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 members will 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. Some results are mentioned here forDiscover y and Cox's Orange Pippin. The trial onDiscover y was 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 colour was detrimentally affected (from4 2 to 28%k gwit h well-coloured fruits).