 1 litre Finale were used per ha. A reduction of herbicide use was achieved here by having a smaller weed- free strip. Trial 3: Max. 1 litre Roundup per ha was used in Zeewolde to keep a small strip weed-free and in Numansdorp to control weeds at the borders of the polypropylene cloth that covered the soil. Useof growth regulators The choice for the type of growth regulation in the three trials was based on the following considerations: in trial 1 all legal growth regulators could be used, if necessa ry. In trial 2, carbaryl was omitted because it kills natural enemies being a broad spectrum insecticide. In trial 3, only GA4+7 was used and thinning was done by hand. Table 88. Use of growth regulators (in g a.i./ha) in Numansdorp en Zeewolde ir 1994 Trial 1 Trial 2 Trial 3 GA4+7 10 10 10 (all cultivars 2 x) Carbaryl 63 0 0 (Alkmene 100g) Amid-thin 55 55 0 (All cultivars except Alkmene) Total 128 65 10 122 Table 89. Use of pesticides (in kg a.i./ha) in 1994 in Numansdorp and Zeewolde Trial 1 Trial 2 Trial 3 NUMANSDORP fungicides Captan 36,7 33,6 26,9 Dorado 0,4 0,4 0,4 Pallitop 0,5 0,4 Total fungicides 37,6 34,4 27,3 insecticides Pirimor 0,3 0,2 0,1 Undeen 0,5 0,5 Total insecticides 3,6 1,3 0,1 herbicides Roundup 0,9 0,4 0,8 MCPA 0,5 0,8 Diuron 0,4 Simazin 0,6 Amitrol 1,2 Finale 0,1 Total herbicides 3,6 1,3 0,8 Total pesticides 42,0 36,4 28,2 ZEEWOLDE fungicides Captan 30,1 28,5 24,6 Dorado 0,2 0,2 0,2 Pallitop 0,6 0,4 Total fungicides 30,9 29,1 24,8 insecticides Pirimor 0,4 0,3 0,1 Undeen 0,6 Total insecticides 1,0 0,3 0,1 herbicides Roundup 0,7 0,3 MCPA 0,5 Diuron 0,5 Butisan S 0,5 Total herbicides 1,7 0,5 0,3 Totaal pesticides 33,6 29,9 25,2 123 Useof pesticides Eighty percent of the pesticides used were fungicides, mostly for scab control. Scat control was the same for the three trials and therefore the differences between tht three trials were only slight (Table 89). Table 90. Environmental score per trial in 1994 Product Total score per product per trial Numansdorp Zeewolde water soil groundw. water soil groundw. trial 1 Amitrol 15 0 0 _ _ _ Butisan S - - - 3 0 1 Diuron 2 2 120 3 3 150 MCPA 0 0 50 - - - Roundup 8 0 0 6 0 0 Simazin 5 2 2000 - - - Captan 17238 442 44 14157 363 36 Dorado 4 1 1 2 1 0 Pallitop 12 0 0 14 0 0 Pirimor 198 468 1 264 624 2 Undeen 540 270 15000 648 324 18000 total 18022 1185 17215 15097 1315 18189 trial 2 Finale 0 0 10 _ _ - MCPA 0 0 75 0 0 50 Roundup 3 0 0 - - - Captan 15776 405 40 13416 344 34 Dorado 4 1 0 2 1 0 Pallitop 9 0 0 10 0 0 Pirimor 132 312 1 165 390 1 Undeen 540 270 15000 - - - total 16464 988 15126 13593 735 85 trial 3 Roundup 4 0 0 2 0 0 Captan 12636 324 32 11544 296 30 Dorado 4 1 0 2 1 0 Pirimor 66 156 1 83 195 1 total 12710 481 33 11631 492 31 124 Use of theenvironmental yardstick i/Vhen choosing pesticides and growth regulators the environmental yardstick for Desticides was used, described in detail elsewhere (Reus, 1993). This yardstick makes t possible to compare the effects of different pesticides on soil organisms, water Drganisms and leaching to ground water. In 1994 it again became clear that the choices n integrated pest management are limited. However, it is possible to achieve a great improvements by choosing the right pestici des. A great reduction in fungicide use could be achieved by using curative fungicides but because of the danger of resistance of scab this is not a good strategy. Within the nsecticides Undeen is the most polluting product. Last year Nexion was used in trial 2 but this product is no longer approved so we had to use Undeen also in trial 2 but only after observation of common green capsid Table 90 gives the scores for all products jsed. Fertilization Before planting in trial 3, 80 and 40 tons stable dung per ha were used in Numansdorp and Zeewolde respectively. In 1991, based on soil analyses it was decided only to fertigate in Zeewolde under dry conditions and in Numansdorp to add only 7,5 g nitrogen per tree. In 1992 19 g nitrogen per tree was fertigated based on leaf analyses. In Zeewolde no fertigation was given. In 1993 in Numansdorp in all 3 trials 30 g nitrogen was fertigated, based on leaf analyses. In trials 1 and 2, 20 g potassium and 16 g magnesium were given. In Zeewolde no fertigation was given. In 1994 based on leaf analyses fertigation was given in Numansdorp and Zeewolde. In Zeewolde in all three trials 40 g nitrogen, 13 g phosphorus and 44 g potassium were given; in Numans dorp 19 g nitrogen was given in all 3 trials, 20 g phosphorus and 10 g magnesium were given in the standard and integrated trial and 12 g phosphorus was given in the minimum trial. Production in 1994 In 1994 in Zeewolde, trial 2 and 3 yielded more than trial 1, but in Numansdorp trial 1 gave the highest production (table 91). The accumulated production in Zeewolde is still Table 91. Production in 1994 Zeewolde Numansdorp Tr.1 Tr.2 Tr.3 Tr.1 Tr.2 Tr.3 Production in tons/ha in 1994 54 58 58 54 48 48 Production in tons/ha in 1991-1994 170 175 158 126 116 128 Fruit damage by insects in % prod. 1.6 2.3 4.0 2.4 2.8 2.5 Fruit damage by scab in % prod. 5.2 7.7 6.3 1.3 2.3 1.8 125 somewhat lower for trial 3, but the difference with the other two plots is diminishing. In Numansdorp, trial 3 had the highest accumulated production although the difference with trial 1 was very small. The percentage of fruit damaged by either insects or scab is also given in Table 91. Labour All labour except observation time was recorded during 1994. In Numansdorp mos1 labour was required in trial 3. By omitting chemical thinning and canker control a lot ol work had to be done by hand. Compared with trials 1 and 2, 30 % more time was needed for cutting out canker wounds (two hours) and 25 extra hours were needed for hand thinning. In Zeewolde the differences were smaller. For trial 3, less labour was required for weed control but more for canker control and mowing. For picking 135 kg/h and for grading 100 kg/h were estimated (Table 92). Table 92. Labour requirement (man-hours/ha) in 1994 Trial 1 Trial 2 Trial 3 Numansdorp 1196 1077 1159 excl. picking and sorting 256 241 323 Zeewolde 1233 1303 1311 excl. picking and sorting 276 293 301 Economicalevaluation An economic evaluation has been undertaken to examine the economics of the three trials. These results are reported on page 80 - 82. References Reus, I.A.W.A., 1993. An environmental yardstick for pesticides: An instrument to measure the environmental impact of pesticides. Acta Horticulturae 347: 215-224 126 List of chemicals Trade name Commonnam e Algadde Diamin 330 g/l alkyldimethylbenzylamonium- chloride Fungicides en Herbicides Aliette fosetyl aluminium 80 % Amitrol amitrol 25 % BAS490F strobilurine analogue 50 % Baycor Butisan S Delan Flowable 750 g/l dithianon Dimilin diflubenzuron 25 % Diuron diuron 80 % Dorado pyrifenox 25 % Finale gluphosinate-ammonium 20 % Insegar fenoxycarb 25 % Luxan captan captan 83 % Luxan koperoxychloride spp copperoxychloride 50 % Luxan TMTD 80 % spp MCPA MCPP mecoprop 60 % Nexion bromophos 24 % Pallitop nitrothal-isopropyl 50 % Pirimor pirimicarb 50 % Roundup glyphosate 36 % SchAA 10780 50 g/l fluquinconazol + 200 g/l pyrimetanil Score difeconazol 10 % Simazin simazin 50 % Sportak 450 g/l prochloraz Topsin M spp thiophanate-methyl 70 % Tridal 120 g/l nuarimol Undeen propoxur 50 % Insecticides Dimilin 25 % diflubenzuron Insegar 25 % fenoxycarb RAK 3 250 mg codlemone (E,E-8,10 dodeca- dienol) 127 RAK 4 250 mg Z-11- tetradecenylacetate RAK 9 250 mg Z-8-tetradecenylacetate Growth regulators Calcium chelate calcium chelate Ethrel A 480 g/l ethefon GA3 (Berelex) 9,6 % gibberellin A3 GA4+7 (Berelex A4/A7) 0,89 % gibberellin A4+7 + 0,06 % gib berellin A13 Promalin giberellin 19 g/l + benzyladenine 19 g/l CCC 457 g/l chlormequat Wound dressing Bio-baumansrich plant extract + kaolin Scomrid aerosol imazalil 2 % + azaconazol 1 % Topsin-M pasta thiophanate-methyl 3 % Tree seal bitumen emulsion 30 % + synthetic 128 List of Entries ^ctinidia Arguta (Siberian gooseberry)15 - De Jager K ^ctinidia kolomikta (Mandsjoerian goos- - De Jager Zw äberry) 15 - Elnica Mgacide - Flikweert Dimanin 109 - Flikweert K antagonists 113 - Heines (\pple - Huisman biological control 113 - Jacobs chimaeras 43 - Nodop clones - PFW-lla,-llb - Cox's Orange Pippin 41 - Rietveld II - Buysens - Roelofs - Crimson Cox - Van der Plasse - De Bruyn - Van der Zalm II - Flikweert - Van Kaam - Heidens - Van Kampen - In 't Veld - Van Liere I, II - Korallo - Van Wijk - Kummer B 396 - Vlaar - Queen Cox B 293 - Jonagold 43 - Queen Cox EML A - 2000 - Roelse -4001 - Steyn - Boerekamp -T 12 - Boonen -T 1088 - Braun - Van der Ploeg - Crowngold - Van der Rijdt - Daamen II - Van Vliet-2 - Dalijo - Van Vliet-4 - Decosta - Van Vliet M - Eversdijk I, II, III, IV - Vroemen - Fernelmont - Zwanenburg - Glerum -Elstar 43 - Groffils - Bel-El ( = Elswout) - Heines - Boerekamp - Jomured - Bosman - Jonabel - Bougie - Jonagored - Bruynzeel I, II, III - Jonagored 9614 - Daamen I, II - Jonagored HR 2458 - Daliest - Jonakap - Daliter - Jonaveld - De Bruin - Jorayca 129 - King Jonagold 8765T - Dayton - Ley - Delprivale - Lindenbergh - Discovery - Martens 1, II - Elstar - Meesters - Generös - New Jonagold R.N. - Gloria - Nijsten - Golden Delicious Rozendaal - Novajo - Graaf Ezzo - PFW-II -H1146 - Prince Jonagold d'Haemer -H1152 - Reniers 1, II -H1165 - Romagold -H1166 - Ruissen -H1171 - Schneica B -H1177 - Stassen -H1181 - Van Weverwijk -H1187 - Van der Bliek - H1195 - Verbruggen -H1200 - Verploeg -H1205 - Waterval -H1209 - Zweeren -H1210 - Queen Cox 42 -H1217 -Kloon 7, 9, 13, 14, 18, -H1237 56, 91, 106 - Hongaru - Heines 4 - Jonagold - cultivars 36 - Joseph Musch - 8C-5-62 - Karmijn de Sonnaville -8L-13-13 - Kogestu - 8M-2-8 -L36 - 8NE-7-72 -L41 -9P-15-30 -L45 - 11W-19-18 - Margol - A92/23 - Merlyn - A235/1 -NY617 - Baujade -NY619 - Beemstervroeg - NY678 - BM 46591 - Otava -BM 47671 - Pi.A.24.5 -BM 50717 - Pilot -BM 51880 - Pinova -BM 54859 - Pionier - Celica (Welbo) - Primica - Co-op 27 - Realke - Co-op 28 - Reandra - Co-op 29 - RedAroma - Co-op 31 - Reka - Cox's Orange Pippin - Relinda - CPRO 78038-9 - Renora -CPRO 78039-18 - Rewena 130 - Rode Boskoop SHKL - pollination 57 - Rode Boskoop H. v.d. Vliet - good seeds/fruit - Romus II - fruit set - Romus-3 - fruit colour - Rosana - rootstocks 11 - Rubinola -CG 65 - Schone van Boskoop - Pi-Au 7-33, 9-16, 51-11, 56-83 - Vanda - Rosy apple aphid 115 - Vegi Cox's O.P. - scab resistant 36 - Voinea - self fertile 42 - Williams Pride - shoot lenght 45 -X3177 - storage 88 - X 4876 - supervised control 111 diseases - susceptibility 57 - fireblight 108 - non-resistant cultivars 39 - storage diseases 92 - Alkmene - canker 137 - Cox's O.P. - mildew 39 - Discovery - Phytophthora-rot 109 - Elise - scab 37, 39, 111 - Elstar Dysaphis plantaginea (see Rosy apple - Gala (Royal Prince) aphid) - Golden Delicious eating quality 36 - Jonagold - cultivars - Rode Boskoop - Baujade - resistant cultivars 39 - Coop 29 - CPRO 78038-9 - CPRO 78038-9 - CPRO 84015-17 -CPRO 80015-47 - Ecolette (CPRO 78039-18) - Delblush - Enterprise (Coop 30) - Ecolette - Fiorina - Elstar - Merlijn - Enterprise - Otava - Golden Delicious - Prima - Jonagold - Priscilla - Margot - Rosana - Pinova - SA 15/4 - Reka - Vanda - Retina - temperature 84 - Rewena - trunk circumference 41 - SA 15/4 Avanced harvest fruit size 41 - blackberry (tunnel) 68 fruit development 84 - raspberry (tunnel) 66 - ground colour - strawberry (glasshouse) 59 - firmness Arrangement 20 - quality Bacterium 108 - ripening - Erwinia amylovora ground colour 20 - Pseudomas syringae growth regulators (see there) Black currant leaf drop 113 - cultivars 64 131 -Andega - chemical control 11C - Ben Alder - testing pesticide - Ben Connon - supervised control 111 - Ben Loyal - apple scab - Ben Tirran Boron 105 - Ben Tron CA-storage 8£ - Bo 576 - pear - Bona Chemical thinning u - Ceres (76/69) Cherry (seeals o sweet cherry) 5E - Climax Cultivars - E.C.M. - Actinidia spp. 12 - Eva - apple 3€ - Farleigh - black currant 61 - Favourite - blackberry 66 - Foxendown - gooseberry 6E - Haakon - hazelnut i: - Kartijciai - Japanese pear 16 - Ojebijn. - pear 46 - Polar - plum 5E - Sel. K.W. - quince 1E - Silmu - raspberry 6€ - Storklas - red currant 7C - Tifon - sour cherry 56 - Titania - strawberry 5£ - Triton - sweet cherry 56 - Troll - walnut 1E - Tsema Delayed harvest - Vakarial - raspberry (tunnel) 6e - Viola - strawberry 72 Blackberry 68 Diseases - cultivars - apple - 83465 - canker 111 - 83466 - fireblight 106 - Arapaho - Phytophthora fruit rot 106 - Bodermo -scab 37,39,11( - Chester Thornless - storage diseases 92 - Jam Fall Black - pear 106 - Jumbo - fireblight - Kotata - flower bud necrosis - Waldo - root rot Crop protection 108 - strawberry n: - biological control - fruit rot - apple 111 - root rot - canker Economics - scab - environment 8( - strawberry 113 - farm model - fruit rot - farm systeem - root rot - farm model 7< - sand filterbed - light 132 - environment - Golda - farm system 83 - Goudbal - integrated fruit production - Greenfinch - planting density 74 - Invicta - apple - May Duke - pear - Rosko - price 76 - Starfructa Dunkelrot - apple - Weisse Neckertal - tree - Whinham's Industry Feathering 17 Ground colour 20,84 Fertigation 100 - apple - boron Growth regulators Fertilization (see leaf fertilization, ferti- - chemical thinners 26 gation) - Atoclair Flowering date 6 - carbaryl Fruit colour 111 - D4017 - apple - Lex 9476 Fruit tree nursery 16 - NAAm (Amid Thin) Fungicide 110 - Neusodan - Aliette - leaf drop stimulator 112 - BAS 490 F - calcium chelate - Baycor - Ethrel A - Delan Flowable Hazelnut 13 - Dorado Integrated fruit production 117 - Luxan Captan 83% spp Integrated biological control 114 - Luxan koperchloride Japanese Pear (Pyrus pyrifolia) 16 - Luxan TMTD 80% spp - cultivars - manganese containing fungicides - Chojuro -SchAA 10780 - Kosui - Score - Hayatama - Sportak - Hosui - Topsin M spp - Niitaka - Tridal - Shinko Fungicide resistance 110 - Shinsui Fungus - Shinseiki - Botrytis cinerea 113 - Tama - Nectria galligena 113 - decoration material - Phytophthora fragariae 113 - fruit weight - Phytophthora spp. 109 - growth - Roesleria pallida 110 - iron deficiency- production - Roselina necatrix 109 - taste - Trichoderma sp. 113 - trunk circumference - Venturia inaequalis 110 Lateral shoots - Xy/aria polymorpha 110 - soil temperature 86 Gooseberry 65 Light 20 - cultivars Leaf fertilization 102 - Achilles - borium - Early Sulphur - manganese - EM-selecties (Pax) - sink 133 Mandsjoerian gooseberry 15 - P152/8 - cultivars - PB 30/6 Manganese 102 - Pierre Corneille Pear - Sierra - black skin 33 - St. Augustinus - cropping level - Suypeer - gibberellins - Verdi (CPRO 66006-273) - fruit analysis - Zaailing Van Liere - breaking force 13 - diseases - clones - fireblight - Conference 51 - flower bud necrosis - Brons - root rot - Goud - disorders - Saels 1 - black-skin - Saels II - firmness -T 1388 - fruit size/ weight - Doyenné du Cornice 54 - keepability (storage) -9-3 - leaf colour -9-6 - minerals - 18-21 - picking date - 10-28 - pollination - M.204 - fruit set -T 1388 - good seeds/fruit - cropping level 53 - production - cultivars 18 - Pseudomonas syringae -6.30.100 - red discoloration - Abate Fétel - red motte - Baurotard (Dairain®) - red skin - Beurré Hardy rood A - rootstocks - Beurré hardy rood C -BA29 - Concorde - Kwee MC - Conference -OH 11 - Conference Brons -OH 20 - Conference Vlaskamp -OH 33 - Conference Goud - OHxF 333 -CPRO 68006-123 - Quince MC - CPRO 69007-36 -QR 193-16 - Delbuena (Peradel®) - RV 139 - Delwilmor -S 1, S3 - Dolacomi (Jowil®) - russeting - Doyenné du Cornice - seeds/fruit - Gieser Wildeman - self pollination - Hartman -susceptibility to -I/9 - fireblight - K2 07-72 - scab - Lombacad (Cascade®) - taste test - Massoek - Clapp's Favourite - P46/5 - Conference - P83/13 - CPRO 69007-36 134 - Delete - fruit weight - Doyenné du Comice - picking date 74 - Delbuena - picking period 74 - Delmoip - production 74 - Dolacomi - taste 74 - Triomphe de Vienne Pollination/self pollination 57 - Verdi Quality - tree volume 54 - ground colour 84 Pests 116 Quince (Cydonia oblonga) 15 - Adoxophyes oran a - summerfruit tor- - cultivars trix - Agvambari - Archips podana - fruit tree tortrix - Bourgeault - Cacoecimorpha pronubana - carnation - Ekmek leafroller - 1/18 - Campylomma verbasci - mullein bug - I/25 - Coleophora seratella - case bearer on - Leskovacka Betulacea - Ludovic - Coleophora spinella - apple case bea- - Morava rer - Rea's Mammoth - Cydeapomonella - codling moth - Ronda - Dysaphis plantiginea - rosy apple - Shams aphid - Sobu - Pandemis heparana • dark fruit tree - Vranja tortrix - dry matter - Spilonota ocellana - bud moth - minerals Pink currant - CA-content - storage 90 - production Planting density 20 - vitamine C-content - apple Rainfall 6 - pear Raspberry Plantmaterial 16 - cultivars - interstem tree - autumn bearing cultivars 66 - one-year-old tree - Autumn Bliss - snip tree - Dinkum Plantsystem - Douglas - apple 20 - Favourite - pear 23 - Heritage Plum - Luilin Galante - cultivars 55 - Polana - Anna Späth - Princesse Rossana - Avalon - Ruby - Excalibur - summer bearing cultivars 66,67 - Jubileum - Algonquin - Madeleine - Beskid - Opal - Comox - Reine-Claude Souffriau - Elida - V72511 - Gaia - Valor - Glen Clova - Victoria - Glen Lyon 135 - Glen Moy - Mivana - Glen Prosen - Mulka - Gradina - Nortun - Granat - Präkanda - Himbo Queen - Prince Albert - Julia - Red Lake - Marwé - Redstart Redpoll - Meeker - Rode Rebel - Pechts Gigant - Rolan - Proma - Rondom J-selecties - Redsetter - Rondom J - Resa - Rondom H - Ru 74 - Rondom G5 - Rumiloba - Rondom Ra - Rutrago - Rondom Rb - Schönemann - Roodneus - Sei. Eversdijk - Rotet - Tulameen - Rovada - harvest 66 - Soeur de Claire - advanced - Stanza - delayed - Tatran Red currant 61 - Traubenwunder - advanced harvest 70 Root pruning - Jonkheer van Tets - apple 27 - Junifer - fruit firmness - containers 70 - pear 29 - cultivars 62 - growth control - 1967 Rootstocks - A32 - apple 11 - A105 - pear 9 - Augustus Scald 92 -B11 Siberian gooseberry - Cocagne - cultivars 15 - Cassa Soil temperature 86 - Detvan Spraying (see also leaf fertigation) 104 - EM 1503/35 = Redwing Taste testing - Fay's Prolific - pear 52 - Fertöd - apple 36 - Fortun Spraying technique 104 - Herosta Sprayings 104 - Hron Sprinkling 101 - Jodes Storage 88 - Jonkheer v. Tets - CA-storage - Jotun - carbon dioxyde - Junifer - cluster size - Laxton no.1 - colour - Laxton Perfection - quality - London Market - scald - Mactor - skin spots 136 - storage period - European cultivar trial 60 - temperature - in-vitro-material 72 - pear - light intensity 71 - Conference 96 - planting dates 71 - brown heart - planting density 71 - orchard factors - propagation 71 - Doyenné du Cornice - substrate 71 - internal disorders 88 - trayplants 72 - pink currant 90 - cold-stored - red currant 91 - flower initiation - ULO-storage 94 - gibberellin - white currant 91 - lifting date Storage diseases 96 - illumination - brown core - root rot - brown heart - fruit rot - colour Sweet cherry - quality measurements - cultivars 56 Storage techniques 88 - 13S-33-34 - frost damage - 13S-49-24 Strawberry - Cognac - closed growing systems 73 - Garnet - illumination - Gerema - cold units - Giorgia - cultivars - Hartland (NY3308) - cold stored waitingbed plants 60 - Karneol - Cortina - Kordia - CPRO-selecties - Lapins - Darline - Maru (Ruby®) - Gardena - Regina - Gerida - Schneiders Späte Knorpelkirsche - Sella - Summit - everbearers 60 - Somerset (NY6476) -CPRO 1036 - Sunburst - Calypso - Sweetheart - Evita - Sylvia - Mrak - Vista - Rapella - firmness - Sunset - picking period - glasshouse crop 59 - production - CPRO-selecties - rain cracking susceptibility 56 - Elsanta Temperature - Darline - air 6 - Karola - day/night 85 - Primella - soil 86 - June bearing cultivars 60 Trace elements 100 - CPRO-selecties - borium - Elsanta - manganese - Darline 91 - zinc - diseases 112 Transpiration 100 137 - global radiation - leaf area - light interception - reference transpiration - soil transpiration - stem heat balance method - temperature - transpiration factor - water vapour pressure deficit - wind speed Tree strip 102 Tunnel sprayers 104 Walnut - cultivars 15 Water supply - advisory system WG-Meteo 100 Weather conditions 6 White currant - storage 90 Zinc 102 138 Publications Balkhoven-Baart, J.M.T . - Gaby: Op maat gesneden voorlichting via de computer. Agro Informatica 7(1994)3:- 31-33 Bomen, P.A.; J.A. Jobsen, G. Romeijn, en G.L. Wiegers - Side-effects of 107 pesticides on the whitefly parasitoid Encarsia formosa, studied and evaluated according to EPPO guideline no.142 . Bulletin OEPPO/EPPO Bulletin 24(1994):89-107 Bootsma, J. - Chemisch dunnen noodzakelijk voor regelmaat bij Elstar (Chemical thinning a must for regularity with Elstar). Fruitteelt 84(1994)18:18 - Arbeid adelt, maar moet ook wat opleveren (Labour ennobels but must give good results, too). Fruitteelt 84(1994)34:14 Deventer, P. van, A.K. Minks en J. Woets Bestrijdingsdrempels bladrollers zijn moeilijk te bepalen (Control tresholds of leafrol- lers are hard to determine). Fruitteelt 84(1994)2:18-19. Deventer, P. van, A.K. Minks, J. Woets en K.Jilderda - Further tests on mating disruption of codling moth and leafrollers in apple orchards in The Netherlands. Mededelingen Faculteit te Gent 59(1994)26:671-680 Dijkstra, J. en R. van den Broek Nieuwe doordragende aardbeirassen zijn veelbelovend (The new everbearers are promising). Fruitteelt 84(1994)2:16-17 Kwaliteit doordrager komt dichter bij Elsanta (Quality everbearer is coming closer). Groenten + Fruit, vakdeel Vollegrond 4(1994)2:4-5 Dijkstra, J. en J. de Bruijn -Vroeg stekken noodzakelijk voor een goede trayplant (Early cuttings necessary for a good tray-plant). Fruitteelt 84(1994)13:18-19. Ende, J.E. van den - Waarneming voorjaarsuilen is te verbeteren (Observation of clouded drab moth e.o. can be improved). Fruitteelt 84(1994)8:19. Op maat gesneden voorlichting via de computer (Most specific information via computers). Fruitteelt 84(1994)15:22-23. Geest, van der R. en J.E. van den Ende Bestrijding van de groene appelwants is lastig (Difficult control of common green capsid). Fruitteelt 84(1994)32:20-21. Gendt, C.M.E. van - Rose appelluis: waarnemen en ontwikkeling volgen [wie zoekt kan vinden] (Observati ons of the rosy apple aphid) . Fruitteelt 84(1994)14:16-17. Giezen, M.M. Biologische bestrijding met minder roofmijten (Biological control by lower numbers of 139 preditory mites). Fruitteelt 84(1994)8:16-17. Goddrie, P.D. - Eetkwaliteit resistente appelrassen langzamerhand aanvaardbaar Eat quality of resistant apple cultivars is getting acceptable). Fruitteelt 84(1994)12:29-30 - Elshof en Red Elstar zijn een verbetering van Elstar (Elshof and Red Elstar are an improvement of Elstar). Fruitteelt 84(1994)19:24-25 - Sterk gebloste, virusvrije mutanten verdienen de voorkeur (Red blushed, virus free clones are favourite). Fruitteelt 84(1994)29:14-15 Goedegebure, K., M.J. Groot, S. van Diepen,W . Huberts en H. Bus - Peren. De concurrentiepositie van Nederlandse peren in Europa (Pears. The position of Dutch pears in Europe). Brochure bij Fruitteelt 84(1994)1, pp.26. - Pears. The position of Dutch pears on the European Market. Landbouw Economisch Instituut (LEI-DLO), Mededeling 510, 1994, pp.46. Groot, M.J. - Kwaliteit en produktie bepalen optimale plantdichtheid (Quality and Production determine the optimum planting density). Fruitteelt 84(1994)50:21. Groot, M.J. en A.J.P. van der Waart - Rood en groen wordt goed betaald. Grote prijsverschillen tussen appels van klasse l(Red and green are paid well. High differences in prices between apples of first class). Fruitteelt 84(1994)45:12-13. Groot, M. en A.M.E. Schenk - Nog niet duidelijk welk bedrijfsysteem het meeste oplevert (It is not entirely ciaer which business system is succesful). Fruitteelt 84(1994)8:42-44. Hartingsveldt, H.J. van - Zwartstrook bedekt met witte klaver succesvoller dan gronddoek (Tree strips cover with white clover more succesful than soil cover). Fruitteelt 84 (1994)6:30-31. - Het wordt tijd voor een groenere zwartstrook (It is time for a green tree strip). Fruitteelt 84(1994)19:26 - Van zwartstrook naar groenstrook (From a black to a green tree strip). Fruitteelt 84(1994)50:14-15. Heijne, B. - Onderzoek spuittechniek verlegt accenten (Research spraying techniques changes of form). Fruitteelt 84(1994)44:12-13. Hermon, E.A. van - Eens CCC altijd CCC (Once and for all CCC). Fruitteelt 84(1994)18:16-17 - Snoei na bloei is een goede groeiremmer (Pruning after bloom is a good growth retardant). Fruitteelt 84(1994)19:16-17 Jager, A. de - Foliphos het proberen waard (Foliphos is worth trying). Fruitteelt 84(1994)9:22-23 - Hardheid van Elstar een stevig kwailiteitsprobleem (Firmness of Elstar a big quality problem). Fruitteelt 84(1994)50:12-13 140 Kemp, H. •Veelbelovend e rassen zijn volgend jaar te planten (Promising chrry cultivars available for planting). Fruitteelt 84(1994)12:31-33. • Onderzoek aan pruim staat niet stil (Research with plums is still going on). Fruitteelt 84(1994)13:20-21. • Vruchtdracht en -grootte beïnvloeden de smaak (Crop load and fruit size affect the fruit taste of pear cultivars). Groenten + Fruit, vakdeel Hard- en zachtfruit 4(1994)24- :8-9. - Kwee meer dan een onderstam (Quince, more than a rootstock). Fruitteelt 84(1994)3- 9:12-13. Kemp, H., K. Belmans en J. Verheijen - Results of joint plum cultivar trials in Belgium and The Netherlands. Acta Horticulturae 1994, nr.359 pp.107-109. VIaas, M.P. van der Cox en Boskoop hebben een laag calciumgehalte (Cox and Boskoop have a low calcium percentage). Fruitteelt 84(1994)30:16-17 VIaas, M.P. van der, J.H. Bootsma, E.A. van Hermon en W.A.G.M. Jansen Grondsoort bepaalt succes van calciumfertigatie (Soil determines if calcium fertigation is succesful). Fruitteelt 84(1994)10:14-15 Oosten, A.A. van Kwaliteit kleinfruit krijgt volle aandacht (Attention is paid to the quality of small fruit). Groenten + Fruit vakdeel Hard- en zachtfruit 4(1994)19:4-5. Open middag houtig kleinfruit PFW (Open day cane and bush fruit). Fruitteelt 84(199- 4)19:20-21. Detvan en Tatran, opvallende rassen (Detvan and Tatran, remarkable cultivars). Groenten + Fruit, vakdeel Hard- en zachtfruit 4(1994)26:4-5. Fruitteelt 84(1994)26:- 12-13. Autumn Bliss laat zich niet gemakkelijk verdringen (Autumn Bliss can not be pushed aside easily). Fruitteelt 84(1994)33:12-13. Groenten + Fruit, vakdeel Hard- en zachtfruit 4(1994)33:6-7. Putter, H. de Bewaarrrot niet afdoende bestreden door ULO-bewaring (Storage rot has not comple tely controlled by ULO-storage). Fruitteelt 84(1994)21:18-19. Rot toch probleem bij lange ULO-bewaring (Rot, a problem at long ULO-storage). Groenten + Fruit, vakdeel Hard- en zachtfruit 4(1994)20:8-9. • Risico op scald nog moeilijk te voorspellen (Risks on scald hard to predict). Groenten + Fruit, vakdeel Hard- en zachtfruit 4(1994)30/31:6-7. Roelofs, F.P.M.M. Bij CA-bewaring blijft smaak het beste behouden (Taste remains the best with CA- storage). Groente + Fruit, vakdeel Hard- en zachtfruit 4(1994)1:12-13 Kies voor smaak, kies voor CA (Chose for taste, chose for CA). Fruitteelt 84(1994)2:- 12-13 141 - Schilvlekjes Elstar ernstig probleem (Skin spots Elstar a serious problem). Groenten 4 Fruit, vakdeel Hard- en zachtfruit 4(1994)13:10 - Onverwachtse kwaliteitsproblemen steken kop op (Unexpected quality problem raises its head). Fruitteelt 84(19944)20:16 - Doyenné blijft het best in gescrubde bewaring (Doyenné the best in scrubbed storage) Groenten + Fruit, vakdeel Hard- en zachtfruit 4(1994)35:12-13 - CA-bewaring verbetert de kwaliteit, maar verlengt de bewaarduur niet (CA-storag« does improve the quality but does not extend the storage time). Fruitteelt 84(1994)3 6:12-13 Roelofs , F.P .M .M . en A. Breugem - Kies voor smaak, kies voor CA (Choose for taste, choose for CA). Fruitteelt 84(1994 )2:12-13. Groenten + Fruit, vakdeel Hard- en zachtfruit 4(1994)1:4-5. Scheer, H.A.Th, van der - Meer belangstelling voor biologische bestrijding van ziekten (More interest in biologica control of diseases). Fruitteelt 84(1994)8:40-41. - Schurft blijft problemen geven (Scab remains a problem). Fruitteelt 84(1994)24:20. - Het 'falen' van schurftbestrijdingsmiddelen in 1994 (Scab pesticides failed in 1994) . Fruitteelt 84(1994)50:18-19. - Potential ascospore dose measurements of Venturia inaeqalis applied to the manage ment of primary scab in commercial apple orchards. Norwegian Journal of Agricultura Sciences, Supplement no.17 , pp.69-73. Schenk, A.M.E. - Systeemonderzoek voor resistente rassen van start. Wellicht een systeem waai muziek in zit (System research for resistant cultivars begins. Maybe a promisinç system). Fruitteelt 84(1994)13:25 Schenk, A.M.E., C. Dekker en H. Veijer - Population of mites in three different fruit production systems. Med. Fac. Landbouww Univ. Gent, 59/2b, 1994, pp. 571-577. Schepman, M.A. en M. Jansen - Kleine tuinafrikaan als bestrijder van wortellesie-aaltjes (African Marigold as a control ler of the meadow nematode). Fruitteelt 84(1994)39:14-15. Scholtens, A. - In etappes stikstof bemesten (Fertigation of potassium in stages). Fruitteelt 84(1994) 13:22-23 - Frambozenplanten bewaren (Storage of raspberry plants). Fruitteelt 84(1994)43:14-15 - Rode-bessenteelt in potten (Red currants in container). Fruitteelt 84(1994)48:20-21 Scholtens, A. en P.S. Wagenmakers - Invloed boomgrootte ondergeschikt aan plantdichtheid en plantsystemen (The influence of tree height is not so important as planting density and planting system), Fruitteelt 84(1994)20:22-23. 142 rromp, J. en O. Borsboom The effect of autumn spring temperature on fruit set and the effective pollination period in apple and pear. Scientia Horticulturae 60(19941:23-30. rromp, J. en J.C. Ovaa Spring cytokinin composition of xylem sap of apple at two root temperatures. Scientia Horticulturae 57(1994):1-6. rromp, J., K.A. Visser en J. Dijkstra • Fruit set and the effective pollination period in red currant as affected by nitrogen fertilization and exposure to light. The Journal of Horticultural Science 69(1994):791- 797. Wagenmakers, P.S. Light relations in orchard systems. Proefschrift Landbouw Universiteit Wageningen, 1994, pp.152. /Vagenmakers, P.S., J. van den Boomgaard enJ . Bootsma Meest goedgekleurde appels bij 6000 bomen per ha (The best coloured apples with 6000 trees per ha). Fruitteelt 84(1994)32:22-23. Wagenmakers, P.S. en M. Tazelaar Kiezen voor kwaliteit (Choose for quality). Fruitteelt 84(1994)50:22. Weibel, F.P. en J.A. Devos Transpiration measurements on apple trees with an improved stem heat balance method. Plant and Soil 166(1994)2:203-219 Wertheim, S.J. Hazelaarrassen geschikt voor Nederlands klimaat (Hazelnut cultivars for Dutch climat). Fruitteelt 84(1994)21:21-23. Hazelnut-cultivar evaluation in The Netherlands. Acta Horticulturae 1994, nr.351, pp.71-77. Nieuwe rode-kerseonderstammen in een notedop. Standaard kerseonderstammen verdwijnen (New red cherry rootstocks. Casual cherry rootstocks disappear). Fruitteelt 84(1994)23:11. Nieuwe appelonderstammen in een notedop. Onderstammen gewenst met een groeikracht tussen M.9 en M.27 (New apple rootstocks. Rootstocks desired with a growth between M.9 and M.27). Fruitteelt 84(1994)33:14. Nieuwe pereonderstammen in een notedop. Zwakke kweetypen zijn wellicht bruikbaar. (New pear rootstocks. Dwarfing quince cultivars are probably useful). Fruitteelt 84(1994)33:15. Nieuwe pruimeonderstammen in een notedop. St. Julien A te sterk (New plum rootstocks. St. Julien A too strong). Fruitteelt 84(1994)33:16. Wertheim, S.J. en E.N. Estabrooks Effect of repeated sprays of 6-benzyladenine on the formation of sylleptic shoots in apple in the fruit-tree nursery. Scientia Horticulturae 60(1994):31-39. 143 Wertheim, S.J. en P.S. Wagenmakers - How to increase productivity of future pear orchards. Acta Horticulturae 1994 nr.367, pp.138-151. Wertheim, S.J. en A. Scholtens - Proefresultaten met M.27 als tussenstam. M.27 als tussenstam te gebruiken (Tria results with M.27 as interstem. M.27 can be used as interstem). Fruitteelt 84(1994)2 9:11-13. Wertheim, S.J., J.L. Baarends en H. Kemp - Steenfruitdagen Duitsland 1994. Dit jaar de kersen voor het voetlicht (stone fruit day! in Germany. The cherries were number one this year). Fruitteelt 84(1994)43:16-17. Woets, J. - Zweefvliegen op zoek naar bladluizen (Hoverflies looking for aphids. Fruitteer 84(1994)8:22-23. - Olie en zeep als bestrijdingsmiddelen (Oil and soap as pesticides). Fruitteelt 84(1994) 12:24-25. 144 Bulletins and publications on fruit growing Bulletins of the Research Station for Fruit Growing ir.1 Strawberries grown in the open (Dutch), 80 pp, 3rd. ed., May 1986 f 14.00 ir.2 Glasshouse strawberries (Dutch), 84 pp, 2nd. ed., July 1990 f 14.00 ir.5 Walnut growing (Dutch), 75 pp. May 1981,reprin t f 27.50 ir.6 Hazelnut growing (Dutch), 84 pp, 2nd ed., April 1988 f 16.50 ir.7 From cold stores towards ULO-storage, (Dutch), 72 pp, March 1991 f 14.00 ir.8 Blueberry, cranberry and lingonberry culture (Dutch), 72 pp, March 1991 f 11.50 ir.18 H.A.Th, van der Scheer: Canker on fruit trees (Dutch with an English summary), 66 pp, December 1980 f 16.50 ir.22 S.J. Wertheim: De Peer (Dutch), 344 pp, November 1990 f 75.00 ro order any of the titles listed above, transfer the appropiate amount (prices include jostage by surface mail) to an account of the Proefstation voor de Fruitteelt (postoffice giro account nr. 49 50 17, account with Amro-bank Goes nr.472174878) or by nternational postal money order in Dutch currency, payable to the Proefstation voor de ruitteelt at Wilhelminadorp. 'lease indicate clearly the items being ordered. 145 Publications of the Division Fruit Production of the National Reference Centre for Arabic Farming and Horticulture nr.9 Basis of recommandations for fertilisation of fruit crops grown in the open (soil analysis, leaf analysis) (Dutch), 24 pp, June 1992 f 11.5C nr.10 Conscious use minerals use of fertilizers in orchards (Dutch), 40 pp, 2nd., ed., May 1993 f 12.5C To order any of the titles listed above, transfer the appropiate amount (prices include postage by surface mail) to an account of the Informatie en Kenniscentrum, afdeling Fruitteelt (postoffice giro account nr. 35 46 77) or by international postal money ordei in Dutch currency, payable to the Informatie en Kennis Centrum, afdeling Fruitteelt al Wilhelminadorp. Please indicate clearly the items being ordered. Publications of the committee for the composition of the list of fruit varieties (C.R.F.) 18th list of Fruit Varieties 1992, (Dutch), 288 pp, December 1991 f 17.3C To receive this list please send an international postal money order for f 17.30 to NFO, The Hague (postoffice giro account nr. 51 08 83 or, account Rabo-bank The Hague, nr. 2003 01 357) or to the Kononklijke De Boer Boekhoven (post office giro account nr. 81 26 or account ABN/AMRO hilversum, nr. 5501 48 143). The price includes postage b\ surface mail. 146