RESEARCH STATIONFO RFRUI T GROWING 4475A N WILHELMINADORP,TH ENETHERLAND S

ANNUAL REPORT1978

Information contained inthi s report may notb ereproduce d intota l ori n partwithou t permission PriceDf .7, - CONTENTS

page REMARKS ON THE BRANDS OF PESTICIDES AND HERBICIDES 5

DONORMEMBER S 6

BOARD 7

STAFF 8

POMOLOGY SECTION: !' Research on top fruit (North-Holland and slender spindle— summer 11 pruning— planting systems— planting-hole treatments) Regulation of fruit-set, fruit growth, fruit drop and vegetative growth 14 (Vegetative growth— defoliation) Generative development (Chemical thinning— fruit set improvement— 17 pollination— percentage of pollinators) Screening unusual fruit crops 20 Virus research and clonal selection in fruit trees 21 Research on culture infruit-tre e nurseries (Selection inrootstoc k 21 clones) Rootstocks and interstocks for pit and stone fruits (Apple— plum) 23 Fruit variety trials (Apple— pear— plum— second screening trials in 25 experimental orchards)

SMALL FRUIT SECTION: 29 Culture experiences with strawberries (Irrigation inplasti c tunnels— 29 comparison of some Gorella 'clones') Variety testing of strawberries (Plastic tunnels— variety trial in the 30 open— cold-stored waiting field plants (for a late harvest)— everbearing varieties) Culture experiments with raspberries and currants (Raspberry— red- 32 currants— black-currants) Variety testing of raspberries,currant s and blackberries (Raspberry— 33 red-currant— black-currant— gooseberry — blackberry)

SOIL FERTILITY SECTION 38 Soilmanagemen t experiments 38 Influence of nitrogen onyiel d and quality of fruit crops 39 Relationship between potassium contents inappl e leaves and soil 41 Bitter pit in apple 41 Trickle irrigation 43 Chemical weed control ^3 PHYSIOLOGY SECTION: 45 Investigations into factors underlying the relationship between the 45 vegetative and generative development of fruit trees (Growth regulators — effect of air and root temperature and light intensity on the behaviour of budded apple rootstocks— seasonal variations in theminera l compo­ sition of xylem sap of apple— effect of a few environmental factors on flower-bud formation in apple) Pre-harvest physiology of fruits inrelatio n to fruit quality (Effect of 46 relative airhumidit y (R.H.)o n shoot and fruit growth and on the mineral composition of leaves and fruits of apple— effect of soil moisture level on shoot and fruit growth and on theminera l composition of leaves and fruits of apple)

PLANT PATHOLOGY SECTION: Apple (Canker— fruit rot,storag e diseases— phytotoxicity— powdery 48 mildew— scab) Apple and pear (Crown gall) 50 Strawberry (Alternaria leaf spot— red stele) 51

ENTOMOLOGY SECTION: 52 Integrated pest control inorchard s (Pit fruit— strawberry) 52

ECONOMIC SECTION: 54

Production costs of fruit-tree growing on a fruit holding 54

LIST OF CHEMICALS 56

PUBLICATIONS 58 REMARKSO NTH E BRANDSO FPESTICIDE SAN DHERBICIDE S

The dosages mentioned for pesticides and herbicides in this report refer to the commercial products.Trad e names of products have been used for the sakeo f convenience,bu t thismake s itunavoidabl e that insom e cases similar products on themarke t under other trade names are not mentioned. No endorsement of named products is intended.A list of most of the commercial products mentioned in this report and their active ingredients isgive n onpag e56 . Some of the experiments described in this report arebein g carried outwit h chemicals and/or concentrations notye t legally approved. DONOR MEMBERS

Thosewh o are interested in thewor k of the Research Station and wish to keep inactiv e touchwit h and support its research, are invited tobecom e donor members. Donor memberswil l receive theAnnua l Report and other publications of the Research Stationwithou t charge.Th eminimu m subscription for donor membership is 25 guilders for private individuals inTh e Netherlands,5 0 guilders for foreign private individuals and 50 guilders for institutions,annually . Checks on international postal money orders should be made payable to Proefstation voor de Fruitteelt atWilhelminadorp ,wit h the indication 'Donor Subscription'. BOARD (31thDecembe r1978 )

Board ofth eFoundatio n Research Station forFrui t Growing

Executive committee:

IrJ .Minderhoud , chairman E.H.M.Jongerius ,vice-chairma n J.Kakebeeke , secretary J.L.Nijsten , treasurer IngJ.S.J.M . Mulders

Remaining members:

IngJ .Burge r N.J.J. Costong s Z. Houter W.d eJage r CR.T. Leenders B. Leijs J.A.M.Muster s L.J.M.E.va nWagenber g

Advisor :

IrH .Sytstr a STAFF (31thDecembe r1978 )

RESEARCH STATION FORFRUI T GROWING

Director: IrR.K . Elema Deputy director:D rI rS.J .Werthei m

Pomology Section DrI rS.J .Werthei m (head)

Research on orchard trees Dr IrS.J .Werthei m (research worker) J.L. Baarends (atth esam e time foreign excursions) M.L. Joosse F. Nijsse Research on plant material DrI rH.J .va nOoste n (researchworker ) J.M. deGroen e Fruit Variety testing IngP.D .Goddri e

Small Fruit Section IrJ .Dijkstr a (headan dresearc h worker) A.A.va nOoste n

Soil Fertility Section Dr IrP .Delve r (head andresearc hworker , stationed byth eInstitut e forSoi l Fertility (IB)a tHare n (Gr.))

Laboratory J.Oel e (head) G. Kenson Miss M.C.M. Smits

Field- and pot trials IngP.J .Boldin g J.d eSchippe r Physiology Section Dr J. Tromp (head and research worker)

Laboratory Miss J.C. Ovaa (head) Mrs. E.J.M.va n der Borgt-Satink Field- and pot trials Ch.A.R. Römer J. de Schipper

Entomology Section Drs D.J. de Jong (head and research worker, stationed by the Institute of Phytopathological Research (IPO)a t Wageningen) H. Beeke W. Remijnse

Plant Pathology Section Drs H.A.Th,va n der Scheer (head and research worker) J.P.A.va n Dieren H.J. Wondergem (stationed by the National Board ofAgricultura l Research TNO at The Hague)

Economics Section J. Goedegebure (research worker, stationed by theAgricultura l Economic Research Institute (LEI)a t The Hague)

Administrativean dclerica l staff Miss J. Hamelink (head)

Adminis tration Mrs. A.M.Th,va n de Rijt-Mateijsen (secretary) Mrs. T.L. Buizer-Schuit Miss J.N. Verrijzer Housekeeping Mrs. E.M.A. van Iwaarden-Asselman Miss P.C. de Smidt

Staffworker/ed i tor/1 ibran 'a n Ing Tj. van der Kooi Statistician J.P.A. van Dieren

Technician J. van Dalen

Experimental Garden Wilhelminadorp J.J. Lemmens (manager) Top Fruit Section P. Proost (deputy manager) A.A. Janse M.C. van Maris A.J.P.va nd e Waart A.d e Witte Small Fruit Seation L. Nijsse (deputy manager) K. de Koei je r

NATIONAL FRUIT ADVISORY SERVICE National Fruit advisor Ir. R.K. Elema Coordination regional experiments Ir J. Dijkstra (head) Ing J.H. Bootsma (experiment garden at Kraggenburg) A. Scholtens (experiment garden at Geldermalsen) Economist vacancy General specialist top fruit vacancy General specialist small fruits J. Blommers Soil specialist IngA . Pouwer (stationed by the National Soil Advisory Service in the Horticulture at Wageningen)

10 POMOLOGY SECTION

S.J. Wertheim,H.J . van Oosten,P.D . Goddrie and J.J. Lemmens

Research onto pfrui t

S.J. Wertheim and J.J. Lemmens

North-Holland and slender spindle

On the cultivars Discovery, Cox's Orange Pippin,Rod eBoskoop , and Winston a comparisonwa s started at thebeginnin g of 1977betwee n slender and North- Holland spindles.Som e results are mentioned here forDiscover y and Cox's Orange Pippin. The trial onDiscover ywa s started with four-year-old trees on M.9 planted at 3.25 x 1m atYerseke . In 1977 the slender spindles yielded more thanNorth - Holland spindles.Th e former gave 7.6 kg per tree, the latter 4.1. This result is logical, since North-Holland spindles are pruned more drastically and possess less crownvolume .Frui t setwa s about equal forbot h three shapes.Frui t size was slightly better onNorth-Hollan d spindles (99 and 104 go r 61 and 66%k g of fruits larger than 65 mm).Averag e largest crown diameters,measure d in November 1977wer e 1.60 m (slender spindle) and 1.30 m (North-Holland spindles). After pruning these figureswer e 1.60 and 1.10 m. The new method of pruning induced more vigorous growth. Slender spindles gave in 1977 7.7 m total shoot growth per tree,North-Hollan d spindles 13.2m . Both thenumbe r of shoots per tree (40.0 and 51.8) and the average shoot length (19.1 and 25.6 cm)wer e increased. The North-Holland pruning required more cuttings (14.5 as against 26.9 per tree). In 1978 the slender spindles had more flower clusters, thanks to their larger volumes (330.6 as against 229.9 per tree), more fruits per tree (34.1 as against 22.3), and more kg (3.6 as against 2.1 per tree). Again fruit setwa s about equal.Now , fruitweigh t was greatest on the slender spindles (105 as against 92 go r 73 as against 59%k g of fruits larger than 65mm) .Mos t impor­ tantwa s the detrimental effect of the new pruning method on fruit colouring. For slender spindles 35%o f the kgwer e well-coloured fruits,fo r North-Holland spindles thiswa s only 7. On Cox's Orange Pippin the comparison started with trees onM. 9 at Ovezande in thebeginnin g of their third leaf. Planting distancewa s 3.25 x 1.25 m. The North-Holland pruningmetho d reduced the treevolume ,whic hwa s expressed in the number of flower clusters per tree (238.9 and 131.1). Fruit setwa s poor due to spring frost and yield was 24.1 against 24.9 fruits per tree (3.4an d 3.7 kg per tree). Average fruit weight was slightly higher on the North-Holland spindles (142and14 8g or 86 and 91%k g of fruits larger than 65mm) .Frui t colourwa s detrimentally affected (from4 2 to 28%k gwit h well-coloured fruits). Tree crown diameters after pruning in thewinte r of 1977/78wer e 1.70 and1.30m .Growthwa s not stimulated much, from 27.6 to 30.2m total annual growth per tree.Thi s increase was due to longer shoots (35.3 and 40.7 cm)an d not to number of shoots per tree (78.0 and 74.2).Here , too, North-Holland pruning was more laborious (5.0 as against 16.2 cuts per tree).

11 In 1978yiel d was lowdu e to insufficient cross-pollination in the orchard. Slender spindles had 358.3 flower clusters per tree,North-Hollan d spindles 327.2. Yield was in the same sequence 25.0 and 19.4 fruits per tree (5.0an d 3.6 kg per tree). Fruit setwa s about equal.Al l fruitswer e large (201 and 186 g)an d therewa s no difference in fruit colour between the two spindle types (27 and 28%k g ofwel l coloured fruits). After picking, the average largest crown diameters were 2.30 and 2.00 m. In the next annual report resultswit hRod eBoskoo p and Winstonwil l be summarized.

Summer pruning

In the experimental garden atNumansdor p summer pruning was investigated in theyear s 1976-1978.O n eight-year-old trees onM. 9 of Cox's Orange Pippin, Schoneva nBoskoop ,an d Winston the following treatments were carried out: 1.winte r pruning 2. all shoots halved -, 3.al l shoots removed \ directly after growth cessation 4. all one-and-a-half-year-old twigshalved" ^ 5. all shootshalve d -, 6. all shoots removed \ threeweek s after growth cessation 7. all one-and-a-half-year-old twigshalve d' The summer treatments 2t o 7wer e followed by additionalwinte r pruning. The results of Cox are omitted because of thevariabilit y of the trees. With Schoneva nBoskoo pTreatment s 4,5 , and 7an d in 1978 all summer-pruning treatments were disadvantageous for yield, expressed innumbe r of fruits per tree.Expresse d ink g per tree,Treatment s 3, 4,6 , and 7wer e most detrimental. The number of kg per tree summed up for the three yearswer e for the seven treatments: 66.1,66.7 ,59.0 ,62.3 ,56.3 ,an d 56.0,respectively . The loss in yield of the four most detrimental treatments was brought about by the smaller tree crownvolum e that arose gradually. Although Treatments 3,4 , 6, and 7wer e alsoharmfu l for the fruit size in 1977 and 1978,thi swa s of no importance with this larged-fruited cultivar. Summer pruning had no effect on theoccur ­ rence ofbitte r pit or core flush during storage. For Winston the results are given inTabl e 1.

Table 1.Result s of comparison ofwinte r pruning and summer pruning plus additional winter pruningwit h Winston. Data are means of twelve trees per treatment.

Treatment Fruits/ tree Kg/tree Mean fruitweigh t g (seetext ) 1976 1977 1978 1976 1977 1978 Total 1976 1977 1978

1 123.7 188.9 173.0 16.1 20.7 19.9 56.7 130 109 115 2 138.8 176.3 155.4 17.6 19.7 18.4 55.7 127 112 119 3 131. 0 137.7 142.3 16.2 14.6 13.9 44.7 123 106 98 4 123.0 169.0 157.3 15.7 19.0 18.1 52.8 128 112 115 5 125.1 155.2 138.1 15.7 18.0 16.6 50.3 126 11 6 120 6 129.0 112.3 101.7 15.5 12.0 10.4 37.9 120 107 102 7 117.1 174.2 154.3 15.0 19.0 17.8 51.8 128 109 115

In 1976 Treatments 3 and 6ha d asmal l detrimental effect on fruit size.Frui t number was not affected thatyear ,whic h is logical since only non-bearing wood was removed inJul y and August. In 1977 all summer-pruning treatments,especial -

12 ly3 an d6 ,wer e detrimental toyield . In197 8th eresult s were thesame .I n thatyea r again treatments 3an d6 reduce d fruit size. Apparently, theannuall y repeated removal ofal lshoot s inth egrowin g season isver y harmful hothfo r fruit number andfrui t size. This finding indicates that growers mustb ecare ­ fulwit h summer pruning, although here treatments were exaggerated. Halving shoots didno tappea r very detrimental.Treatment s 4an d7 appeare d more favourable than3 an d6 becaus e halving one-and-a-half-year-old wood in 1976, made summer pruning hardly necessary inth efollowin g 2years .Th eformatio no f new shootswa sgreatl y reduced.Fo rexample ,i n197 8treatment s 2an d5 required onaverag e 61.8cut s pertre e inth esummer , treatments 3an d6 50.9, but treatments 4an d7 onl y9.4 .Thu s adrasti c summer pruning canmak eth e trees small atth eexpens eo fyiel d andfrui t size.

Planting systems

The planting-system trials onParcel s 5an d1 2wer e again followed in 1978. Because theyiel d uptil l 1977ha sbee n extensively described inth e197 7 report (p.32-33) , results of197 8wil lb eomitte d here.Moreove r they didno t reveal anyne wvie w points.Wort h mentioning istha t in197 8o nParce l5 detailed light measurements were madeb ytw oresearcher s ofth eEas t Mailing Research Station (J.W.Palme r andD .Avery) . Thesewer e followed laterb y detailed crop analyses atthei r ownresearc h station.Th eresult s ofthi s research willb epublishe d elsewhere.

Planting-hole treatments

Trees ofth eplanting-hol e experiment with Jonagold onM. 9i nParce l13 a planted insprin g 1977gav e their first crop in1978 .Th egrea t differencesi n growth between thevariou s treatments (seeAnnua l Report 1977,p .33-35 )wer e expressed inyiel d differences (Table 2).

Table 2.Yiel d ofJonagol d onM. 9i nth esecon d growing season after various planting-hole treatments andgift s ofwater . Values aremean s of3 2 trees pertreatment .

Treatment Fruits/ Kg/ Meanfrui t tree tree weight g

Untreated 12.4 3.1 240 ii +trickl eirrigatio n 21.0 4.4 209 Mushroom compost 12.3 3.1 248 H H +trickl eirrigatio n 20.1 4.6 233 Pottingcompos t 19.3 4.1 214 II H +trickl eirrigatio n 25.2 5.7 233 Pottingcompos t+Mushroo mcompos t 21.6 5.2 239 H H +11 H +trickl eirrigatio n 30.7 6.9 225 Trickle irrigationwa scontinue d in197 8(i nth eappropriat e treatments).I n total56 01 o fwate rwa ssupplie d pertre e during thegrowin g season. Yieldwa shig h eveni nuntreate d trees. Ground coverwit h mushroom compost around thetrun k after planting hadn oeffec to nyield .Th eus eo f2 01 pottin g compost inth eplantin g holeha da positiv e effect. Trickle irrigationha dth e strongest effect onyield , especially incombinatio nwit h potting composti n theplantin g hole anda cove r ofmushroo m compost around thetree s topreserv e moisture.

13 Regulation of fruit-set, fruit growth, fruit drop, and vegetative growth

S.J. Wertheim

Vegetative growth

Growth retardation When in the spring of 1977 Cox's Orange Pippinwa s severely damaged by spring frost,i twa s expected that treeswoul d show vigorous growth,becaus e of the off year. Therefore,a n experimentwa s started ina n orchard atNisse ,wher e SADH (Alar-85)an d ethephon (Ethrel-A)wer e applied.Alar-8 5 (0.30%)wa s applied early (9June )an d late (12 July), 0.20% Ethrel-Awa s only applied on the latter date. The treatments were also combined. Indeed, the trees had hardly any fruits,bu t growth remained on anorma l level.Th e retardants had no visual effects. In 1978 it appeared that the early SADH-treatments and the ethephon had promoted flower-bud formation,especiall y after an early SADH plus an ethephon treatment. This treatment resulted in 491.1 flower clusters per tree as against 387.6 on untreated trees.Th e heavier flowering,however , did not lead toyiel d improvement, although fruit setwa s low as treated treesha d a somewhat lower fruit set.Henc e the aim of the trial,growt h retardation,wa s not attained and the treatments did not have any effect in theyea r after treatment.

Side-shoot formation in fruit-tree nursery OnSchon eva nBoskoop ,budde d inAugus t 1977 onM.9 ,th e effect of removal of young leaves during the 1978growt h was studied.Young , light green leaves were removed by hand at averageheight s of 55 cm (21 June), 65 cm (30June ) or 75 cm (13 July). These partial defoliations were done inal l possible combinations. The number of leaves removed was 6.2, 5.8 and 6.6 perbud , respectively. However, for a second or third successive defoliation, fewer leaves were removed. For example,whe n defoliation took place at5 5 and 65 cmheigh t the second time,onl y 2.4 young leaves had tob e removed. On 21 June,al l young side shoots up to 35 cm above the unionwer e taken away from all trees to stimulate shoot formation higher up.Pe r bud 6.1 side shoots were removed with an average length of 3.9 cm. Young-leaf removal had some effect,bu t less than in 1977.Fo r example, untreated trees had 2.5 side shoots per tree and those of thebes t treatments 3.7 (twice defoliated at5 5 and 65 cmo r at 55 and 75 cm).Tre e lengthwa s not affected much by the treatments.Untreate d budswer e 137.9 cman d those of the most 'inhibiting' treatments 128.5 cm (twice defoliated at 55 and 75cm) . In asecon d experiment onWinsto n onM. 9 the effect of side-shoot induction and removal of low side-shoots,bot h chemically orb y hand,wa s investigated. Removal of low shoots took place on 21 Junewhe n the average bud length was 38.1 cm.Pe rbu d 4.7 side shoots were broken off,whic h had an average length of 5.2 cm.Thi swa s done till 30 cm above the union.Chemically , these low side shootswer e controlled by a spraywit h0.30 %Amex-A82 0+ wetter . Side-shoot induction took place on 17Jul y when thebud swer e between 54 and 55 cm long. Inductionwa s by hand,youn g tip leaves being removed (5.5 leaves perbud) . Thiswa s repeated on 27 July at 63.5 cmbu d length.A t that time 3.3 young leaves perbu d tipwer e removed. For chemical induction thewhol e buds were sprayed with 0.12% FR 570/3.Al l treatments are mentioned in Table 3.

14 Table 3. Growth data of trial to improve plantmateria l ofWinsto n onM. 9 in the fruit-tree nursery. Values aremean s of eleven trees per treatment.

Treatment Tree Total Number si de shoots Mean shoot Trunk (see text) length length l 10 cm/tree length cm circumfe­ cm side rence at Total è 30 cm ** shoots 25c m abo­ à 30 cm ** ve union

1. Untreated 109.0 a 25.9 a 7.0 a 0.7 a 35.6 ab 4.8 a 2. removal low shoots 106.1 ab 71.2 b 2.7 d 2.3 ab 31.3 abc 4.3 a 3. spraying low shoots 106.5 ab 68.4 b 2.9 d 1.9 ab 35.8 ab 4.7 a 4. 2x leaf removal 104.0 bc 20.1 a 5.6 abc 0.6 a 24.6 ac 4.4 a 5.0.12% FR 570/3 98.6 d 15.4 a 6.2 ab 0.7 a 24.1 ac 4.4 a 6. 2+4 101.3 cd 71.3 b 2.8 d 2.4 ab 30.2 abc 4.3 a 7. 2+5 99.0 d 91.5 b 4.3 bed 3.6 b 25.8 ac 4.3 a 8. 3+4 101.9 bed 70.8 b 3.6 cd 1.8 ab 39.0 b 4.5 a 9. 3+5 97.9 d 80.8 b 5.4 abc 3.6 b 22.4 c 4.6 a

The data of Table 3 indicate thatvariou s treatments reduced side-shoot for­ mation at a good height (à 30 cm above the union). Bud length was reduced by the treatment,bu t not always statitiscally significant. Trunk circumferencewa s not clearly affected. Side-shoot formationwa s stimulated mostly by removal of too low shoots,especiall y when combined with aF R 570/3 spray (Treatments 7an d9 inTabl e 3). Side-shoot induction alone (Treatments 4 and 5)ha d noeffect , possibly because vigour in 1978wa s rather low. Invariou s commercial orchards, treeswer e observed which had been induced to form side-shoots in the fruit-tree nursery. In a first trialwit hSchon eva n Boskoop onM. 9 such treeswer e planted in the spring of 1976.Unbranche d trees (untreated in the nursery in 1975)an d branched trees (0.15%M& B 25,105 in the nursery)wer e involved. First cropwa s obtained in 1977.Branche d trees then gave 6.4 apples per tree (1.9 kg),unbranche d ones 0.7 fruits (0.2kg) .I n 1978 the former gave 65.8 fruits (14.0 kg), the latter 59.3 (12.3kg) . In a second trialwit h Winston onM. 9 therewa s little difference between treated and untreated treesbecaus e the untreated trees in the nursery still possessed quite a number of low feathers,whic h contribute to early production. In 1977 trees treated with M&B 25,105 gave 18.9 fruits per tree (2.4kg ) and in 1978 20.3 (3.7kg) .Fo r untreated trees these values were 14.8 (2.0kg ) and 16.7 (3.2 kg), respectively. In two other trials,on e year younger, Belle de Boskoop and Jonagold both on M.9wer e involved. Belle de Boskoop untreated in the fruit-tree nursery gave 3.4 fruits (1.0kg )pe r tree in the second growing season in the orchard. Chemically treated trees (with M&B 25,105) 6.1 fruits (1.6kg) .Fo r Jonagold these figureswer e in the same sequence 6.4 fruits (1.3kg ) and 8.7 fruits (1.9kg) . Although all differences mentioned are small,on e must bear inmin d that they have tob emultiplie d by the current high number of trees per ha (± 2000). Besides,branche d trees obtained from the nursery require nobendin g down of side shoots. defoliation

In acommercia l fruit-tree nursery a few defoliants were tested. In the trial Harvade, a cotton defoliant,wa s compared with the two chemicals that gave some effect in 1977,viz .ethepho n andWK-surfactant . The concentrations for the

15 three chemicals applied were 0.10%, 240 ppm, and 2.0%respectively . The sub­ stanceswer e sprayed on Cox's Orange Pippin and Schone van Boskoop,botho n M.9. The treatments involved are mentioned in Table 4.

Table 4. Results of defoliation trialwit h apple.Value s are means of 15 trees per treatment.

Treatment Cox's Orange Pipp in Schone van Bo skoop 18 October 30 October 18 October 30 October leaf leaf leaf leaf leaf leaf damage drop drop damage drop drop * ** ** * #* **

1. Untreated n 1.2 a 3.5 ab n 1.0 a 1 .4 a 2. Harvade 1 3.1 b 4. 1 bc n 1.0 a 2.0 ab 3. Ethephon n 1.1a 3.5 ab n 1 .0 a 1.4 a 4. WK-surfactant m 3.7 b 5.0 c m 1.1a 2.5 b 5. 2+3 1 3.5 b 4.2 bc n 1.0 a 2.4 b 6. 2+4 s 1.2 a 1 .9 a s 1.5 a 2.9 b 7. 3+4 m 4.1 b 5.0 c 1 1.1a 2.7 b 8. 2+3+4 s 1.2 a 2.1 a s 1.3 a 2.5 b

* n =no ,1 = light,m =moderate , s= severe leaf burning. ** 1= no ,5 = 100%lea f drop. Values followed by the same letter(s) dono t differ significantly (P 0.05).

Sprayingwas doneo n6 Octobe r(15°C ,80 %humidity ). O nSchon eva nBoskoo pa secon dtreat ­ mentwa s carried out on 20Octobe r (11°C,85 %humidity) ,bu twit h the three chemicals separately and the combinations Harvade + ethephon andWK-surfactan t + ethephon. The other two treatmentswer e not repeated,becaus e the first spray had already burnt all leaves completely.Alread y on 6Octobe r Cox showed some naturallea fdro pan ddiscoloration ;Schon eva n Boskoop,however ,di dnot .Her eal l leaveswer e green and still firmly attached to the plant.Lea fdamag ean ddro pwa s observed on 18an d 30Octobe r (see Table4) . On 18October ,Co x trees of the treatments 2,4 ,5 , and 7clearl y showed leaf drop.Harvad e combinedwit h WK-surfactant (treatments 6an d 8)gav e total browning of all leaves.Thi s had occurred so rapidly that separation processes could not occur. The dead leaves remained on the trees aver y long time.O n 30 October WK-surfactant,whethe r or not combined with ethephon,ha d caused complete defoliation. Since the trees do not show an after-effect of these treatments in 1979,bot h arewort h further testing. OnSchon eva nBoskoo pther ewa s no effect of the treatments on 18Octobe r and a slight effect on 30October , in spite of two treatments.Here , tooWK-surfac ­ tant proved most active,whethe r or not combined with the other two substances. Aswit h Cox the combination Harvade +WK-surfactan t gave complete leaf burning. However,her e itdi d not reduce leaf'drop . For the present thebes t chemical to test further is theWK-surfactant . Given the difference in reactionbetwee n the two cultivars, itma yb ebette r to apply defoliantswhe n natural leaf drop has commenced.

16 Generative development

Chemical thinning

Benoni For the fifth successive year chemical thinningwit h ethephon (0.30%Ethrel-A ) was investigated on the same Benoni trees onM.9 . Ethephon thinning plus additional hand-thinning was compared with hand thinning alone.Al l experimental trees flowered well in 1978,hand-thinne d trees having an average of 470.6 flower clusters per tree,chemica l thinned ones 366.5. Ethephonwa s applied on 5 May,b ywhic h date 20%o f the flowers had opened.Untreate d treeswer ehand - thinned on 26, 29,an d 30May , sprayed ones on 30May .Fro m the former 2215.2 fruitletswer e thinned, from the latter on average 438.0. In time, it took 24.5 hours to thin the 22unspraye d trees against 10hour s for the same number of sprayed trees.Henc e ethephon thinned succesfully. Ethephon-treated treeswer e sprayed twicewit h anNA A stop-drop spray (31 July, 8August) , untreated trees once (8August) . At picking (23August ) unsprayed trees yielded 185.5 fruits (28.2kg ) per tree and 1.7 fruits per tree had fallen off.Mea n fruitweigh t amounted to 152g . For the chemically thinned trees these valueswer e 117.8 fruits (19.4 kg), 1.5 fruits and 165g . Grading showed that from purely hand-thinned trees 80.2%fruit s had a diameter larger than 70mm ,wherea s with ethephon-sprayed trees this percentage was 91.0.Pe r treeyiel d of these large fruitswa s 22.6 and 17.7kg .Thu s ethephon reduced production. It remains tob e seen,however ,whethe r all untreated treeswil l have anon-yea r in 1979.

Fruit set improvement

Cox's Orange Pippin Ina poorly cropping commercial orchard with Cox's Orange Pippin onM.9 ,w e tried to improve fruit set chemically for the second year on the same trees.A mixture of 200 ppm gibberellic acid (GA3)plu s 10pp ma-naphthalen e acetic acid (10 ppm)wa s applied once or twice to the trees.Th e first sprayingwa s on 24 Maywhe n the treesha d 50%wor n flowers on the oldwoo d and the one-year-old twigs had only 50%ope n flowers.Th e second spraywa s on 7June .Th e experimen­ tal trees did not flower equally. The treatments in 1977 reduced flowering in 1978. Untreated trees possessed on average 677.0 flower clusters per tree,onc e sprayed trees 584.7, and twice treated 485.0. Both 1978 treatments were equally successful and increased yield, although not enough. In figures;untreate d trees yielded 34.7 fruits per tree (4.3kg) , a very poor crop,mea n fruitweigh t was 125 g. Once treated trees gave 60.1 fruits (7.5kg ) likewisewit h a fruitweigh t of 125 g. For twice sprayed trees these figureswer e 64.8 (7.0 kg), and 108kg , respectively. Per 100 flower clusters fruit set came to 5.1, 10.3,an d 13.4 fruits,respectively . The per­ centage ofk g of fruits larger than 65m mwa s 80.7,80.3 ,an d 70.0.Pe r tree yield of these fruitswa s in the same order 3.5,6.1 , and 4.9 kg. As in 1977,on e spraywa s better than two.Lookin g at the two years together, we find thatuntreate d trees gave 10.4k g (ofwhic h 8.5 kgwit h fruits larger than6 5 cm)an d once sprayed trees 18.2k g (13.0k g large fruits). Although, this increase inyiel d is considerable, it isno t remunerative, given the price of GA3.

17 Pollination

Varietal crossings In 1978,man y hand pollinations were madewit h different apple cultivarst o test their pollenfo rsuitabilit y forcros s pollination.Th eresult s aregive n as follows:O feac h cross first themothe r cultivar isgive nan dthe nth e pollinating cultivar. Then follows thenumbe r offruit s atharves t per10 0 pollinated flowers (i.e.th eactua l flower number involved percross) .I n brackets thefrui t numbero fth esam e number offre e pollinated flowers onth e same trees ismentioned . Invariou s cases anumbe r ofcrosse sha dth esam e free-pollinated control. Lombarts Calvillex Discover y 34(37), xElsta r 39(37), xOdi n 70(37), x Summerred 54(37), xWinsto n 28(37). Lombarts Calville xGloste r 29(28),x Melrose 48(28), xSepte r 50(28), xZoet e Oranje 45(28). Sofo rLombart s Calvilleal lcultivar s involved have suitable pollen. Elstar xGloste r 53(7),x Jonatha n 35(7),x Melros e 54(7),x Tydeman' s Early 65(7). Elstarx Laxton' s Superb 14(10), xLombart s Calville 25(10), xOdi n 42(10). Elstar xSummerre d 49(25). Soi nth efirs t twoserie s free pollinated flowersha da poo r set,bu tno ti nth ethir d series.Excep tfo rLaxton' s Superb, all other pollinators gavea goo d resulto nElstar . Jonagold xMelros e 42(22), xOdi n 41(22), x Summerred 0(22),x Zoet e Oranje 41(22). So,i n this series Summerred pollen failed completely. Jonagold x Septer 12(30), xTydeman' s Early 26(30). Here,th eresul twit h Septerwa sno t very impressive. Odinx Elsta r 82(17), xLaxton' s Superb 61(17), xLombart s Calville 93(17). Odinx Gloste r 91(12), xJonatha n 74(12), xSummerre d 69(12), xTydeman' s Early 79(12), xZoet e Oranje 84(12). So,Odi n reacted excellently oncros s pollina­ tionwit h allcultivar s used. Winstonx Discover y 38(18), xLombart s Calville 55(18), self pollination 1(18). Winstonx Jame s Grieve 36(22), x Summerred 22(22). Hence,al lfou r cultivars used appear suitable forWinston .Winsto ni sfurthe r almost fully self-incompatible. Laxton's Superb xElsta r 75(30), xOdi n 60(30), xSummerre d 64(30).Al l three cultivars gavea ver y good seto nLaxton' s Superb. Melrose xLaxton' s Superb 29(57), xOdi n 69(57). Free pollinated flowerso f Melrose gavea hig h set.Laxton' s Superb pollen could notsurpas s this, Odin could. Gloster xLaxton' s Superb 65(86), xOdi n 90(86). Gloster flowerswhic h were left tofre e pollination almost allse tfruit .Thi s result isi nagreemen t with thehig h productivity ofthi s cultivar. Zoete Oranje xLaxton' s Superb 45(23), xWinsto n 30(23), self pollinated 2(23). Hence,bot h cultivars aresuitabl e forthi s late flowering sweetapple , which ispracticall y self-incompatible. At last afe wsingl e crosses.Zoet eErmgaar d xElsta r 35(45), andDiscover y self-pollinated 0(21). So,th elatte r isa self-incompatibl e cultivar. On pear three crosseswer e made,viz .Doyenn éd uComic ex Cond o 6(1);Cond o x Doyennéd uComic e 11(6)an dx Conferenc e 7(6).Cond o isa Dutc h crosso f Conferencex Doyenn éd uComice .

Malus pollinators In 1978th erol e of Malus pollinator grafts intw ocommercia l orchardswa s again followed.O nCox' s Orange Pippin trees atWissenkerke , Malus 'Hillieri' was investigated,an da tLewedor p 'Aldenhamensis'.Th egraft swer e madei n spring 1974o nth eto po fth etree s sotha t therewer e three treatmentsi n four replicates.Th etreatment s were:n ografts ,on egraf t forever y sixtree s

18 and one for every three trees.I nAugus t productivity was estimated by Dr. Winter's method.A t 2.5 m distance from the trunk all fruitswer e counted that couldb e seen on a tree through a specially designed tube.A countwa s made for theeas t andwes t sides of the trees separately. The average number of fruits per observation in the control plotswa s 4.4, in theplot swit h one graft for every six trees 4.6, and in thebes t pollinated plots 4.7.Thi s difference was of no importance. InLewedor p these figureswer e 4.9, 4.6, and 5.3,respective ­ ly.Here , too,n o effect of the grafts could be established. In an orchard with Belle de Boskoop onM. 9 atBorssele ,wher e in the spring of 1974 trees of Malus 'Liset'o nM.2 6 had been interplanted, yield was esti­ mated in 1978.I n this orchard nine Boskoop rows occur next toeac h other.Th e Malus treeswer e planted in such awa y that the five middle rows of the plots were six trees long. In these plots 0, 10,o r 33% 'Liset' pollinator was intro­ duced; each density in three replicates.U p till 1977n o effect of thepolli ­ nators had ascertained. In 1977 the number of fruits per observation (asmen ­ tioned above)wa s 11.3 in the control plots, 10.1 in the 10%plots ,an d 11.4 in the 33%plots .I n 1978,however , aneffec t of 'Liset'o n Boskoopwa s visible. In that year the number of fruits per observationwa s 12.4,15.9 ,an d 17.4, respectively (eachvalu e is themea n of 90 trees).

Percentage of pollinators

Apple On Plot 23 of the experimental garden atWilhelminador p Cox's Orange Pippin trees onM. 9wer e planted in the autumn of 1971,wit h Golden Delicious trees as pollinators. The parcel is divided into twelve subplots by alder trees.Eac h subplotha s 100 trees.I n the subplots there are 0, 10,2 0 or 60%Golde n Delicious trees;eac h density is replicated three times.U p till 1978onl y a small difference between thedensitie s occurred.Adde d up for the sixbearin g years 1973-1978,on e tree in the zero plots gave an average of 496.3fruits . In the subplots with increasing percentages of pollinators this sumwa s 525.0, 533.5 and 572.6 fruits per tree,respectively . Ink g per tree the effectwa s less clear (66.4, 66.7,67.9 ,an d 68.2)becaus e with increasing numbers per tree the fruits became smaller (134, 127, 127,an d 119 grespectively) .Wit h every increase inpollinato r density, the number of good and dull seeds per fruit increased weekly. Possibly, the rather small differences between the treatments are due toa mutua l influence of the subplots.

Pear On Parcel 24 of the experimental garden atWilhelminador p in the spring of 1972 trees of Doyenné duComic e onQuinc e Awer e planted. Pollinator is Conference and inon e case Durondeau aswell . The parcel is divided into twelve subplots divided by alders, each having 80 trees.I n three replicates the following pollinator densities occur: 0, 10,50 ,an d 66%.I n the latter treat­ ment half of pollinators consists of Conference,hal f of Durondeau. Summed over thebearin g years 1974-1978,th e trees yielded on average 126.2, 137.3, 152.1, and 146.6 fruitswit h increasing pollination densities.Expresse d ask g per tree the yield was 29.6,33.4 ,35.8 ,an d 34.6.Tota l number of seeds per fruit averaged for 1976 to 1978wa s remarkable constant, i.e. 9.3, 9.4, 9.3, and 9.3 respectively. However, good seeds per fruit increased (2.2,3.0 ,4.0 , and 4.4) with increasing pollination density,wherea s number of dull seeds per fruit decreased (7.1,6.4 , 5.4,an d5.0) .

19 Screening unusual fruit crops

S.J. Wertheim and J. Dijkstra

The collection of lessknow nwood y plant specieswit h useful fruitswa s con­ tinued. Some of these species have yielded their first crops,namel y theHazel , theWalnut , theElde r and theQuince . In the spring of 1974 three Hazel cultivars were planted: 'Frühe vonFrauen ­ dorf', 'Géant de Halle' and 'Webb's Price Cobb'.Fiv e to sixbushe s per culti- varwer e planted. Thebushe s began tobea r fruit in 1976.I n 1976, 1977 and 1978 'Frühe vonFrauendorf ' consistently yielded 0.17 kgpe r bush.Frui t weight in 1978 amounted to 2.61 g. 'Géant deHalle 'yielde d 0.68, 0.48, and 0.22 kg per bush,respectivel y and the 1978frui t weightwa s3.0 6 g.'Webb's Price Cobb' produced 1.13, 1.10,an d 1.28 kg perbush , respectively. Fruit weight in 1978 was 2.36 g. Also in the spring of 1974 three trees of each of the following Walnut cul­ tivarswer e planted: 'Broadview','Buccaneer ' and 'M.286'. The trees began to yield in 1977. 'Broadview' gave in 1977 and 197857. 7 and 67.3 nuts per tree (or0.6 7 and 0.83 kg per tree). Fruitweight s were 11.7 and 12.4 g. 'Buccaneer' produced 29.3 and 58.0walnut s (0.47 and 0.73 kg) and fruitweigh t was here 15.9 and 12.6 g. 'M.286' yielded 41.6 and 31.7 nuts per tree (0.47 and 0.37 kg) in these twoyears .Frui tweigh t was 11.2 and 11.6 g. Three Danish Elder cultivars were planted in the spring of 1975;a few bushes per cultivar. It concerned 'Alles^e', 'Hamburg', and 'Kors^r'. The fruits came in 1977.On ebus h of each cultivar was analysed in 1977. 'Alles^e' gave 16.9kg . Each fruit cluster had an average of 457berrie s and berry weight was 0.169 g. 'Hamburg', awea k grower,yielde d 2.0 kg and no further countings weremade . 'Kors^r' produced 9.7 kg,wit h 337berrie s per cluster and an average berry weight of 0.174 g. In 1978yiel d was higher.Th emea nyiel d of twobushe s was for 'AllesçSe'46. 7kg , for 'Hamburg' 10.5kg , and for 'Kors«Sr' 24.8kg . The diameter of thebushe s in 1978wa s 3, 1.5 and 2m , respectively; theheigh t 3, 2, and 2.5 m. 'Hamburg' is a slow grower,bot h other cultivars grow vigorously. Inbot h years itwa s necessary to cover thebushe swit h nets tokee p birds off. A new experimentwit h these and the cultivars 'Donau', 'Haschberg', and 'Sambu' will be set up. In spring 1974a few bushes of each of the following Quince cultivars (budded onHawthorn )wer e planted: 'Champion', 'Lescovacs',an d 'Reas Mammouth'. Fruit bearing started in 1976. 'Champion' produced in theyear s 1976, 1977,an d 1978 30.5, 11.0,an d 32.5 fruits perbus h (or 6.7, 1.6, and 4.9 kg).Frui t weights were 218, 146,an d 149 g. 'Lescovacs'yielde d 38.7,7.0 , and 96.7 fruits perbus h (average of three bushes) or 6.5, 0.9, and 11.6kg . Fruit weights were 168, 124,an d 120g respectively. 'Reas Mammouth' appeared rather unproductive; 5.0, 7.0,an d 5.0 fruits per bush (1.6, 1.2,an d 1.1 kg).Averag e fruit weights were 320, 171,an d 220 g. Budding onhawthor n proved disadvantageous.Man y root suckers had tob e removed. Furthermore, compatibility with 'Champion' and 'Reas Mammouth'wa s not very good.Al l quinces proved susceptible tomildew . In 1978a new experimentwa s prepared. OnQuinc e C the following cultivars were budded: 'Berecki', 'Champion', 'De Bourgeot' (or 'Borgeaut'), 'Isfahan', 'Lesovacs' (or 'Lescovacz'), 'Ludovic', 'Pear Shared', 'Reas Mammouth', 'Serbian', 'Shams'an d 'Vranja' (or 'Géant de Vranja').

20 Virus research and clonal selection in fruit trees

H.J. van Oosten

Results of trialswit h virus-free and virus-infected treeswer e similar to those of previous years.I n a six-year-old trial under very vigorous growing conditions the diameter and theheigh t of treeswer e measured (Table5) .

Table 5. Tree dimensions and ratio of yield to tree volume of 3varietie s at Numansdorp.Yea r of planting 1973.

GoldenDeliciou s Cox's O.P. Rode Boskoop

Tree diameter (m) virus-free 1.63 1.71 1.85 virus-infected 1.50 1.63 1.70 Tree volume (m3) virus-free 2.3 2.5 2.8 virus-infected 1. 8 2.1 2.5 Kg/m3 virus-free 55 29 33 virus-infected 53 34 33

The volume of thevirus-fre e treeswa s 10-20% greater than that ofvirus - infected trees.I n this trial the distance between the trees in the row is 1.41 m. This isquit e normal for standard trees in the area. The data on the diameter of the crowns of trees give information about themos t suitable dis­ tancebetwee nvirus-fre e trees.I t isknow n that slender spindles in aro wma y have an overlap of crowns of 25-50 cm (after pruning). Thus the virus-free Golden Delicious in this trial could have been planted at 1.25 m to get the optimal tree density in the row.Fo r Cox's Orange Pippin the distance of 1.41 m is acceptable but for thever y vigorous Rode Boskoop adistanc e of 1.50-1.55m seems tob ebest . It iso f interest tonot e that theyiel d efficiency, the ratio yield to tree volume (kg/m3),wa s similar forvirus-fre e and virus-infected trees of Golden Delicious and Rode Boskoop.Fo r Cox's Orange Pippin theyiel d efficiency was better forvirus-infecte d trees. In trialswit h different sources of Golden Delicious the clone 'Smoothee' was very remarkable. Fruits of this clone are much smoother than those of other clones inmos t years buth especially in 1978.Yiel d of trees of 'Smoothee'ha s been lower than that of Clone B so far.

Researcho ncultur ei nfrui t tree nurseries

H.J. van Oosten

It could be shown,a s inpreviou s years, that cutting back of budded root- stocks inJanuar y causes an earlier outgrowth ofbud s than cutting back later (April). Due to the low temperatures (no frosts,bu t untilmi d April the tempe­ raturewa s lower than 10°C), thedifference s in growth were small.I n one nursery some rootstocks were cutbac k inMay . Thebleedin g of the rootstocks

21 was severe,bu t all thebud s survived and grew out.Th e treeswere ,however , smaller. The symptom of papery bark was only observed in some rootstocks that were cutbac k already in December or January. The thickness of a rootstock planted out in anurser y may be of importance for tree quality. This year no influence of thickness of rootstock was observed with Rode Boskoop.Tree s of Cox's Orange Pippin on the thickest rootstocks were heavier feathered but no thicker or longer than those on thin rootstocks (Table 6).

Table 6. The influence of the thickness of theM. 9 rootstock on tree quality of Cox's Orange Pippin.

Thickness of rootstock (mm) Growth per tree in 1978 spring '77 spring '78 length (cm) thickness(mm ) number of feathers

5 9.7 115 12.9 1.7 7 11.6 120 13.5 2.4 9 12.5 118 13.5 3.1 11 15.8 118 13.1 5.5

Maiden trees are usually made by budding on a rootstock. Somevarieties , however,d o not feather aswell . For that reason nurseries areno w producing whips thathav ebee n grown for two seasons.Afte r one growing season thewhip s have usually made only an unfeathered shoot. Different trees are obtained by cutting back at different heights. Cutting back very deep (55 cm above the soil level)give s unsatisfactory trees of Rode Boskoop because then thene w central leader does not feather sufficiently.Wit h Jonagold and James Grieve also too many poorly feathered treeswil l occur.Wit h Rode Boskoop and Jonagold thebes t treeswer e obtained by cutting back at 90 cm,becaus e of thebeautifu l side twigs on the stem.Mor e and slightly weaker featherwil l occurwhe n trees are cutbac k at 120cm . For James Grieve thebes t treeswer e obtained when trees were cutbac k at 75 cm.

Selection in rootstock clones

Inth enurser yman ysource s of virus-free M.9hav ebee ncompared .Tw o selections seemed tob e quite different: aGerma n no. 1an d aBelgia n no. 29.Th e German no. 1ha s abeautifu l arrangement of leaves: large,dar k green shine leaves. The shoots are mainly without spines.Th e Belgianno . 29,o n the contrary,ha s much smaller,dul l leaves and ismuc hmor e like thewell-know n standard (virus- infected)M. 9 (Jaune de Metz). It is,however , remarkable that this clone (no. 29)ha s many spines on the shoots.Anothe r difference is the leaf serrations: the leaves of the German clone are obtusely serrate,wherea s those of the Belgian clone are acutely serrate. In some other clones both types of leaf serrations were seen ondifferen t layers.Th e importance of the differences will be studied.

22 Rootstocks and interstocks for pit and stone fruits H.J.va nOoste n

Apple

Rootstocktrial s includingth ewea kM.2 7hav ebee nplante d insevera l experimentalgarden swit hdifferen tgrowin gconditions :a wea kgrowt ha tWilhel ­ minadorpan da vigorou s growtha tNumansdor pan dKraggenburg .Som eresult sob ­ taineds ofa rar esummarize di nTabl e7 .

Table7 .Tre edimension s (1978)an daccumulate dyiel do ftree so nM. 9an dM.2 7 ondifferen tsites .

Variety/rootstock Tree kg/tree kg/m3 (site) ,. ,. . ., ,N diameter (m) height (m) RodeBoskoo p (Wil.) M.9 1.54 1.92 38.5 32 6 M.27 1.03 1.61 21.1 44 .9 RodeBoskoo p (Kr.) M.9 1.61 2.48 3.1 1. 8 M.27 1.10 1.77 4.6 7 .3 RodeBoskoo p (Nu.) M.9 1.56 2.45 25.5 16 .0 M.27 0.95 1.75 15.7 36 .5 Wil.:Wilhelminadorp ,tree splante d in1974 . Kr. :Kraggenburg ,tree splante d in1976 . Nu. :Numansdorp ,tree splante d in1976 .

AtNumansdor pan dKraggenbur g thegrowt ho fvirus-fre e treeso nM. 9i sver y vigorous.Growt ho ftree so nM.2 7i smuc hweake r andthi si sconsidere d tob e ofmuc hinterest .A tWilhelminador pgrowt ho ftree so nM. 9i smoderat ean do n M.27to oweak .Th erati oo fyiel d totre evolum e (kg/m) i smuc hbette rfo r M.27i nal ltrial s (Figures 1an d2 ,pag e 24).Th emea nfrui tweigh ti sth e lowestfo rfruit so ftree so nM.27 .Thi si sn oproble mfo rth elarge-size dappl e Schoneva nBoskoo pbu ti tma yb ea proble mfo rCox' sOrang ePippi nan dWinsto n whichusuall yhav esmal lt omediu msize dapples .Crackin go ffruit so fKarmij nd e Sonnavillewa smor esever eo nM.2 7an d theeve nweake rrootstoc k342 6tha no nM.9 . TheRussia nB. 9 ismor evigorou stha nM.9 .Th erati oo fyiel d totre evolum e (kg/m3)i sfo rCox' sOrang ePippi nequa lfo rbot hrootstocks .Wit hRod eBoskoo p therati oi smuc hbette rfo rtree so nM.9 . Therootstoc kM.2 6i smor evigorou stha nM. 9bu ti nth ewea kgrowin gcon ­ ditionso fWilhelminador p thisshoul dno tb ea problem .However ,th erati oo f yield totre evolum ei smuc hbette ro nM. 9i nth efirs t5 year safte rplanting . Inth etria lwit hC.G .rootstock sonl yC.G . 10an dC.G .6 0induc ea weake r growththa nM.9 . Theeffec to fa rootstoc kca nb eincrease db yincreasin g itslength .Thi s happenswhe nrootstock sar ebudde dhighe rtha nnormal .I ti sshow ntha tth e yield andgrowt ho ftree si sinfluence db y theheigh to fbuddin g (Table8 , seepag e25) . Inarea swher egrowt ho nvirus-fre eM. 9 isconsidere d toovigo ­ rous,i tmigh tb eusefu lt ous erootstoc kpart slonge rtha nnorma l toobtai n weakergrowth .

23 ••'ig. 1.Re dBoskoo po nM. 9 (v.v.)i n thefift hgrowin gseaso na t Wilhelminadorp.

Fig.2 .Re dBoskoo po nM.2 7 (v.v.)i n thefift hgrowin gseaso na t Wilhelminadorp.

24 Table 8. Influence of the height of budding on growth and yield of Rode Boskoop at Numansdorp.

Height of budding (cm) Tree volume 1978 (m3) kg/tree 1972-1978 kg/m3

10 2.4 96 41 20 1.9 92 48 30 1.7 91 55

Pear

In trials with Quince A and Quince C thehighes t yields were obtained of trees on Quince C.

Plum

Victoria on Prunus pumila showed serious symptoms of incompatibility in 1978. Identical symptoms,bu t to a lower degree were also seen in some younger trees on P. besseyi. In the nursery ten plum varieties were budded on to P. pumila. Most varieties showed symptoms of incimpatibility but Ontaria and Warwickshire Drooper gave a good bud take and developed excellently in the nursery.

Fruit variety trials

P.D. Goddrie

Apple

In the 1977/78 planting season 55 new varieties were set out for the first screening trials atWilhelminadorp . In general,flowerin g and fruit setwer e very abundant so thatnearl y all varieties had tob e thinned heavily. The quality of the fruits,however ,wa s severely reduced by a shortheav y hail storm on 23 June. In contrast to previous years damage of the fruits by birdswa s rather low in 1978.Onl y a few early-ripening varieties had tob e protected by nets. Againvisitor s to the variety plots showed a great deal of interest for Akane, Elstar, Summerred,Jonagold , and Gloster 69. The enthusiasm of commercial fruit growers for Elstar diminished in 1978, because of the great percentage ofbad-coloure d or even uncoloured fruits.Th e production of Elstar is annually good,whil e its flavour is appreciated by almost everyone. Till now Gloster seems tob e a red-coloured long-keeping variety with an excellent production. In taste experiments thisvariet y mostly scores low. Also the production of Jonagold is good,whil e its flavour is appreciated generally.Howeve r this variety isno t really ared-coloure d keeping variety. Especially in 1978 the fruit colourwa s very disappointing, even at the late picking at the end of October. Summerred showed very clearly its tendency tobiennua l bearing. After a too heavy crop of 22.2k g per tree in 1977,onl y apoo r one of 10.5k g per treewa s achieved in 1978. Fruit colour of this variety isver y bright on the tree

25 shortly before picking;onc e the fruits are picked their dull-green back sides become visible so that they are not so attractive when packed in acrate . Smoothee, anAmerica n mutation of Golden Delicious is receiving much interest because of its smooth fruit skin.Wit h respect to fruit shape, flavour,an d storage,n o clear differences were noticed between Smoothee and standard Golden Delicious. Taste experiments,carrie d out in December 1977,th e results ofwhic h were given in the 1977Annua l Report,wer e continued in January andMarc h 1978.Als o in 1978 thevarietie s Elstar,Karmij n de Sonnaville, and Jonagold had thebes t flavour. In a taste experiment early inNovembe r thevarietie s Akane,Jamb a 69, Summerred, and Cox's Orange Pippinwer e compared. There were no significant differences in the scores of Jamba 69,Cox' s Orange Pippin, and Summerred, 6.2, 6.1, and 6.0 respectively. Akane,however ,wa s significantly poorer in taste with a score of 5.0 (1= very bad taste; 10= excellent taste). On thebasi s of the results obtained in the last fewyears ,eleve n varieties were grubbed at the end of 1978.

Pear

In the spring of 1978 threene w varieties were planted in the first screening trials. In general, flowering and fruit set of the pear varieties were good.Especial ­ lywit h cooking varieties good yields were obtained (Table9) .

Table 9. The averageyiel d per tree in the 1973-1978 period, obtained from four cooking pear varieties on Quince Awit h interstock Beurré Hardy, planted in the spring of 1972.

Variety kg per tree

Saint Rémy 81.1 Gieser Wildeman 49.2 Winterrietpeer 45.2 Witte Kozijn 37.6

Of the varieties under trial,eigh t are from the IVTpea rbreedin g programme. Although the trees of these selections are rather young, it could be seen that evenwit h pears yields canb e obtained already in the second growing season. The results obtained with anumbe r ofmutation s of Beurré Hardy, Conference,an d Doyenné du Comicewer e again disappointing, aswa s the casewit h other mutations in previous years. At theen d of 1978si xvarietie s were grubbed on thebasi s of the results obtained in the last fewyears .

Plum

In the spring of 1978 the variety Eddawa s planted in the first screening trials. Both flowering and fruit setwer e excellent, so that yieldswer e high in 1978. The variety Sanctus Hubertus forms quite a small tree on St.Julie n A, producing a regular crop almost every year. Itseem s tob e avariet y that can be recommended to the fruit growers.Th e taste of this variety,however ,i s only moderate.

26 Second screening trials in experimental orchards

The apple trial 71.0.3.,plante d onM. 9 in

Table 10.Th e averageyiel d ink g per tree,obtaine d from five apple varieties onM. 9 in four experimental orchards in the 1972-1978 period. Trial planted in the spring of 1971.

Variety Experimental orchard Average of Gelder- Kraggen- Numans- Oost- four orchards malsen burg dorp * huizen

Karmijn de Sonnaville 37.4 75.5 66.4 -* * 59.8 *** Cox's Orange Pippin 47.3 74.5 64.3 68.6 63.7 Oranje de Sonnaville 55.1 76.3 59.8 63.9 63.8 Holstein 66.4 102.1 96.1 89.7 88.6 Alkmene 73.0 85.1 83.3 70.7 78.0

* yields 1973-1978. ** many trees killed by rats. *** average of three orchards.

Holstein and Oranje de Sonnavillewer e not the desired improvements on the varieties grown inpractice ,bu t they are notba d varieties.Alkmen e gave the lowest yields,bu t the trees of thisvariet y remain rather small onM.9 .A s thisvariet y is picked in thebeginnin g of September it could possibly fill the gap between James Grieve and Cox's Orange Pippin. Also the apple trial 73.0.1.,plante d onM. 9 in the spring of 1973,wa s ended after the 1978 growing season. As is shown inTabl e 11, also in this trial Karmijn de Sonnaville gave the highest yields.

Table 11. The average yield ink g per tree,obtaine d from ten apple varieties onM. 9 in five experimental orchards in the 1974-1978 period. Trial planted in the spring of 1973.

Variety Experimental orchard Average of five Gelder- Kraggen- Numans- Oost- Horst orchards malsen burg dorp huizen

Karmijn de Sonnaville 66.5 63.5 52.7 73.0 79.6 67.1 Elstar 34.0 24.7 31.6 43.8 33.8 33.6 IVT 5544-220 36.9 46.6 39.0 54.4 34.6 42.3 Cox's O.P. T6 1 43.3 55.0 50.6 62.4 24.2 47.1 IVT 5529-129 69.0 61.3 63.2 88.4 66.6 69.7 Cox's O.P. 81.6 68.7 88.4 90.9 83.3 82.6 IVT 5529-46 54.1 48.5 58.0 77.5 54.3 58.5 Winstar 41.9 40.3 46.2 49.2 36.8 42.9 Alofs' Cox Spur 37.9 - 39.0 34.2 43.5 38.8 * IVT 5442-17 42.1 31.9 41.9 40.2 53.0 41.8

* average of four orchards.

27 Thevirus-fre e Cox's Orange Pippin T 61 has tob e preferred over Cox's Orange Pippin and Alofs' Cox Spurbot h not tested forvirus .Alofs ' Cox Spur does not have a real spur type character. IVT 5544-220 isa variet ywhic h canb e stored for a long period; its appearance resembles that of Elstar,whic h has amuc h better eating quality. The other three IVTvarietie s under number are summervarietie swit h a moderate productivity and short shelf-life;frui t cracking hasbee n observed ina number ofyears . Winstar, amutatio n ofWinsto nwit h bigger fruits,doe s not appear tob e an improvement of the standard Winston. The percentage bigger fruits of Winstar was not higher than that of standard Winston. After four growing seasons of apple trial 75.0.13.,plante d onM. 9 in the spring of 1975,Jonagol d gives thehighes t yieldswit h 34.4 kg per tree, followed by Gloster and Golden Deliciouswit h 31.9 and 30.7 kg per tree,res ­ pectively. Jamba 69,Septer ,an d James Grieve produced 21.2, 17.4,an d 15.4k g per tree, respectively. A new trialwit h tenpea r varieties and onewit h ten sour cherry varieties arebein g prepared.

28 SMALL FRUIT SECTIC

Culture experiments with strawberries

J.Dijkstr a andA.A .va nOoste n

Irrigation in plastic tunnels

As in197 7som e irrigation systems insmal l plastic tunnelswer e compared. Under investigationwer e thebi-wal l system, theviaflo w systeman da syste m with bigger tubes anda muc h greaterwate r supply peruni t oftime . Three varieties were planted atth ebeginnin g ofAugus t 1977i na blac k plastic soil cover.Durin g thefirs tweek s after planting allplant swer e irri­ gatedwit h asprinkle r system. Although thegrowin g seasonwa sno tver y dry,irrigatio nwa snecessar yfo r longperiod s inautum n 1977a swel l asdurin g thesprin go f1978 . Duet opartia l blockage,a tth een do fth egrowin g season,th eamoun t ofwate r supplied with thebi-wal l systemwa sslightl y reduced.Wit h theviaflo w system decreasei n water supplywa smuc hbigge r andthi s probablyha da negativ e effecto nth e production. As Table 12show s irrigation resulted inhighe r yields anda bette r fruit size (asi n 1977).

Table 12.Tria lwit h three systemso fwate r supply

System kg/m2 Percentage Average fruit Mean harvest 1stqualit y weight (g) date

Control 1.42a 73 9.4 7.06 tubes 1.83b 78 10.9 8.06 Bi-wall 1.73b 77 10.8 7.06 Viaflow 1.66b 77 10.0 7.06

Comparison of some Gorella 'clones'

Aimo fthi s trialwa st oinvestigat e whether there areclona l differencesi n strawberries andals o tocompar e runner plants from tissue-culture plants with those ofnormall y propagated motherplants . Plants ofGorell awer e obtained from Hiree propagation fields.I nDecembe r 1976, some plants ofeac ho fthes e 'clones'wer e sentb yD rBoxu s ofth e Research Stationfo rFrui t andVegetabl e Growinga tGembloux ,Belgium .H emad e meristems andpropagate d theplant sb ytissue-culture .I nMarc h 1977,a propa ­ gationfiel dwa splante d with virus-free,normall y grownmothe r plants ofth e three 'clones'.O nJ Jun e tissue-culture mother plants were setfro mth esam e 'clones'a swel l asfro mtw oBelgia n 'clones'.A productio n trialwa splante d on ]2Augus t J977wit h 16replicates .Th eresult s aregive n inTabl e13 .

29 Table 13. 'Clones' of Gorella

Origin Judgment G/plant Percen­ Average fruit October tage 1st weight (g) 1977 * qual Lty

1.Belgi ë 1, tissue-culture 5.2 552 a 68 13.4a

2. België 2, ii ii 6.7 662b c 77 16.8b 3.Nederl.l , normal 7.6 673b c 76 15.4b

4. Neder1.2, H 7.5 611 b 77 16.7b 5. Neder1.3, H 7.6 652b c 76 16.2b 6.Nederl.l , tissue-culture 6.7 633b c 78 16.3b 7. Neder1.2, H H 6.4 619b c 79 16.6b 8. Neder1.3, H M 7.2 695 c 75 15.5b

* 1= ba d growth; 10= very good growth.

'Clone' Belgium 1ha d a lower production and less first quality plants than all other clones.Alread y in autumn 1977 it could be seen that growth of this clone wasmoderate . It is not clearwhethe r this is caused by real clonal differences orwhethe r the time duringwhic h plants were propagated in-vitro also had an effect. Therewer e no significant differences between the three Dutch clones nor between plants obtained fromnormall y grown plants or from tissue-culture plants. Strikingwa s that aviru s test in spring 1978 (oneyea r after plantingvirus - free plants in the open) showed that in nearly all treatments already a certain percentage of the plantswer e infected with virus (mild yellow edge and mottle), inspit e of a low infection pressure. The trialwil l be repeated next year.

Variety testingo fstrawberrie s

J. Dijkstra,J . Blommers,an d A.A.va n Oosten

Plastic tunnels

In the irrigation trial in small plastic tunnels thevarietie s Karina, Elvira and Gorellawer e compared. Planting was rather late:4 Augus t for Elvira and 9Augus t forKarin a and Gorella.Th e plantswer e set in ablac k plastic soil cover,whic hwa s unsatisfactory under the given conditions:a cla y soilwit h too many clods.Rootin g was difficult and many plants finally stood too deep.O n clay soils it seems better toplan t first and tola y the plastic soil cover later in autumn. The results (Table 14)ar e confirm those obtained in 1977.

Table 14.Variet y testing of strawberry under plastic cover.

Variety kg/m2 Percentage Average fruit Mean harvest 1st quality weight (g) date

Karina 0.87 78 9.1 1.06 Gorella 1.69 79 11.3 10.06 Elvira 2.39 73 10.4 11.06

30 Again Karinawa sb y farth eearlies t ripening variety, butyiel d was lowan d berries were rather small. Forhighe r yield Karina hast ob e planted early. Gorella andElvir a ripen at thesam e time,bu tproductio n of Elvira was clearly higher. Fruits of this variety taste good. For growing under Dutch lights as well as forunde r plastic tunnels Elvira isa good variety.

Variety trial in the open

In this trial 8 selections of IVT (Institute forHorticultura l Plant Breeding) were compared with thestandar d varieties Gorella, Sivetta, Tago and Tenira at theIVT ,th eexperimenta l gardens inBred a andHorst , the demonstra­ tion farm forsof t fruits inKestere n anda t theResearc h Station. Three selec­ tions were rejected, three will be tested again in 1979.Tw oselection s con­ firmed thegoo d impression they made in previous years andwer e introduced by the IVTa s Korona andBogota . Korona is a mid-season variety with very attractive, good tasting fruits. Bogota isa very late variety that ripens even some days later than thelat e variety Tago. Both newvarietie s areproductive . On theResearc h Station also some foreign varieties were tested. Of these Sequoia was early ripening with fruits of good flavour, unfortunately produc­ tivity was low.Belrub i ripens mid season with a good production of long conical fruits. Cambridge Favorite again wasth emos t productive variety; fruits are, however, toopal e andrathe r small.

Cold-stored waiting field plants (for a late harvest)

In recent years there hasbee n increasing interest in lengthening the harvest season. This canb e achieved by growing everbearing varieties but also by growing cold-stored waiting field plants. Choice of varieties is,however , very limited. Only Redgauntlet and Sivetta give good results with planting dates up to July. For this trial, laid outo n four places, the following varieties and selections were chosen: Redgauntlet, Sivetta, Gorella, Korona, Tago, Tamella, Tenira, IVT 72138 and IVT 72343.Al l runner plants came from one propagation field, were planted onon ewaitin g field in Breda and afterwards stored at -2°C. The production fields were planted on 20Ma y1978 . The results are summarized in Table15 .

Table 15. National strawberry variety trial with cold-stored waiting field plants.

Yield (1stan d 2nd quai ity) Mean Percen­ Percentage in percentages yield tage2n d fruitrot (kg/m2) quality Breda Horst Keste re nW 'do rp

Sivetta 100 100 100 100 2.10 b 12.4 a 5.1 a (kg/m2) (188) (243) (171) (239) Redgauntlet 89 93 104 96 2.01 b 14.8 a 4.1 a Gorella 96 84 91 65 1.74 a 19.8b 3.2 a Tago 89 93 121 92 2.05 b 12.9 a 5.5 a Tamella 99 74 125 96 2.02 b 20.6 b 14.3 c Tenira 84 106 105 90 2.03 b 19.8b 3.5 a IVT 72138 103 79 132 87 2.05 b 21.9 b 9.4 b Korona 95 86 94 69 1.79 a 25.8 c 4.3 a IVT 72343 107 96 119 97 2.18 b 11.2 a 5.5 a

* Average forBreda , Horst and Wilhelminadorp.

31 There proved tob eman y interactions between varieties and sites.I twas , however, impossible to find agoo d explanation for them. On the average Gorella and Koronawer e the least productive,an d had ahig h percentage of second quality fruit asha d Tamella.Tamell a alsowa s very susceptible to fruit rot. On all places Sivetta and Redgauntlet gave thebes t results.Whe n there were other varieties as productive or evenmor e productive,qualit ywa s always poorer (fruit shape and colour). Therefore Sivetta and Redgauntlet still are the recommended varieties for culture with cold-stored waiting field plants.

Everbearing varieties

As a continuation of thevariet y trial in 1977agai n at several places some new IVT-selectionswer e compared with Ostara.Agai n it turned out tob e diffi­ cult to find avariet y thatbeat s Ostara. Selections IVT 73119 and 73128wer e held for further trial.Th e English variety Aromel had big fruits that taste very good,bu t unfortunately production againwa s too low. A preliminary study of the French varieties Bordurella and Tapirellawa s disappointing. Both varieties had a low production.Fruit s of Bordurella were too small and those of Tapirellawer e misshapen.

Culture experiments with raspberriesan dcurrant s

J. Dijkstra and A.A.va n Oosten

Raspberry

In the experimentwit h drip irrigation for raspberries,productio n inal l treatments was about the same in spite of important differences in growth in 1977 (Table16) .

Table 16.Dri p irrigation with the raspberry variety Schönemann

Length of tied Kg/m2 shoots cm/m row spring spring 1977 1978 1977 1978 Total

control 210 850 0.52 2.04 2.56 one side (throughout season) 390 1120 0.99 2.06 3.05 two sides (throughout season) 470 1220 1.02 2.04 3.06 two sides (from 1.06)* 460 1120 0.99 2.23 3.22 two sides (from 1.07)* 380 1240 0.89 2.18 3.07

* in 1976 from 1.08.

It seems that under the conditions of 1978plan t density in the untreated con­ trolwa s already optimal.Th e effect of more growthwit h drip irrigation was also reduced by pruning all treatments at the sameheight . Furthermore much rain just before the ripening period probably accounts for the lack of diffe­ rence infruitsize . In autumn therewa s a tendency that themor e water that

32 was given the lower the percentages of minerals in the leaves. Some shoots even had yellow tops. Yield of Glen Clova and Mailing Promise grown in theNe w Zealand horizontal training systemwer e lower than yields of the samevarietie s grown as ahedge .

Red-ouvrants

With the red currantvariet y Jonkheer van Tets drip irrigation gave 25 to 40% more pruned wood in thewinte r 1977/1978 and yieldswer e againhighe r than those of the untreated control.Ther ewa s also a tendency for irrigation to result in ahighe r berryweight .

Black-currants

Twomino r experiments with cuttings were continued. In the one started in spring 1975,remova l of theblac k plastic soil cover gaven o difference in pro­ duction compared with the still covered treatment. In the trial started in the spring of 1976 planting of cuttings in the black plastic soil coverwa s compared with an untreated control and led tomor e production in 1977 and 1978.Makin g holes in the plastic after the first growing season gave 50%mor e pruning weight,bu t production was nothigher .

Variety testingo fraspberries ,currant san dblackberrie s

J. Dijkstra and A.A.va n Oosten

Raspberry

Again in 1978viru s free plants ofMailin g Jewel,Mailin g Promise,Rod e Radboud, Lloyd George and Sirius gave excellent fruits. Strikingwer e thehig h yield ofMailin g Promise and the good quality of Rode Radboud. The raspberry variety trial gave a first yield. Only Mailing Admiral, Mailing Orion (planted spring 1978)an d Leo (notye t planted) are not included. After the first harvest the following characteristics of the varieties canb e given (inorde r of ripening time): Glen Clova,growt h strong,productivel y good,berrie s somewhat hidenb y the leaves, somewhat light coloured, firm andwit h a good taste. Mailing Promise,growt h and productivity good,berrie s of agoo d size,bu t relatively soft and susceptible to fruit rot. Delight, growth good, this first year very productive with very bigberries , light coloured, softwit h a good taste. Spica, growth and production good, firm but smallberries . Glen Isla,goo d growth,berrie s round,rathe r smallbu tver y firmwit h a good colour. Jochems Roem, growth and yield disappointing,berrie s big,dar k and rather soft. Tastemoderate . Phyllis King,growt h very strong,productio n good,berrie s rather big,dar k red, pretty firm andwit h a good taste.Mea nharves t date in 1978 one week later than Glen Clova. Himbostar, growthmoderate ,productio n good,berrie s firmbu t small. Schönemann, good growth and production,berrie s dark coloured, rather small and firm.

33 In the spring of 1977a trialwit h autumnbearin g raspberry varieties was planted. In 1978 theyiel d of varieties September and Scepterwa s low (0.3kg / m2) and fruitswer e too small.Productio n of Heritage was good (0.8 kg/m2). Theberrie s were small but firm and of a good colour. Ripeningwa s relatively early. Barond eWavr e is the strongest grower in thisexperiment .Yiel d was good (0.7kg/m 2)bu t it ripened late,a disadvantag e in cold,we t autums. The berrieswer e rather big, reasonably firm andwit h a good taste and colour. Zeva Herbsternte also gave agoo d production (0.7kg/m 2). This variety is early ripeningwit h reasonable big fruits of a dark colour and good taste.

Red-currant

The results of thevariet y trial are given inTabl e 17 as are the results of thebes t varieties and selections in the preliminary trial.

Table 17. Results of red-currant variety trials (averages 1976/1978).

Variety Kg/m2 Average Berries/ Date berry string full bloom harvest weight (g)

Jonkheer van Tets 1.53 0.82 7.0 29.04 7.07 Stanza 1.57 0.71 9.8 6.05 16.07 Rotet 1.36 0.87 12.1 25.05 24.07 Rondom 1.44 0.74 11.5 3.05 27.07 B 21 1.83 0.77 12.8 5.05 29.07 Rosetta 1.77 0.92 13.8 8.05 29.07 Red Lake 2.07 0.75 9.4 1.05 13.07 IVT 69012 2.67 0.89 9.8 6.05 17.07 IVT 69011 2.21 0.72 10.5 1.05 20.07 IVT 681 1 2.33 1.00 13.7 7.05 27.07

Of the newer varieties B.21 gave good resultswit h long strings andberrie s of a good size and taste.String s of Rosetta are very long,bu t berries are pale with only amoderat e taste.Afte r two disappointing years Rotet gave a good yield,wit h berries of good taste and colour. IVT 69011 and 69012wer e high yielding,bu t susceptible to fruit rot.Th e most promising selection is IVT 6811. This selectionha s a good production with big and nicely coloured fruits that canb e picked very late.

Black-ourrant

Both vari ety trials gavehig h yields (Tables 18an d 19,se e page 35).I n the first aswe l 1 as in thesecon d trialTena h and Tsema gave thehighes t yields, Both varieti es growver y vigorously with rather flaggy shoots.Thes e canb e a disadvantage formechanica l harvesting. The standard variety Baldwin gave good results inb oth trials,Wellingto n XXX,however ,wa s disappointing in the first trial. The IVTs elections 6832 and 69002 are very late flowering,whic h diminishes the risk of damageb y night frost.Bot h selections gave good yields with big berries. In the se cond trial also Black Reward, Slitsa,Westr a and Silgo gave good results.Pr o duction of Jetwa s abi t disappointing. Strings of Jet are very

34 longbu t berries are small. At the Spenger Institute processing qualitieswer e investigated in 1976/77 aswel l as in 1977/78.I n 1976/77 Black Down gave thebes t results, theM-5 9 numbers and Baldwinwer ewel l appreciated,Wellingto n XXXha d the poorest flavour. In 1977/78Baldwin , Black Reward, Jet and four IVT selections were judged. Jet and IVT 69010 gave thebes t results.

Table 18.Result s black-currant variety Trial 1(average s 1976/78).

Kg/m2 Average Berries/ Date berry- 1978 1976/78 string Fullbloo m Harvest weight(g )

Baldwin 1.42 0.89 1.07 5.4 03.05 23.07 Wellington XXX 1.31 0.67 1.19 4.5 03.05 18.07 M 59-3 1.40 0.87 1.06 5.2 05.05 21.07 M 59-4 (Tenah) 1.59 1.06 1.16 6.9 03.05 17.07 M 59-8 (Slitsa) 1.46 0.78 1.04 5.0 30.04 18.07 M 59-10 (Tsema) 1.58 1.07 1.06 6.1 30.04 18.07 IVT681 3 0.95 0.66 0.86 6.3 03.05 24.07 IVT 6832 1.43 0.98 1.18 5.6 13.05 21.07 IVT 69002 0.96 0.91 1.23 5.2 14.05 25.07 IVT6901 0 1.31 0.85 0.96 5.4 06.05 21.07 Risager 1.30 0.80 0.94 4.9 27.04 14.07 Magnus 0.80 0.44 0.85 4.8 01.05 15.07 Ben Nevis 1.02 0.67 1.20 3.9 02.05 15.07 Ben Lomond 0.88 0.56 1.07 4.4 03.05 15.07 Black Down 1.42 0.77 1.02 5.2 02.05 18.07

Table 19.Result s black-currant variety Trial 2.

Kg/100IT 2 Average Berries/ Date — berry- string 1977 1978 Fullbloo m Harvest weight(g )

Baldwin 18 128 0.84 4.6 02.05 23.07 Wellington XXX 5 135 1.04 4.2 02.05 21.07 Black Reward 28 116 1.0 8 5.0 07.05 22.07 Tenah (M 59- 4) 10 146 0.98 7.0 29.04 17.07 Slitsa (M5 9 -8) 15 124 1.04 5.9 27.04 17.07 Tsema (M59 - 10) 26 138 1.06 7.3 30.04 16.07 Jet 37 83 0.74 9.4 07.05 13.08 Strato 4 68 1.43 2.9 26.04 17.07 Meitgo 19 66 0.84 4.6 05.05 17.07 Silgo 30 106 1.14 4.1 04.05 17.07 Invigo 29 66 0.64 7.1 05.05 17.07 Wassi l 7 97 1.07 4.5 06.05 16.07 Lissil 6 96 1.15 4.3 05.05 16.07 Stripta 14 52 1.21 3.9 27.04 17.07 Westra 9 11 8 0.86 4.3 02.05 22.07

35 Gooseberry

The IVT selections 72001 and 72002 arebein g compared withWhinham' s Industry and Achilles.Bot h selections seem at least as productive asWhinham' s Industry. Production of Achilles was lower. Fruits of IVT 72001 are round, yellow and taste good. IVT 72002ha s berries of an attractive bright-red and a good taste.Th eberrie s are bigger and have a better colour than those ofWhinham' s Industry. Growth is comparable with that ofAchilles .

Blackberry

Thevarietie s Darrow, Ranger and Ravenwer e no longerharvested . These varieties are not suitable for Dutch conditions.Thornfre e gave good results with aregula r production ofbi gberrie s (Table20) .

Table 20.Blackberr y variety trial,plante d in 1975.

Kg/100 m2 1976/78 1976 1977 1978 Average Mean fruit harvest weight date

Himalaya 82 303 288 2.7 26.08 Thornless Evergreen 35 285 150 3.0 08.09 Thornfree 99 233 154 4.3 13.09 Smoothstem 248 199 202 4.8 13.09

Himalaya gave high yields but theberrie s were small.Productio n aswel l as berry size of Thornless Evergreenwer e disappointing. In the trial planted in spring 1976, the standard varieties Himalaya and Thornless Evergreen aswel l as Bedford Giant and Black Satin gave good results (Table21) .

Table 21.Blackberr y variety trial,plante d in 1976.

Kg/100 m2 Average fruit Meanharves t weight date 1977 1978 (g) 1977 1978 1977 1978

Himalaya (v.v.) 174 307 3.4 2.8 05.08 01.09 Thornless Ever­ green (v.v.) 169 128 3.4 3.2 08.09 10.09 Bedford Giant 189 337 4.3 3.9 22.08 25.08 Derksen Thornless 35 88 4.4 3.9 13.09 09.08 Black Satin 163 292 5.1 5.1 11.09 06.09 Cherokee 16 11 4.6 4.9 07.08 08.08 Comanche 13 14 5.8 5.8 10.08 16.08

Bedford Giant is an early ripening variety with manybu t small thorns. It is easier to tie its shoots than those of Himalaya.Th eberrie s are round with a dull colour and dark reddish shine. In 1978 the late ripening berries were difficult to pick and soft. Black Satin is a productive variety without thorns and with a long picking

36 period. Berries are very big, oblong, and sometimes somewhat irregular. They are shiny black with a reasonably good flavour.A s the fruits are soft and very fast ripening, thisvariet y must be picked twice aweek . Cherokee and Comanche arever y alike Ranger and Raven: erect growing with many big thorns and a low production. Ina comparison of standard and virus-free plants,yiel d of virus-free Himalayawa s twice that of the standard (with much mosaic). With Thornless Evergreen therewer e no significant differences. Virus-free plants of Thornfree and Smoothstem gave good yields of a good quality. Virus-free Smoothstem has greener and more shiny leafs than the standard. Therewer e no differences in fruit size and form.

37 SOIL FERTILITY SECTION

P.Delve r

Soil management experiments

As in former years,frui t size of Beauty of Boskoop apples in the plant den­ sity experiment inWilhelminador p was affected by the plant system and by the width of theweed-fre e tree strips.I n this experiment five nitrogen dressings are applied ina be d systemwit h 3330 trees on 0.9 ha and in three singel-row systemswit h 2930, I860 or 1130 trees on0. 9 ha. In the single-rows grass strips are combined with wide or narrow tree strips.Th e treeswer e planted in 1972. For further details seeAnnua l Report for 1977,p . 34.Th e soil isa shallow-rooted 'plaat'-soil consisting of clay overlying sand, and in the summer thewater-tabl e drops tobelo w 150 cm. Therefore the experimental results havebee n affected by drought to agreate r or lesser degree every year since the start of theexperimen t in 1972.I n 1978 the average fruitweigh t was 172g in thebed s and 171,18 6 and 193g in the single-rows withwid e herbicide strips. In the rowswit h narrow tree strips the amountswer e 194, 196 and 207 g. The data suggest that trees are less susceptible todrough t whenwidel y planted and innarro w tree strips.Th e latter iscontrar y to expectation because wider grass alleys exertmor e competion for moisture. In the narrow herbicide strips, however, the treeswer e somewhat smaller and produced less fruits compared with trees inwid e strips.Consequentl y here more moisture per tree and per fruit was available than in thewid e strips. An important consequence of drought inmos t of the years since 1972ha s been therestricte d vegetative growth resulting in a failure ofwidel y planted trees to fill up the space in the rows. This has led toa lasting lower productivity perh a in thewid e planting compared with denser plantings (see Table22) .

Table 22.Productio n per tree and perh a of Beauty of Boskoop apples in the plant density experiment.

Plant distance Herbicide Yield 1978 (cm) strips kg per tree 1000k g per 0.9 ha bed 13.1 43.6 300 x 102 wide 15.1 44.2 355 x 136 wide 18.6 34.6 395 x 205 wide 23.6 26.2 300x 102 narrow 13.8 40.4 355 x 136 narrow 17.5 32.6 395 x 205 narrow 20.5 22.8

In the same experiment afavourabl e effect of deeper penetration of roots on fruit sizewa s observed.Wher e drain ditches, 120 cmdeep , cross the tree rows, the roots penetrate toa depth of some 120 cm into themixe d soilwher e they can profit from grounwater in the capillary zone.Th e effect of thisbette r moisture

38 supplywa s assessed in the exceptionally dry year 1976 and once again in 1978, by measurement of fruit diameters just prior to picking. Compared with trees elsewhere in theplanting , trees on the said crossings had 38%an d9 %bigge r fruitvolume s in 1976 and 1978,respectively . Tensiometers readings in this experimental field have shown that ata depth of 25 cm the soil issystematicall y dier east of the trees compared with the west side.Also ,betwee n the trees the soil at this depth isdrie r inth ebed s and in the 300 x 102single-row s than in the soil of themor ewidel y planted trees. In thene w experiment on trickle irrigation, planted in 1975,fou r soil management systems are applied: grass stripswit h herbicide treatment on the tree stripswithou t tillage,combine d with mulching themow n grass either on the tree strips or on the grass alleys (CCan d CM);o r mechanical weed control with the same twomulchin g methods (MC and MM).I n 1978 the treatments affected theK percentages in the leavesbu t till now not theyiel d (virus-free Cox's Orange Pippin andSchon e van Boskoop apples). In 1975,planting-hol e treatments were carried out on guard trees of this experiment.Virus-fre e Jonathan onM. 9 showed an 18%yiel d increase in 1978 when 10t o 20 1o f garden peatwa s added to theplanting-holes ,bu t this effect was eliminated when fertilizer was added to thepeat .Additio n of garden peat resulted in a 21%highe r yield ofvirus-fre e Karmijn de Sonnaville apples only when strong root pruningwa s applied aswell ; trees planted with all their roots intact showed almost no response togarde n peat.Dippin g of intact tree roots in carbon powder prior toplantin g resulted in a 9%highe r yield in 1978. But no effect of dippingwa s observed when the rootswer e first strongly pruned. In anexperimen twit h Winston apples onM. 9 in 1-mwid e herbicide strips, large nitrogen dressings inFebruar y were compared with the same dressings spread over the growing season. The first treatment promoted grass growth on the grass alleys to such anextent , that the extramoistur ewithdrawa l inth e spring was detrimental to the trees.I n the spring four to five years after planting (1972) therewer e several dry periods,an d extra competitionb y the enhanced grass growth resulted indecrease d growth and productivity of the trees inth e early-fertilized plots. In Oosthuizen the soil management experiment was terminated. Since 1967 four treatments, chemical ormechanica l weed control,combine d with mulching of mown grass either on the tree strips or on the grass alleys,hav ebee n compared. In the finalyea r 1978 the average productions of Cox's Orange Pippin apples for the treatments CC,CM ,M C and MMwer e 40.07, 38.9,37, 0 and 36.3kg .A s in former years production inherbicide-treate d plotswa s somewhat better than on plotswer e seeds inth e tree stripswer e controlled by shallow soil tillage. Mulching on the tree strip again,wa s only slightly better than leaving the grass on thealleys .

Influenceo fnitroge no nyiel dan dqualit yo ffrui t crops

InWilhelminadorp , the experiment on the nitrogen requirement of Schone van Boskoop apples inrelatio n to plant density was continued (Table 22).Th e con­ siderable drop inproductio n of trees inunfertilize d plots in 1977,a s a con­ sequence of severe drought in 1976 (Table 16,pag e 36 in theAnnua l Report for 1977),wa s again followed by a recovery-effect in 1978.Consequentl y treatments with aver y lowyiel d in0 N-plots in 1977,apparentl y showed no response to fertilization (70, 140, 210 or 280k g N perha ) in 1978 (Table23) .

39 Table 23.Averag e response of Schone van Boskoop apples in 1978 to nitrogen dressings,a s related toplan t density andwidt h of the herbicide strip.

Plant distance Herbicide Yield (kg per tree) Fruit weight (g) (cm) strips 0 N 70-280 N 0 N 70-280 N bed 13.8 12.9 180 171 300 x 102 wide 14.8 15.2 168 172 355 x 136 wide 17.1 19.0 181 187 395 x 205 wide 20.4 24.3 197 194 300 x 102 narrow 13.9 13.8 188 196 355 x 136 narrow 17.3 17.5 194 199 395 x 205 narrow 20.5 20.5 201 209

There was only a slight positive effect of nitrogen on fruit size.Th e yield data for trees inwid e herbicide strips suggest an increasing favourable effect of fertilization thewide r the trees are planted.Measurement s of stem girth in the spring of 1978 showed an increasing stem growth in the 395 x 205 cm plant systemwit h increasing nitrogen dressings.O n the contrary fertilization in the beds resulted inrestricte d stem growth. As in 1977,yiel d data of Golden Delicious and Cox's Orange Pippin apples were collected in the large field experiment on groundwater-tables, taken over from the Research Section of the IJsselmeerpolders Development Authority at Lelystad. Since 1964,th eexperimen t comprises dressings of 0-75 or 150k g N perh a on each plot inwhic h combinations of the following water-tables in winter (5months ) and in summer (7months )wer e applied: 40- 70- 110 and 130 cmbelo w surface.Th e summer level is never higher than thewinte r one.Th e experiment is situated onnewl y reclaimed lakebotto m soil in the polder Eastern Flevoland,wher e the growth of fruit trees isusuall y veryvigorous . Forbot h varieties productions in 1978 showed an interaction between response to fertilizationan d the groundwater level.I nplot swit h awater-tabl e constantly kept at 40 cmbelo w surface (winter - summer), the field on subplots dressed with 150k g N perh a increased by 150%fo r Golden Delicious and by 49% for Cox's Orange Pippin compared with unfertilized plots.O nwell-draine d plots with a constantwater-leve l kept at 130c m and consequently afa rbette r deve­ loped root system, the same amount of nitrogenbrough t about a too vigorous growth,resultin g in only a 3%highe r yield for Golden Delicious and a 14% decrease for Cox's Orange Pippin. A country-wide surveywa s started in collaborationwit h the Extension Service for Horticultural Soils, to investigate the feasibility of determining soluble nitrogen in the rooted soil profile inherbicid e strips as abasi s for fertilizer recommendations. Soil sampleswer e collected in some 40 Golden Delicious orchards,i nFebruary ,Ma y and October,an d to adept h of 100-120 cm. InFebruar y samples, amounts of nitrogen from nitrate plus ammonium ranged be­ tween 10an d 50k g N perh a inplanting s where fertilizationwa s omitted in two to four previous years:30-6 0 kg Nwa s found inorchard s annually dressed with 50-100 kg Npe r ha.A considerable increase in soluble Nwa s observed in samples collected inMay .

40 Relationship between potassium contents in apple leaves and soil

Because potassiumha sa nunfavourabl e effect onbitte r pitan drelate d disorders,ver y littleha sbee n applied inman y Netherlands orchards forsevera l years.Averag e annual dressings areestimate d at5 0k gK 20pe rha .I nsom e orchards neglected fertilizationan dimpoverishmen t ofth eK-statu s ofth esoi l have ledt osligh t initial symptoms ofdeficienc y already.Ai mo fthi s project is toanalys e soil andweathe r factors that influence potassium nutritionan d tose tu pstandard s foradequat e K-status ofth ecro p invie wo f productivity aswel l asfrui t quality andkeepability . One important factor thatha sbee n distinguished, isth ewithdrawa lo f potassiumb ya gras s vegetationwhe nmulchin g ofth emow n grass onth eherbicid e strips isapplied . Ina youn g apple orchard, replanted after apea r orchardwa s grubbed, thiswithdrawa lha sle dt over y lowpotassiu m contents inleave so f trees planted inspot swher e theforme r grass stripswer e situated. Another factor isdrought :Afte r adr yspell ,particularl y ondr ysoils ,leaf- K contents may drop considerably.O nsoil s lowi npotassium , fertilizationha sa fa rmor e favourable effect uponyiel d (fruit size) indr yyear s thani nnorma lo rwe t years. In leaves ofBeaut y ofBoskoo p apples inth eexperimen t onplan t densities atWilhelminador p contents between0.6 0an d 1.15%K wer e found. Parto fth e variations couldb eattribute d todifference s ingroundwater-leve l inth e spring. Inth eexperimen t ontrickl e irrigation,K content s inCox' s Orange Pippin leaveswer e increasingly affectedb yannua l dressings of30 0k gK2 Ope rha .I n 1976, 1977an d 1978fertilizatio n resulted in0.08% ,0.16 %an d0.30 %highe rK contents, respectively. Trickle irrigation between 1Ma yan d 15Jun e (4.61 pe r daype rtre e inaverage ) increased theK contentb y0.16% . Differences were also related tomod e ofwee d control (byherbicide s orrotar y tillage)an d mowing method (grassmulche d ontre e strips oro ngras s strips).Fo rtreatment s CC,CM ,M Can dM M(fo ra nexplanatio n seeSoi l management experiments) average contents were 1.60%, 1.44%, 1.42%an d 1.48%K ,respectively . These data suggest an interaction ofth eeffec t ofK originatin g frommulch ,wit h soil tillage: when tree strips aretreate dwit h herbicides,i.e .ar enon-tille d (CC,CM )th e uptakeb yth etree ,o fK release d fromth emow n grass isbes t when this grass isplace d onth etre e strips (CC).Howeve rwhe n thetre e strips arekep t free fromweed sb yshallo w tillage (MC,MM) ,uptak e ofthi sK i sbes t when this grass islef t inth ealle y(MM) . The positive effecto nK uptak e ofth etre eo fnon-tillag e ontre e strips whenweed s arechemicall y controlled comparedwit h tillage,wa sconfirme di n the soil management experiment atOosthuizen .Marking s forver y slight symptoms ofK deficienc y inCox' s Orange Pippin inthi s experiment averaged 0.16, 0.17, 0.47 and0.3 7fo rth etreatment s CC,CM ,M Can dMM ,respectively . Non-tillage in this experiment (CC,CM )appeare d more effective insuppressin g deficiency symptoms thandi dfou r years ofannua l fertilizationwit h 0,150 ,30 0o r45 0 kg K20pe rh a (deficiency markings 0.41,0.21 ,0.3 3an d0.2 1 respectively).

Bitter pit in apple

Present-day knowledge about bitter piti napple swa sreviewe d inth ecommu ­ nication series ofth eExperimen t Station: 'Mededeling'no .17 .Th epublicatio n comprises physiological backgrounds;a discussio n oforchard , growing, storage,

41 soil andweathe r factors;contro l and prediction ofbitte r pit. An investigationwa s started to analyse factors that influence fruit growth. Main objective is toevaluat e the influence ofweathe r conditions on fruit growth.Motiv e for this approach is the finding that years when fruits grow relatively big (bearing allowed for), usually are alsobitte r pit years.I n seven Cox's Orange Pippin orchards, two inWilhelminadorp , five elsewhere, fruit diameters were periodically measured and thedat awer e converted into daily increments in fruit volume.Th e measurements were started early inJun e taken at5-1 4 days intervals,an d terminated by the end of September. The daily increase in apparent fruit volume ranged between 0.8 and 3.4 cm .Apar t from low initial values in June and again laterwhe n ripening approached, thedail y increase showed relationships with number of fruits per tree, leaf condition, average daily maximum temperature, and drought.Belo w 17°C fruit growth rapidly decreased, especially indul l rainy periods. Cox's Orange Pippin fruits from the 1977 and 1978 crop in the experiment on trickle irrigationwer e stored and examined forbitte r pit.I n the 1977fruits , bitter pit averaged 21.8%, 13.9%, 18.3%an d 10.4%fo r the treatments CC,CM ,M C and MM, respectively. Less pitwa s found in fruits picked in 1978:3.2% , 2.3%, 0.9% and 2.1%fo r the same treatments.Th e data confirm former findings that fruits fromherbicide-treate d plots are relatively susceptible tobitte r pit, inparticula rwhe n mulching on tree strips is applied. In the same experiment a slight increase inbitte r pitwa s brought about by potassium fertilization. Trickle irrigationha d an indistinct effect. In the experiment inOosthuizen , stored Cox's Orange Pippin fruits showed 39%, 38%,32 %an d 34%bitte r pit and breakdown, as an average for the treatments CC, CM,M C and MM. The reduction inbitte r pitbrough t about by tillage on the tree strips (MC and MM), however, involved a 7%dro p in production compared with non-tillage onherbicide-treate d plots. Combinations of the factors 'pruning', 'shade in three different periods'an d 'moisture supply on ahig h level starting inApri l or shortly before, or after, termination of shoot growth'wer e applied in a pot trialwit h Karmijn de Sonna- ville apples.Th e experimentwa s started in 1977.Shad ewa s provided by plastic nets. In the small 1978 crop of fruits destined for analysis some internal pit was observed, in particular in apples from pruned treeswher ewate r supply was ample throughout the growing season and shadewa s applied between 3Ma y and 20 June. Furthermore, cracking of fruits appearing in the course of the summer was worst in unpruned treeswithou t shade,wher e after aperio d of relative drought, water supplywa s restored on 28 July. Cracked fruits had ahighe r sugar content in the juice than sound ones. Two spraying experiments on the control ofbitte r pitwer e carried outwit h Cox's Orange Pippin guard trees in two field experiments. In the first,earl y and late sprayingswit h Wuchsal Suspension 2,calciu m nitrate (flakes and prills) and calcium chloride indifferen t concentrations were compared. Slight leaf scorching was observed only in trees thatha d been sprayed twelve times with calcium chloride inconcentration s increasing from 0.26% to0.57% . The fruits are stored andwil l be analysed. Objective of the second trialwa s to assess the tolerance of leaves tohig h concentrations of calcium chloride and calcium nitrate.Bot h compounds were mist-blown indifferen t concentrations, calcium chloridewa s also sprayed. On thebasi so fequall yhig h calcium concentrations,mist-blow n chloride resulted in more leaf scorching than the nitrate.Frequen t mist-blown applications of calcium chloride in gradually increasing concentrations of 1.6t o 4.5% and 3.2 to8.1% ,b y the end of the season, gave rise to slight and severe scorching, respectively. Very light scorching was observed when calcium chloride was sprayed in increasing concentrations of 0.7% to 1.05%.

42 Trickle irrigation

In the experiment on trickle irrigation 4.6, 3.8 and 4.6 liter per tree per daywa s given on average,fo r the three trickling periods I (1Ma y - 15 June), II (15 June - 1August ) and III (1Augus t - 15 September), respectively. Consi­ dering the rather dry season of 1978,thes e quantitieswer e rather small. Tensiometer readings for instance, indicated two periods of drought (at 25 cm depth),viz .durin g 20day s between end ofMa y and 20 June and, again, from end of July till October.Howeve r the 1978 seasonwa s rather cool and dull and the quantities ofwate rwer e determined by calculation of evaporation inexces s of precipitation andb y using a reduction factor to allow for the size of the trees and leaf development.Fo r this purpose an evaporimeter was installed in the orchard at aheigh t of 1.80m , roughly flushwit h the tops of the still young trees. Comparisonwit h other data showed one third higher readings from evapori- meters in the open field compared with our own readings.Also , later in the season a comparisonwa s madewit h asecon d evaporimeter installed at 2.80 m above the ground in the orchard. These readings too, suggested a considerably evaporation at someheigh t above the crop compared with readings at 1.80m . Another reason for the possibly too low quantities ofwate r applied in this experiment,ma y be an underestimation of interception of summer rainb y tree crowns and inparticula r by grass strips. In some plots of this experiment half of the treeswer e temporarily discon­ nected from the trickle system. Here, tensiometers were installed by digging in porous pots at adept h of 25 cman d at 25 cm from the dripper. Every time when themercur y exceeded 10o r 20 cm 30 liter ofwate r was administered by trickling, in awa y comparable with trickling elsewhere in the experiment. By comparison of this 'evaporimeter-controlled' and 'tensiometer-controlled'watering , itwa s calculated that average daily quantities ofwate r were roughly twice ashig h in the second case as in the first case.Thi s result supports the impression that in the evaporimeter-controlled trickle experiment too little waterwa s given. In this experiment crop response towaterin g was very weak in 1978.A slight improvement of fruitweigh t was observed for Cox's Orange Pippin apples only. Invariou s other experiments with apple trees and small fruit,man y tensio­ meters (some 200)wer e installed at a depth of 25 cm, to investigate the in­ fluence of plant density, rain fall and interception of rain, andwatering . In dense plantings such as thebe d system and single-rows at distances of 300 x 102 cm, after awe t period the soil dries outmor e rapidly than inwide r plantings.Anothe r observationwa s that at some distance east of the stem the soil is systematically drier thanwes t of the stem.Thi s phenomenon isbrough t about by interception of rain.

Chemical weed control

P.J. Bolding

The trialwit h light vegetations under young Golden Delicious onM. 9 trees, started in 1975 in the experiment garden at Numansdorp,wa s terminated in 1978. The aimwa s to examine theeffec t of slight competition inrelatio n to alter­ natives for chemicalwee d control.Th e soil is an excellent deep-rooted marine claywit h ample moisture supply. An impression of the vegetations and their treatment is given in theAnnua l Report for 1976,p . 39.Sinc e 1976 some alterations have takenplace .Fo r instance mouse-ear (Cerastium (Dill.)L. ) and

43 stonecrop (Sedum aare L.)wer e almost entirely ousted by other weeds.Althoug h the soil moisture conditions were good,yiel d responses have been strongly in­ fluenced by a rainfall deficit inmos t of theexperimenta l years,particularl y in 1976.Mos t of the treatments showed yield depressions,u p to30% ,compare d with clean-weeding in theherbicide-treate d control plots.I n general therewa s a good relationship between yield reduction and the density of the vegetation under the trees,usually , removal of a toovigorou s growing vegetation (such as red fescue (Festuca Tubva L.) and annual meadow grass (Poa annua L.)) resulted ina strong recovery effect. It is concluded that even under good soil conditions lightweed s or sownmonoculture s of slightly competitive plants may result in too strong yield reductions. Since 1976 attentionha s been paid towil d rootstock shoot control in an apple plantation ofMelros e onM.9 .O f three herbicides tested, Dicamix-F (6 liter per ha), Tipoff (81/ha )an d Roundup (6 1/ha), the last gave thebes t results. Dicamix-F alsowa s effective. The emergence of suckerswa s distinctly suppressed after two years application of Roundup,bu t them cutting offwit h a hoe resulted in doubling the number of new suckers.A good controlwa s also obtained by application of Tipoff,bu t after two growing seasons a slight increase of newly formed shootswa s observed. The treatments were carried out between 15Jun e and early inJul y and caused no adverse effects upon thetrees .

44 PHYSIOLOGY SECTION

J.Trom p

Investigations into factors underlyingth erelationshi p between thevegetativ e and generative developmento ffrui t trees

Growth regulators

The experimentwit h Cox's Orange Pippin, started in 1976 to study the effect of afe w combinations of SADH and Gk^+y on growth and flower-bud formation of unfertilized trees and trees given either a nitrate or an ammonium dressing, gave roughly similar results in 1976 and 1977.Bot h the dressings favoured growth aswel l as flowering especially in the second year.Th e form of the given nitrogenwa s of no importance. Irrespective of the nitrogen treatment,appli ­ cation of GA^+7whethe r combined with SADH or not reduced flower-bud formation. In 1977,a pot trialwit h one-year-old Cox's Orange Pippin treeswa s commenced toevaluat e the effect of time of nitrate dressing (four dates:5 April, 31May , 26 July and 20 September) in combinationwit h an 'early' and a 'late' GAij+7treatmen t ('early':a fe wweek s after fullbloom ; 'late': shortly after growth has ceased) on growth and flower-bud formation. Shoot growth hardly responded to thevariou s treatments.Th e same holds for flower-bud formationwit h respect to time of nitrogen dressing but GA^+7ha d a reducing effect especially when applied 'late'. In ane w pot trialwit h Cox's Orange Pippin attention again isbein g focussed on growth and flower-bud formation. In successive periods of sevenweek s groups of trees given either anitrat e or an ammonium dressingwer e maintained in the horizontal position.Apar t from a few control groups each treewa s sprayed with GA^+7 afe wweek s after fullbloom . In thiswa y the flowering level is reduced somewhat.A s a consequence apromotiv e effect of thevariou s treatments may manifest itself better.

Effect of air and root temperature and light intensity on the behaviour of budded apple rootstocks

From themiddl e ofFebruar y until the end ofApri l under controlled condi­ tions,a nexperimen twa s done to study the effect of air temperature (17°an d 24°C), root temperature (10°C and the air temperature) and light intensity (about 12,000 and 21,000 lx)o n shoot growth, leaf development, dry matter production,wate r consumption andminera l composition of rootstock M.9,M.2 6 and MM.106 budded with Cox's Orange Pippin.Buddin gwa s done inAugus t 1977.A few datawil l be given.Minera l analyses are inprogress . As expected (Annual Report 1977,p . 42),shoo t growth was not orhardl y better at thehig h than at the low light intensity. Nevertheless net dry-matter production per treewa smarkedl y higher at thehig h light level,a s shownb y much highervalue s for net drymatte r production per leaf-area unity. The low root temperature reduced shoot growth.However , it only reduced dry matter production per tree at thehig h light intensity. Growth vigour was better at

45 thehig h airtemperatur e thana tth elo won ebu tth eeffec to fai rtemperatur e ondr ymatte r productionwa srathe r variable.I ti snoteworth y thatth e influence ofai rtemperatur e ongrowt h manifested itself especially inth erat e of leafing-out.Afterward s temperature effectwa smuc h less marked. Thehig h levels ofligh t intensity,ai rtemperatur e androo t temperature enhanced transpirationpe runit y oflea f area,bu tth eeffec twa susuall y small.

Seasonal variations in the mineral composition of xylem sap of apple

Xylemsa po ffull-grow n treeswa sfrequentl y analysed forpotassium , calcium, magnesiuman dnitroge n throughout 1977i nGolde n Delicious andfro mth ebegin ­ ningo fMarc h until theen do fJul y 1978i nMelrose .I ngenera l potassiumwa s the predominant element,it sconcentratio n being twot othre e times thato f calciuman dnitrogen ;magnesiu mb yfa rwa sleas tabundant .Th econcentratio no f calcium,magnesiu m andnitroge n increased during March andApri l andshowe d peak values around theen do fApril .Fo rpotassiu m amor e gradual increase culminated ina maximu m five toseve nweek s later.Afte r agradua l declineal l elements reached aconstan t lowleve li nAugust . The datama yb eexplaine d interm s ofth erelativ e importance ofth efactor s transpiration,upwar d movementb yexchang e processes andirreversibl e binding in tissues surrounding thexyle mvessels .

Effect of a few environmental factors on flower-bud formation in apple

Inth eexperimen t carried outi n197 7o nth eeffec t offou r night-tempera­ ture treatments (A:20° C throughout;B :10° Cthroughout ;C :20° C thefirs t half ofth eexperimenta l period, thereafter 10°C,an dD :th erevers e ofC ,10°C , thereafter 20°C)o nCox' s Orange Pippin (Annual Report 1977,p .4A) , flowering datawer e collected inth esprin go f 1978.Treatmen tC reduce d flower-bud for­ mation appreciably even though therewa sn odifferenc e ingrowt h vigour between A andC .Furthermor e thedat a suggest that increasing thenigh t temperaturei n themiddl e ofth eseaso n (TreatmentD )promote d flowering slightly.I ti sre ­ markable thatTreatmen t Dals o stimulated shoot growth. In another 1977experimen t againo nCox' s Orange Pippin (Annual Report1977 , p. AA),th ecombine d effects ofligh t intensity (12,000 and21,00 0 lx)an droo t temperature (10°an d18°C )wer e studied.B yfa rth elowes t levelo fflower-bu d formationwa sfoun d atth elo wligh t intensity atth eroo t temperature of18°C . For theres t therewa shardl y anydifferenc e between treatments.A clea r rela­ tionship between shoot growthan dflowerin g could notb eshown .

Pre-harvest physiology of fruits in relation to fruit quality

Effect of relative air humidity (R.H.) on shoot and fruit growth and on the mineral composition of leaves and fruits of apple

From about full-bloom until harvest three-year-old Cox's Orange Pippin trees were exposed to four air-humidity régimes at a constant temperature: A) R.H. high (85-100%) throughout; B) R.H. low (45-55%) throughout; C) R.H. low until half-way through the experimental period, thereafter high; D) the reverse of C at first R.H. high, thereafter low. Shoot growth was reduced appreciably in Treatment B compared with that in A, but there was hardly any difference in

46 fruit growth. Increasing theR.H .half-wa y through the season (Treatment C) influenced shoot growth little but enhanced fruit growth slightly. Reversely, Treatment D reduced final fruit size somewhat;agai n shoot growth was affected only little,bu t a rather severe leaf drop occurred.Analytica l data are not availableyet .

Effect of soil moisture level on shoot and fruit growth and on the mineral com­ position of leaves and fruits of apple

The outdoor pot trial started already in 1976 to study thebehaviou r of Schoneva n Boskoop inrespons e to four moisture conditions in the soilwa s ter­ minated in the current year.Th e treatments were:A )hig h (19%leve l throughout); B)hig h level untilmid-July , low (12%) thereafter;C ) low until mid-July,hig h thereafter, and D) low throughout.Furthermore , in 1978withi n each treatment two K levels in the soilwer e realized. In addition to the normal dressing as given in the previous years,hal f of the trees received an extra potassium dressing. So far the analytical data for the leaves are available. In this third experimental year inal l cases shoot growthwa s very weak; therewer e no differences between treatments.Jus t aswa s found in the two previous years,frui t growth hardly responded to thevariou s conditions. The additional potassium dressing increased the content of potassium in the leaves considerable,bu t reduced that formagnesiu m and to a lesser degree for calcium. The effect of soilmoistur e condition on thepotassiu m and calcium level in the leaveswa s small.Whe n extra potassiumwa s given, leaf potassium inTreatment s B and Dwa s lower than that inA and C, at least later in the season. This resultwa s not found with the normal dressing of potassium.

47 PLANT PATHOLOGY SECTION

H.A.Th,va n der Scheer

Apple

Canker

Research on the susceptibility of Cox's Orange Pippin apple trees to spores of Nectria galligena and the effect of inoculum dosewa s continued. Main branches of the treeswer ewounde d and inoculated with a spore suspension in November and December 1977 and inJanuar y 1978.Th e number of spores ranged from fivehundre d to fifty thousand permillilitre .Mos t of thewound s cankered after inoculation inDecember , indicating themos t susceptible time for the trees. In the spring of 1978 cankering first became visible around wounds made and inoculated inNovembe r 1977.Th e average time lapsebetwee n inoculation and visible cankering of thewound s was shorter, the laterwoundin g and inoculation was carried out in the period concerned. As in 1976/77 conidiawer e more virulent than ascospores and morewound s cankered after inoculationwit h a higher spore density. In the spring of 1976 apple canker seriously occurred on one of the trial fields of the soil fertility section.Winsto n apple trees receiving annually 250k g N/ha,wer e distinctly more attacked thanWinsto n apple trees,receivin g annually 100k g N/ha (resp. 1.4 and 0.8 cankers per tree).Mos t of the cankered patcheswer e situated around cracks in the axils of thebranche s with the stem. The results of a subsequent trial showed thatmor e artificial wounds in the mainbranche swer e cankered in trees receiving 250k g N/ha annually than in trees receiving 100k g N/ha annually.However , the difference in the number of cankered wounds between trees ofbot h groupswa s much less in 1978 than the difference in the number of cankered patches in 1976.Presumabl y inWinsto n apple trees receiving 250k g N/ha annually, cracks in the axils can occur more easily duringwinte r than inWinsto n apple trees receiving 100k g N/ha annually. These cracks are ideal entrances for the fungus.Th ehighe r incidence of apple canker in theWinsto n apple trees receiving 250k g N/ha annually compared with theWinsto n apple trees receiving annually 100k g N/ha,wa s determined more by the number of cracks in the axils thanb y increased susceptibility of the trees. In a field trial on Cox's Orange Pippin, three doses of Luxan Captan83 % spp.wer e tested for control of N. galligena. The sprayswer e applied on 28 November 1977.Befor e and after that date, the mainbranche s of the trees were wounded and inoculated with amixe d solution of ascospores and conidia.N o significant differences inth enumbe r of cankeredwound swer e observed after spraying with 0.15%, 0.25% and 0.5% Luxan Captan 83%spp. .Th e results were similar to those of sprayingwit h 0.2% and 0.5% 0rtho-Difolatan-80 and 0.5% Bayer copperoxychloride and not as good as the results of sprayingwit h 0.2% Topsin M.Al l fungicides actedbette r ina preventiv ewa y than in a curative one.Wound s thatwer e made after spraying and thatwer e inoculated after three days, remained only free from cankering if the treeswer e sprayed with 0.2% Topsin M. Once in eachmont h from September 1977 toMarc h 1978,artificia l wounds were

48 made in the mainbranche s of Cox's Orange Pippin apple trees. Sporulating pieces of cankered primings hanging in the top of the trees,serve d as inoculum sources. Manywound s cankered if theywer e made in September,Novembe r and December 1977 and January 1978.Cankerin gwa s prevented toa great extent if the trees were sprayed with 0.15% Luxan Captan 83% Spp.on ewee k after each series ofwound s wasmade ,excep t for the first series ofwound s made in September 1977.

Fruit rot, storage diseases

The effect of 0.35% Stop Scald and 0.5% BHT on scald of Melrosean d Schoneva n Boskoop appleswa s tested. The fruitswer e dipped after picking ina solution towhic h sometimes 0.1% TopsinM or 0.35% Lirotect-45Fwa s added for control of fruit rot.Thi s method of fruit rot controlwa s compared with spraying twice before picking with 0.1% Topsin M. Excellent control of scald onMelros ewa s obtained by dipping the fruits in Stop Scald solution. BHT dissolved insuffi­ ciently in thewate r and this presumably contributes to the poor control of scald by this material.Al l methods were equally poor in controlling fruit rot.

Phototoxicity

The action on scab and powdery mildew and the phytotoxic effects of some fungicides and fungicide mixtureswa s tested on Golden Delicious apple trees. All fungicide sprays gave an adequate control of the disease(s) forwhic h they were designed, 0.15% Bayleton EMbein g thebes t for control of scab and powdery mildew.Al l the fungicide sprays caused somebrow n discolouration of thepetals . Trees sprayed with 0.15% Bayleton EM showed themos t discoloured petals and gave the lowest yield.O n the average fruits from trees sprayed with 0.25% Pallinal Mwer e heaviest; those from trees sprayed with 0.2%Pallica p were more yellow than other fruits.N o significant differences in fruit russeting were observed.

Powdery mildew

Research on epidemiology of powdery mildes,cause d by Podosphaera leucotricha, inconnectio nwit h the threshold of economic injurywa s continued. In contrast to the disease progress on the trees in the isolated parcels in the previous year, the fungus had no chance to spread rapidly due to spraying eith Bayleton (inJun e replaced by Nimrod) in good time and regularly.A termination of the spraying after 22 June on parts of the parcels led to a small,bu t significant increase in the number of diseased leaves.

Scab

The epidemiology of scab,cause d by Venturia inaequalis, was also observed on the same trees in the parcels mentioned above.A s inpreviou s years,mor e scab occurred on Golden Delicious and James Grieve than on Cox's Orange Pippin and Jonathan. The termination of the sprayswit h captan after 7Jun e did not result in a significant increase in leaf and fruit attack on Cox's Orange Pippin.O n the contrary a sharp increase in leaf attack occurred after 7 June on trees of the other cultivars when the sprayingwa s terminated. In that case nomor e than 1%o f theJonatha n fruitswer e scabbed,bu t on Golden Delicious and James Grieve always more than 1%o f the fruitswer e scabbed. On one plot of Golden Delicious

49 and two plots of James Grieve all shoots had scabbed leaves at the end of the summer of 1977.Despit e sprayingwit h captan in J978, scab was present on5-8 % of the leaf rosettes originating from theblosso m buds. By a coïncidence, the spraying on these three plotswa s not terminated on 7 June;nevertheles s scab was present onmor e than 1%o f the fruits at picking.

Two new fungicides were tested for curative control of V. inaequalis on shoots of a stoolbed of apple rootstock M.2.Both ,0.1 % BTS 40542 and 0.065% Rubigan controlled the fungus equally well as the standards (0.1%Topsi n M and 0.09% Melprex), if applied 72hour s after inoculation of the shootswit h a spore suspension.

Applean dpea r

Crown gall

Inpo t trialswit h seedlingso fappl e andpea ran dwit h asexually multiplicated apple rootstocks, the effect of several parameterswa s tested on the incidence of crown gall, caused by thebacteriu m Agrobaaterium tumefaaiens. At ahighe r soil temperature (between 10an d 20°C) aswel l as at ahighe r pH-Kcl (between 5.8 and 7.6) of the infested soil more galls on the roots occurred. Heavy pruning of the roots of apple rootstock M.9 led tomor e galling along the stems after growing of the rootstocks in infested potting compost.Th e pruning wounds undoubtedly acted as appropriate entrances for the pathogen.However , if the rootstocks were planted innot-infeste d potting soil after pruning of theroots , less gallswer e present along the stems.Perhap s pruning of the roots also takes away themai n inoculum source and therefore the pruningwound s can stay free from infectionb y A. tumefaaiens. As in 1976,n o differences in susceptibility betweenvirus-fre e and virus-infected M.9 rootstocks were seen.O n the contrary the sizing of M.9 rootstocks influenced the appearance of galls:ther ewer e more on thicker rootstocks. A strong correlation existed between theweigh t of the M.9 vv apple rootstocks atplantin g time and theweigh t increase after one year growth in potting compost (r =0.99) . The correlation between theweigh t increase and the increase inste mcross-sectio nwa s stronger than thatbetwee n theweigh t increase and the total length of this year's growth (resp.:r = 0.75 and r= 0.55)* . In a field trial and in anumbe r of pot trials crown gallwa s not controlled by dipping seeds or rootstocks or drenching potted rootstocks with suspensions of the antagonistic 'strain 84'o f A. radiobaater, isolated inAustralia . On closer investigation, Drs H.J. Miller (PlantProtectio n Service, Wageningen) isolated pathogenic Agrobacteria from the developing galls,whic h belonged to thebiotyp e 1an dwer e insensitive to thebacteriocin e of 'strain 84'.Thes e pathogenic isolates were also insensitive to streptomycine.Probabl y this explains the failure of Fytostrep 60 to control the gall development in three out of four trials.Als o AAventa-46, applied as adip ,di d not control the disease. As in 1976,Fytostre p 60depresse d the growth of the apple seedlings.Thi s growth depression aswel l as that caused by regularly picking of the leaves during the growing season did not effect thenumbe r of galls per seedling.

* r= correlation coefficient.

50 Strawberry

Alternaria leaf spot

Inco-operatio nwit hth eExperimenta lGarde na tBreda ,a fiel d trialwa s carriedou tt ocontro l Alternaria alternata, causinglea fspot so nSivett a plants.Regula rsprayin gwit h0.15 %Rovra lcontrolle d thedisease ,bu tsprayin g with0.2 %Luxa nTMT D80 %Spp .gav en ocontro la tall .Applicatio no feac ho f thefungicid espray sresulte di nth eproductio no fmor erunner spe rplan ti n August 1977an da nincreas ei nyiel d in 1978i ncompariso nwit hunspraye d plants.

Red stele

Thefungu s Phytophthora fragariae, theoriginato ro fre dstele ,wa sstil l presenti nsoi lsample sfo rthirt ymonth sa t4° Ci nclose dplasti cboxe s. Inpo ttrial sth einfluenc eo fplan tspecie san dcro prelatio no nth e infestationo fsoi lb yP . fragariae wasinvestigated .Hal fo fth epot swit h soiluse di na nexperimen ti n 1976(se eAnnua lRepor tfo r 1976,p .46 )wer e subsequentlyplante du pi n 1977wit hSeng aSengan astrawberr yplant sa ssecon d crop,th eothe rpot swit hsoi lwer e leftfallow .A tth estar to f 1977P . fragariae couldn olonge rb edetecte d insoi lunde rSilet zstrawberr yplants , cornsalad ,flax ,o rperennia lry egrass .B ygrowin gth eSeng aSengan astraw ­ berryplant si n 1977,soi linfestatio nbecam edemonstrabl eagai ni nth esoi l previouslyplante dwit hcor nsala d {Valerianella loousta), flax (Linum usitatissimwn), andperennia lry egras s (Lolium pererme), butno ti nth esoi l previously plantedwit hth eSilet zstrawberr yplants .Infestatio no fth esoi l couldstil lb eshow ni n 1978unde rSeng aSengan astrawberr yplant swit hothe r precedingcrop sgrow ni ntha tsoi li n 1976.Th efungu swa sn olonge rdetectabl e insoi lkep tfallo wi n 1977.I n 1978,th esituatio ni nth epot sconcernin gth e detectable soilinfestatio nwa sno taltere db ygrowin gSeng aGigan astrawberr y plantsa sthir dcrop . Inanothe rpo ttria lth eeffec to fperennia lry egrass ,Silet zstrawberr y plantsan dSeng aSengan astrawberr yplant so nth esoi linfestatio nwa steste d again.Alread yfro mth ebeginnin gsoi linfestatio nwa sonl ydetectabl e ina smallnumbe ro fpots ,an d thisnumbe rdecline d inal lo fth etreatment sdurin g thetrial .

51 Entomology Section

D.J. de Jong

Integrated pest control in orchards

Pit fruit

Research on selective supervised (integrated) control ismodifie d into the amelioration of the actually applied supervised control.I n cooperation with extension servicesw e have developed schemes that aremor e attractive tocon ­ sumers and better for the environment. Both schemes inwhic h less poisonous pesticides (including the newer pyrethroids) are used, and 'early' programmes inwhic h theus e of pesticides is omitted after ca. 15July ,ar e applied. The catches inpheromene-trap s in June gave less reliable information on the necessity for spraying of the young larvae in June-July, than sampling of the larval population of the summer fruit tortricid Adoxophyes orana inMay . This country-wide studywa s done togetherwit h Ir S. Stamenkovic and extension services. In June the larvae of A. orana were controlled excellently by either one or two applications of the pyrethroids permethrin, decamethrin and fenvalerate gave excellent control of the larvae of A. orana inJune . The initial mortalities of young larvae of A. orana on residues ofazinphos - methyl, pyrethroids and some other insecticides,wer e disappointing incompari ­ sonwit h earlier results.Test s havebee nmade ,i n order todetermin e whether the susceptibility for insecticides has decreased. Studies are made on the influence of dense plant systems and spraying techniques ('adapted' spraying machines) on the quality of insect control.Pes t control on,fo r instance five-row-plant systems,wa s difficult or inadequate. Field trialswer e carried out to test the effect of less poisonous insecticides on the apple clearwing moth Synanthedon myopaeformis, the pear psyllid Psylla pyri and the apple leaf gallmidge Dasyneura mali. Because of a good ovicidal effectbu twithou t larvicidal action,diflubenzuro n gave a good but slow reduction of thepopulatio n of pear psyllids.Th ebette r penetrating organophosphorous compounds mevinvos and metidathion are probably more effective in reducing the larval population of Dasyneura mali in leafrolls. Control of thehibernate d larvae of Synanthedon myopaeformis seems tob e possible with Decis 0.1% and ThiodanM.O .2% .

Strawberry

The strawberry weevil Anthonomus rubi has become more abundant and for adequate control there are problems with spraying residues and beekeeping in the cultures.Preliminar y studies of thebiolog y and phenology indicate the importance of thebehaviou r of thebeetl e for control.Th e presence of the species onwil d plants, the interactionbetwee n the culture fields,an d the dispersal of thebeetles ,complicat e good and 'safe'control .A s the straw­ berries havebud s over a long period, production for five or sixmonth s in the

52 seasonhamper s adequate reduction and regulation of the population. There is only one generation and thebeetle s start egglaying after hibernating, what gives points of application for control.

53 ECONOMICS SECTION

J. Goedegebure

Production costs of fruit-tree growing on a fruit holding

Due to the increasing orchard density, the relative scarcity of fruit trees and thewea k liquidity position of fruit holdings, several fruit growers have been raising their own trees instead ofbuyin g them from specialized nurseries. In 1978 a research was carried out into the production costs and the business expenditures of fruit-tree growing on fruit holdings.Attentio nwa s also paid to other factorswhic h may nothav e any direct financial consequences. The production costs arehighl y dependent on the number of trees that at the end of the nursing process mayb e regarded as trees of sufficient quality (Class A). In Tabel 24 the results are summarized.

Table 24.Productio n costs and business expenditure per tree of fruit trees grown on a fruitholdin g at different budtake percentages.

Growing Bud- Maid =ntree s Two- year-old trees method take prod, business prod, business (%) costs expend. costs expend.

full-field 60 Dfl. 4.00 Dfl. 2.31 Dfl. 5.15 Dfl. 2.99 70 ii 3.46 ti 2.01 u 4.44 2.59 80 H 3.05 M 1.78 it 3.91 2.29 90 ti 2.74 11 1.61 ti 3.50 2.06 intercropping 60 u 3.41 11 1.94 ii 4.16 2.35 70 tt 2.95 11 1.69 u 3.59 2.04 80 it 2.61 11 1.50 it 3.17 1.81 90 u 2.34 11 1.36 u 2.84 1.63

On an average fruit growers regard abudtak e of 80%a s normal.O n thatbasi s the production costs ofmaide n trees amount toDfl .3.0 5 per tree. If the trees are grown as an intercrop between the rows of ayoun g production unit, the costs areDfl . 2.61 per tree.A t abudtak e of 80%busines s expenditure is about 58% of total production costs. Business expenditure aswel l as production costs are considerably lower than the prices of trees purchased from specialized nurseries. Apart from lower costs and expenditure the following advantages of tree growing onfrui tholding s became apparent: - Tree quality canb e influenced directly by the grower and can largely meet his own specificwishes ; - After lifting up, the trees canb e replanted within a short timewhic h en­ courages afavourabl e regrowth; - Long distance transport and boxing up are avoided which limits tree damage considerably; - Inyear s of limited supply the availability of trees in insured; - Onyoun g or partly productive holdings free capacity (labour) canb e utilized.

54 Some important disadvantages are: - In general fruit growers are inclined tous e treeswhic h do not meet quality standards so that theyoun g orchard develops more slowly and production capacity, is affected; - In some cases too little attention ispai d to the quality of the rootstocks and buds; - Insom e cases the professional skill of the fruit growers is insufficient. The possibilities to supplement this shill are often limited.

55 LIST OF CHEMICALS,mentione d in this report

Commercial product Contains:

Means for preservation

BHT 100% 2,6-ditert.butyl-4-methylfenol Stop Scald 70% ethoxyquin

Fungicidesan dBactericide s

AAcaptan M 50% captan + 15%mane b AAventa-46 5.2% organic mercury Bayer copperoxy- chloride 50% copperoxychloride Bayleton 5% triadimefon Bayleton EM 0.8% triadimefon + 50%totylfluanid e BTS 40542 25% prochloraz Fytostrep 60 4 g/1 streptomycine Lirotect-45 F 45% thiabendazole Luxan Captan83 % Wettable Powder 83% captan Luxan TMTD80 % Wettable Powder 80% thiram Melprex 65% dodine Nimrod 25% bupirimate Ortho-Difolatan-80 80% captafol Pallicap 16.7% nitrothal-diisopropyl +55.3 %capta n Pallinal M 12.5% nitrothal-diisopropyl + 60%metira m + 15%mane b Rovral 50% iprodione Rubiga n 6% fenarimol Topsin M 70% thiofanaat methyl

56 Growth regulators, chemical thinners

Amex-A 820 47.3 N-sec-butyl-4 tert-butyl-2,6-dimitroaniline Alar-85 85% N-dimethylamino succinic acid (SADH)

Berelex A3 1 tablet contains 0.9g gibberelli c acid (A3) Ethrel-A 480g ethephon/lite r FR 570/3 M&B 25,105 (active ingredientno treleased ) Harvade 50% 2,3dihydro-5,6-dimethyl-l, 4 dithiin 1,1,4,4 tetroxide WK-Surfactant 90% dodecyl ether ofpolyethylen e glycol

Herbicides

Dicamix-F 2.5% dicamba + 24.2% 2.4D + 25% MCPP Roundup 36% glyfosfaat Tipoff a-naphthaline

Insecticides

Ambush 25% permethrin Decis 2.5% decamethrin Dimilin 25% diflubenzuron Ripcord 40% Cypermethrin Sumicidin 10% fenvalerate ThiodanM.O . 4.23% endosulfan+ 63 %mineral-oi l

57 PUBLICATIONS

Bulletins andnote s

This year theseventeent h bulletin ofth eResearc h Stationwa spublishe d called 'Stip inappels ' ('Bitterpi ti napple '- Dutc hwit h anEnglis h summary) writtenb yP .Delve r andbulleti n number 190o fth eAgricultura l Economics Research Institute (LEI)i nTh eHagu e called 'Enkeleverschille n ind ebedrij fs - uitkomstenva nfruitteeltbedrijven ' ('Some causeso fdifference s inholdin g results offruitholdings '- Dutch )writte nb yJ .Goedegebure .

Other publications

Bootsma, J.H. (Openda ya tth eexperimenta l garden 'DeMeergronden ' onth e23r d ofAugus t 1978. Thesuppl y ofwater ,a centra l theme.) Deope nda go pproeftui n'D e Meergronden' op2 3augustu s 1978.D ewatervoorziening , eencentraa l thema. De Fruitteelt 68(1978)31:1039-1040. (Dutch).

Buban, T., A. Varga, J. Tromp, E. Knegt and J. Bruinsma (Effects ofammoniu m andnitrat e nutrition onth elevel so f zeatinan damin o nitrogen inxyle msa po fappl e rootstocks.) Zeitschrift fürPflantenphysiologi e 89(1978)4:289-295. (German).

Caron, J.E.A., T. Kooistra and H.A.Th, van der Scheer Trials onth ephytotoxicit y ofsom ebactericide s against fireblight . Acta Horticulturae 86(1978):87-93. (English).

Delver, P. (Causes, fight against andpredictio n ofbitte r pit.) Oorzaken,bestrijdin ge n voorspellingva nstip . DeFruitteel t 68(1978)7:212-217. (Dutch). (Changes inth efertilizatio nwit h nitrogen Ian dII. ) Verandering ind estik ­ stofbemesting Ie nII . DeFruitteel t 68(1978)9:284-287 and10:324-337 . (Dutch). (Newexperience s onorchar d nutrition.) Neue Erkenntnisse inde rObstbaum ­ düngung. ObstbauWeinba u 15(1978)1:4-7 and 19-20. (German).

Dijkstra, J. (The supply ofwate r forgrowin g small fruits.) Watergevenbi jkleinfruitge - wassen. Groenten enFrui t 34(1978)21:56-57 andD eFruitteel t 68(1978)49:1532- 1535. (Dutch).

Elema, R.K. (Strong,bu tals owea k point forth eDutc h Fruit Industry.) Sterke,maa roo k zwakke puntenvoo r deNederlands e fruitteelt. DeFruitteel t 68(1978)12:396- 399. (Dutch).

58 Elema, R.K. and H.J. Mandersloot (Integrated and supervisedcontro l ofpest s also elsewhere in Europe.) Geïnte­ greerde en geleidebestrijdin g ook elders inEuropa . DeFruitteel t 68(1978) Kerstnummenr:1508-1511. (Dutch).

Goddrie, P.D. (Again:Généra l Leclerc.) Nogmaals:Genera l Ledere. DeFruitteel t 68(1978)45: 1375. (Dutch). (New English apple varieties.) Nieuwe Engelse appelrassen. DeFruitteel t 68 (1978)46:1399. (Dutch). (Mutations inpea r varieties in thepas t and today.) Mutaties bij peren, historie enheden . DeFruitteel t 68(1978)49:1544-1547. (Dutch).

Goedegebure, J. (Some causes of differences in the financial results of fruit holdings.) Enkele oorzakenva nverschille n ind ebedrijfsuitkomste nva n fruitteeltbedrijven. De Fruitteelt 68(1978)45:1378-1381 and Bedrijfsontwikkeling9(1978)5:475-480 . (Dutch). Business economic aspects of high density plantings in theNetherlands . Acta Horticulturae 65(1978):21-29 . (English).

Jong, D.J. de and H. Beeke Effect of spring application of an insect growth regulator (IGR)o n the popula­ tiondevelopmen t of the summerfruit tortricid Adoxophyes orana (F.v.R.) in an apple orchard in the Netherlands. Mededelingen Faculteit der Landbouwweten­ schappen Rijksuniversiteit Gent 42(2):1373-1381 . (Dutch).

Lemmens, J.J. (Pruning still asks our attention.) De snoeiblijf t onze aandacht vragen. DeFruitteel t 68(1978)4:118-121. (Dutch). (Experiences with summer pruning.) Erfahrungen mit Sommerschnitt. Obstbau 3 (1978)6:172-176. (German).

Mourik, J. van, D.J. de Jong and H. Beeke (The apple leafminer.) De appelvouwmijnmot. De Fruitteelt 68(1978)9:244,245 and 248. (Dutch).

Nijsse, L. (The cultivation of strawberries under plastic tunnels.) De aardbeienteelt onder plastic tunnels. De Fruitteelt 68(1978)9:303-305. (Dutch).

Oosten, A.A. van (New varieties of currants and blackberries.) Nieuwe rassen bij bessen en bramen. De Fruitteelt 68(1978)9:290-291. (Dutch).

Oosten, H.J. van (Peardecline ,a degeneration disease of pear.) Pear decline,ee n degeneratie- ziekte van peer. De Fruitteelt 68(1978)8:249-251. (Dutch). Effect of initial tree quality onyield . Acta Horticulturae 65(1978):123-128 . (English). High working for control of vigour in apple trees. Acta Horticulturae 65(1978): 1520-1523. (English).

Oosten, H.J. van and S.J. Wertheim . (Pomological research inEngland. ) Fruitteeltkundig onderzoek in Engeland. DeFruitteel t 68(J978)Kerstnummer:1520-1523. (Dutch).

59 Scheer, H.A.Th, van der Research on supervised or integrated control of diseases in apple in the Netherlands. In:Lutt e dirigée, contre lesmaladie s cryptogamiques des arbres fruitiers 1978:95-97. Uitgave:Centr o di Studio diFitofarmacia ,Universit a degli Studi Bologna. (English). Chipping of coppings and the risk of Nectria galligena attack in apple orchards. Mededelingen Faculteit der Landbouwwetenschappen Rijksuniversiteit Gent 43(1978): 831-836. (English). Overwintering of the pathogen and rating of 'secondary mildew' in relation to susceptibility of applevarietie s to Podosphaera leucotricha. Mededelingen Faculteit der Landbouwwetenschappen Rijksuniversiteit Gent 43(1978):901—907. (English). (Research to crown gall in fruit trees.) Onderzoek naarwortelknobbe l bij vruchtbomen. Gewasbescherming 9(1978)4:97-101. (Dutch).

Scheer, H.A.Th, van der, J.P.A. van Dieren and H.J-. Wondergem (Research to crown gall onfrui ttrees ,cause d by Agrobacterium tumefaciens.) Onderzoek naarwortelknobbe l bij vruchtbomen,veroorzaak t door Agrobacterium tumefaciens. De Fruitteelt 68(1978)8:246-248. (Dutch).

Schottens, A. (Is there a future for the cultivation of sweet cherries in Holland?) Heeft de teeltva n zoete kersen nog toekomst inNederland ? De Fruitteelt 68(1978)27: 910-912. (Dutch). (Experimental garden 'Midden Nederland' at Geldermalsen.) Proeftuin 'Midden Nederland' te Geldermalsen. DeFruitteel t 68(1978)31:1026-1027 . (Dutch). (New cherries ind e Betuwe.) Nieuwekerse n ind e Betuwe. Groenten enFrui t 34(1978):61. (Dutch).

Tromp, J. (Quality of Golden Delicious.) Kwaliteit van Golden Delicious. De Fruitteelt 68(1978)7:206-210. (Dutch). (Theeffec t of root temperature on the absorption and distribution of K, Ca, andM g in three rootstock clones of apple budded with Cox's Orange Pippin.)

Uitterlinden, L. (Tree shapes and planting systems in evolution.) Boomvormen en plantsystemen in beweging. De Fruitteelt 68(1978)6 :174-179. (Dutch).

Wertheim, S.J. (Dutch experiences with the thinner Amid thin.) Nederlandse proefervaringen met het dunmiddel Amid thin. De Fruitteelt 68(1978)18:596-597. (Dutch). Pruning of slender spindle type trees. Acta Horticulturae 65(1978):173—180 . (English). Intensive apple orchards with slender spindles.Act a Horticulturae 65(1978): 209-216. (English). Manual and chemical induction of side shoots on growing apple buds in the fruit-tree nursery. ScientiaHorticultura e 9(1978)4:337-345. (English).

Wertheim, S.J. and J. Westerlaken (Planting system and fruit quality.) Plantsysteem envruchtkwaliteit . De Fruitteelt 68(1978)7:200-204. (Dutch).

60 Wertheim, S.J., A. Saholtens and J.H. Bootsma (Chemical thinning ofbiennia l cultivars.) Het chemisch dunnen van enkele beurtjaargevoelige rassen. De Fruitteelt 68(1978)17:558-559. (Dutch).

Wertheim, S.J. and B. Witteveen (Regrafting for pollination improvement,a debatable affair.) Omenten terver ­ betering van debestuiving ; een aanvechtbare zaak. De Fruitteelt 68(1978)48: 1545-1455. (Dutch).

Miscellaneous publications

(Experimentswit h virusfree trees of apple and pear.) Ervaringen met virusvrije bomenva n appel enpeer . Voorlichtingsbrief no. 7,Jul y 1978. (Dutch).

Research Station for Fruit Growing inWilhelminadorp . English 'folder'wit h information on the research inWilhelminadorp . (Dutch). Bulletinso fth eResearc h Station forFrui t Growing

11. H.A.Th, van der Scheer: Fruitro tan dfrui t skin injuries inappl e (Dutch),4 0p p April 1972 ƒ 2,50

12. S.J. Wertheim and J.J. hemmens: Planting systems forappl e andpea r (Dutchwit ha n English summary), 77p p February 1973 outo fprin t

13. M. van de Vrie: Miteso nfrui t trees (Dutch with anEnglis h summary),6 8p p December 1973 outo fprin t

14. 15thLis to fFrui t Varieties (Dutch), 136pp .. Novembe r 1974 outo fprin t

15. J. Goedegebure: Economical aspectso f intensive apple plantings (Dutchwit ha n English summary),4 5p p November 1976 f10, —

16. J. Tromp and S.J. Wertheim (Ed.):Outloo ko n fruit quality (Dutch),20 2p p August 1977 ƒ12,5 0

17.P . Delver: Bitterpi ti nappl e (Dutchwit h anEnglis h summary), 128p p December 1978 ƒ15, —

Publicationso fth eNationa l Fruit Advisory Servicean dth eResearc h Stationfo r Fruit Growing

1. Strawberries inth eope n (Dutch),6 4pp . (2nded .revision ) October 1977 ƒ 7,50

2. Glasshouse strawberries (Dutch),6 4p p March 1974 inreprin t

3. Bushan dCan e fruits (Dutch),7 2p p February 1976 ƒ 7,50

4. Blueberry growing (Dutch),3 2p p June 1979 f 5,00

The Bulletins andPublication s listed onthi s pagewil lb esen tpostpai d upon receipto fi ninternationa l postalmone y order forth eappropriat e amount. Please indicate your order clearly.

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