Management of High Density Pear Orchards - Virtual Orchard

Management of HighDensity Pear OrchardsT. Deckers and H. SchoofsRSF - Royal Research Station of Gorsem*, Sint Truiden, BelgiumPresented at the 44th Annual IDFTA Conference, February 17-21, 2001, Grand Rapids, Michigan.The longevity of a pear orchard incomparison with an apple orchard ismuch longer. A 10-year-old apple orchardis considered an old orchard with problemsof insufficient fruit quality (fruit sizeand/or fruit color) and should bereplaced. A high density pear orchard atthe age of 10 years is still a young orchardthat comes into optimal productivity for aperiod of at least 20 years. The higher theplant density, the more difficult it will beto keep the orchard in the productivephase. In this paper we discuss differentplanting systems for high density pearorchards and the problems of excessivevegetative shoot growth that often occurduring an “off” year after frost damage.Crucial in the management of high densitypear plantings is the definition of goodflower bud quality with a high potentialfor fruit set.PLANT MATERIALFor pear trees planted in high densityplanting systems the quality of the plantingmaterial should be high. It should be a 2-year-old tree with six to eight laterals obtainedby pruning back the 1-year-old treesin the fruit tree nursery. There is an importantdifference in productivity between a 1-year-old feathered tree and a 2-year-oldfeathered tree during the first year afterplanting. When a 1-year-old whip is planted,the productivity will be delayed by a periodof 2 years during which the frame ofthe tree has to be developed. For intensivehigh density pear plantings only 2-year-oldtrees are recommended. All the lateralsshould not be kept at the start but should bereduced to the final number wanted in theplanting system, e.g., two in the free spindleor four in the V-hedge system. Delayingthis reduction in number of laterals to alater date, when the trees are 4 to 5 yearsold, is risky and can cause a problem of asilver leaf attack. Many times this silver leafattack is a reaction to a physiological stresssituation (heavy pruning cuts) and cannotbe related to the fungal attack of Stereumpurpureum.HIGH DENSITY PLANTINGSYSTEMS FOR PEARThere are tree planting systems that arevery well adapted for high density pear orchards:the V-hedge system, the Tiensehedge system and the free spindle system. Ashort description of each of these systems isgiven.V-Hedge SystemIn this system we start with 2-year-oldpear trees on Quince C rootstock. Fourequally developed feathers are chosen andkept as fruiting branches. These branchescan be considered as four central leaders onone stem starting at approximately 60 cm(24 inches) above the bud union. The fourfruiting branches are not pruned back atplanting and are bound on a bamboo stick.At the top of each fruiting branch, the narrowangled shoots are removed in a veryearly green pinching. In the first year afterplanting these four central axes are coveredwith flower buds. Each flower bud can beconsidered a mixed structure containing theflower bud structure with one or two vegetativebuds at the base of the flower budfrom where the shoots will start during thesecond growing season. All the long andstrong 1-year-old shoots should be removedat any time. It is clear that the classical flowerbud formation on the 2-year-old wood isnot important in this pruning system. AfterA high density pearorchard at the age of10 years is still ayoung orchard thatcomes into optimalproductivity for a periodof at least 20 years.4 years the final height of the trees of about2.2 m (7.2 ft) is reached and then the prolongationshoot is pruned back into the dormantbuds at the base of the shoot. Thispruning results in a limited growth reactionof two to three shoots starting from the dormantbuds. During the next winter, thispruning can be repeated by pruning back onthe lowest growth reaction and by pruningagain into the dormant buds. The conceptis to keep the vegetative growth on this placeTHE COMPACT FRUIT TREE, VOLUME 34, NUMBER 4, 2001 117

in the tree and that the apical dominancefrom these terminal shoots controls theother growth reactions on the same branch.The productivity in this V-hedge system isbased on flower buds on short spurs and onbourse shoots on the four central leaders.The planting distance in the V-hedgesystem is 3.5 x 1.25 m (11.5 x 4.1 ft) whichmeans 2057 trees/ha (833 trees/acre). Theopening of the V is 1.4 m (4.59 ft) at 2 m(6.56 ft) height. There are more intensiveV-planting systems with 3.2 x 0.8 m (10.5 x2.62 ft) planting distance with 3516 trees/ha(1423 trees/acre) and with a more narrowopening of 1.2 m (3.94 ft). Under our climatologicalcircumstances it is difficult toallow sufficient light penetration in thesemore intensive V-hedges so flower bud formationis more variable in the intensive V-hedge systems. A disadvantage of this V-hedge system is the high amount of laborwhich is necessary.Tiense Hedge SystemIn this system we start with 2-year-oldtrees on Quince Adams rootstock also withat least four equally developed feathers onone stem. Two feathers are placed at plantingin the row direction and attached on awire. The two other feathers are placedperpendicular to the row direction andshould help to bring the trees into earlyfertility. The central leader is pruned backto about 70 cm (27 inches) above the lowestscaffold branches and the narrow angledgrowth reactions to that pruning cutare used to form the second level of scaffoldbranches. This operation is repeatedfor level three and four of the scaffoldbranches. Only two scaffold branches arekept on each level and they are bound ontothe wire structure. The fruit is hangingpredominantly on the short fruiting spurson these limbs and these structures are renewedby pruning them once they getolder. The top of the tree is composed ofthe last two scaffold branches. The plantingdistance in this hedge system is 3.5 x 1.75 m(11.5 x 5.7 ft) which means 1632 trees/ha(661 trees/acre).TABLE 1Flower bud quality on young Conference pear trees.Free Spindle SystemIn this system we also start with 2-yearoldtrees on Quince Adams rootstock withmany well-developed feathers. At plantingthe number of laterals is limited to twofeathers in the direction of the row whichare chosen with a distance of about 15 cm(5.91 inches) on the central leader. Thesetwo laterals are tied to an angle of about45˚. The central leader as well as the twolaterals is left unpruned. At the end of theunpruned central leader, competing lateralswill develop and they have to be removedin a very early stage at a length of about10 cm (4 inches).The many flower buds on the centralleader and on the laterals result in earlyproductivity and also in a good start forhorizontal branches starting from thebourse shoot. The first growth reaction onthese flower buds will be a short bourseshoot of 10 to 15 cm (4-6 inches) endingon a flower bud. The next year this shortbrindle shoot will develop to a long shootof more than 50 cm (19.7 inches). And inthe third year this long shoot will be coveredagain with short brindle shoots.This sequence of short–long–shortshoots on the central leader is very importantfor the free spindle training system.The fruit bearing wood is systematically renewedas much as possible by keepingstrong 1-year-old shoots that are coveredwith flower buds in the second year andwill bear fruit during the third year.When the trees are in a good balancebetween vegetative and generative growththere will be part of the flower buds on the2-year-old wood in lateral position. Theseflower buds are later in phenological developmentwhich is an important factorwhen frost damage occurs. The productivityof the trees in the free spindle system ismainly on the short brindle shoots on the2-year-old wood and on spurs on thebourse structures. In this training systemthe fertility of the flower buds on the 2-year-old wood is important. Conservationof some upgrowing new growing shootsleads to differences in branch diameter andindicates the way of natural growth of the# flower clusters/fruiting branch # flowers/cluster1998 1999 2000 1998 1999 2000on 2-year-old wood 8.10 4.15 9.63 6.29 4.91 6.05on 1-year-old woodin lateral position 7.05 1.85 1.12 7.25 6.68 3.23in terminal position 0.95 0.85 0.19 11.99 9.75 5.13fruit tree. These differences in twig diameterare more accentuated during the seasonby the natural bending tendency of thetwigs under the weight of the leaves on the1-year-old shoots and under the weight ofthe fruits in terminal position on the fruitbearing twigs.The planting distance in this system is3.75 x 1.5 m (12.3 x 4.9 ft) which means1777 trees/ha (719 trees/acre). An advantageof this system is the relatively lowamount of labor needed for training andpruning.FLOWER BUD QUALITYThere are important differences inflower bud quality on pear trees. The bestflower bud quality on pear trees can befound on the terminal flower buds on theshort brindle shoots (Table 1).The highest number of flowers percluster was found on the flower clusters interminal position on the 1-year-old woodwith more than 10 flowers per cluster. Thenumber of flowers per branch can varyconsiderably between years when countedon comparable places in the tree. Sometimesthe crop load can explain these differencesbut sometimes there are other determiningfactors such as climatologicalfactors. For the flower buds on the 1-yearoldwood the growth situation on theshoots has an important influence: late regrowthreactions during season can bevery negative for flower bud formation onthe 1-year-old wood.The number of flowers per cluster is animportant parameter of flower bud quality.The highest number of flowers per clustercan be found on the terminal buds ofthe short brindle shoots. In some years thenumber of flowers on this place varies between10 and 15 flowers per cluster whilethe flower buds on the 2-year-old woodhave only 5 to 7 flowers per bud.The number of leaves is also an importantflower bud quality criterion. Flowerbuds without leaves have a very low fruitset capacity; they occur on the 1-year-oldshoots with late regrowth reactions; thereis apparently a competition between thisregrowth and the flower bud formation.The presence of a bourse shoot at the baseof a flower cluster significantly increasesthe leaf area of a flower cluster. Theseleaves around the flowers increase the fruitset capacity of the cluster.The total weight of a flower bud alsocan be a good indication for flower budquality and can be determined on differentphenological stages.Internal flower bud quality criteria alsoexist. The number of seeds per fruit is118 INTERNATIONAL DWARF FRUIT TREE ASSOCIATION

important for the normal fruit development;this number should be ten undernormal pollination conditions but is oftenmuch lower in reality. For pear cultivarssuch as Conference a total parthenocarpicfruit set is possible when the seeds are destroyedin an early stage during night frost.Parthenocarpic fruits of Conference are 5to 10 mm (0.2 to 0.4 inches) smaller infruit size than standard fruits with seedsof the same pear cultivar. The number andthe dimensions of the styles and the anthersare good indications of flower budquality on pear trees. The number of stylesis normally 5 and the number of anthersis normally 20. Flowers with weaker flowerbud quality often show a reduced shape ofstyles and/or anthers. Also the length ofthe flower stalk is a quality criterion. Flowerswith a short stalk have a very low fruitset capacity. Some flower bud quality parametersare not visible such as thelongevity of the nucellus. For the pear cultivarDoyenné du Comice this longevity ofthe nucellus is limited in time and is one ofthe reasons for the difficult fruit setting ofthis cultivar (Demayer and Deckers, 1984).Nitrogen can have a positive influence onthe longevity of the ovule and can increasethe effective pollination period (EPP).FLOWER BUD POSITIONNot only the internal structure of aflower bud is important but also the positionof the flower bud on a fruiting branch.In our fruit set trials high fruit set percentagesare often found for the flower buds interminal position (Table 2). This is knownvery well by the pear growers and thereforeeach fruiting branch is pruned back ontoa flower bud on the 2-year-old wood or ona brindle with a terminal flower bud.There are also important differences infruit set percentages between years on thesame phenological stage. For young peartrees the fruit set percentages of the flowerson the 1-year-old wood in lateral positionare also good and the fruit quality of thesefruits at harvest is sufficient. For older peartrees there is often a risk for insufficientfruit quality of these fruits with a reducedfruit size. The flower buds on the 1-yearoldwood in lateral position can be considereda reserve of flower buds with adelay in phenological evolution of about2 weeks that can be very useful in yearswith frost problems during bloom.branch in comparison with the flowerbuds on the underside of the same branch.This preferential development of structureson the upper side by pear trees is notonly true for flower buds but is also presentfor the development of shoots andbourse structures. In this regard it is importantto realize that orientation canchange during the vegetation periodthrough the weight of the leaves and/or thefruits. With this process of natural bending,there is often an induction of a growthreaction just before the arc on the fruitingbranch. This growth reaction can be consideredthe future fruiting branch but isalso an important factor for vegetativegrowth control on the whole branch. Romand Barritt (1990) found on apple treesthat there was a better fruit quality (fruitweight) for the fruits produced on buds inthe upright position. Volz et al. (1992) confirmedthat for Granny Smith there is alsoa difference in fruit quality between fruitsin different positions: the fruits on the 2-year-old wood and on the 1-year-old woodin terminal position are comparable inTABLE 2fruit weight while the fruits on the 1-yearoldwood in lateral position were significantlylower. They found also differencesin mineral composition of the fruits withthe best Ca content for the fruits on the 1-year-old wood in terminal position. Thiscould be linked with a significantly higherleaf area per bloom cluster.For Conference pear trees, the situationis similar with very good fruit size for thefruits on the short brindle shoots in terminalposition and for the fruits producedon well-developed 2-year-old branchespruned back into the flower buds.The differences in development for differentorientations are not only present forthe flower clusters but also for the shootdevelopment on a fruiting branch. Brunnerand Kecskes (1990) described thebranching pattern of apple and pear cultivarsas epitonic, while the development ofthe branches above the horizontal isstronger than under the horizontal. Thesedifferences in development of the branchesare also reflected in differences inbranch diameter and indicate the naturalFruit set % on young Conference pear trees for flower buds in different positions.% fruit set in 1998 after % fruit set in 1999 afterflower drop June drop flower drop June dropon 2-year-old wood 3.34 0.13 21.51 9.00on 1-year-old woodin lateral position 8.95 2.16 39.70 13.47in terminal position 11.94 2.24 34.23 11.91FIGURE 1Dominant (Twig A) and dominated (Twig B) branches on a fruiting scaffold limb of pear. Twigs Aand B are both 2-year-old twigs on an older fruiting limb. On the places (1) and (2) we can see areduction in branch diameter caused by the presence of Twigs A and B. This reduction in diameterindicates the natural tendency of the branch to grow to Twig A. We consider Twig A the dominanttwig. Twig B and all structures farther away from the central leader can be considered dominatedstructures. Pruning back into the flower buds of the 2-year-old wood during wintertime on Twig Aand Twig B will give a totally different growth reaction; the growth reaction will be strongest onTwig A.Central leader2 y1 yTwig A2 y1 yTwig BFLOWER BUD ORIENTATIONThe placement of a flower bud on afruiting branch determines the development.There is a clear superiority of flowerbuds on the upper side of the fruiting(1)(2)THE COMPACT FRUIT TREE, VOLUME 34, NUMBER 4, 2001 119

growth habits of the tree. These differencesin branch diameter should be taken intoaccount during the winter pruning. Thesebranches can be classified as dominant oras dominated structures and the responseof the same pruning cut will be totally differentwhen it is made in dominant twig orin dominated branch, even when thebranches have the same age (Fig. 1).EARLY PRODUCTIVITYFor intensive pear orchards early productivityis a must for economical reasonsas well as for natural growth control. Thefirst pears should be harvested in the secondyear after planting with productivityestimated at 3 to 5 kg/tree (6.6 to 11 lb/tree). Gibberellin treatments can help toimprove this early productivity on youngConference trees. In Table 3 some resultsare summarized with different gibberellintreatments applied during full bloom ontrees in their second season after planting.This trial was made on young Conferencetrees on Quince Adams in the secondyear after planting. The GA 3 treatment inthis trial was made as tablets of 10 g(0.022 lb) each containing 1 g active ingredientper tablet (0.0033 lb). The GA 4/7 was appliedas Regulex, containing 9 g/l GA 4/7(0.02 lb). For fruit set improvement, the GA 3treatment is clearly stronger than the GA 4/7 .The different forms of GA 4/7 have a comparablepositive effect on fruit set. For a fertilepear cultivar like Conference, it is not alwaysnecessary to take the strongest fruit set effect.Splitting up the total dose of GA 4/7 in twotreatments, one during full bloom on the 2-year-old wood and one during full bloomTABLE 3on the 1-year-old wood some days later, canbe interesting during variable climatologicalconditions. Also the combination of alow dose of GA 3 and half dose of GA 4/7looks promising. On young trees the risk fornegative effects on fruit size or on return tobloom is very limited but on adult trees riskshould be taken into account.The global result of these gibberellinapplications is different from year to yearwith sometimes substantial differences butin other years with no differences. The fruitset improvement is only one factor in thewhole series of phytotechnical measuresthat determines the final result.NUTRITIONMost of the Belgian pear orchards haveno possibilities for irrigation or fertigation.Nitrogen and potassium are two importantnutritional elements for pear growingin Belgium, nitrogen for an optimal fruitset and potassium for an optimal fruitquality. After the loss of chloormequat(CCC) as growth regulator there is a tendencyto reduce nitrogen partially or evencompletely in Belgian pear growing. Thiscould be negative for the normal fruit setcapacity of the flowers which need nitrogenavailable in the NO 3 form duringbloom and immediately afterwards duringthe process of flower drop and fruitletdrop. Postharvest applications of nitrogenare often used to improve the nitrogen reservelevel in the tree and to avoid vegetativegrowth reactions on the trees. Postharvestnitrogen can be applied by the roots oras a leaf nitrogen application with urea.Part of the nitrogen should always be givenFruit set improvement on young Conference pear trees with different gibberellin treatments (ns=nosignificance; *=significance of 95%; **=significance of 99%).% fruit set 2 yr wood after % fruit set 1 yr wood afterflower drop June drop flower drop June drop # pears/tree1. Untreated 18.4 8.7 25.2 11.5 33.62. GA 3 (10 tablets/ha) 35.3 ** 25.5 ** 32.8 ** 19.6 ** 44.0 ns3. GA 4/7 (1.2 l/ha) 23.7 ns 15.1 ns 23.4 ns 14.7 * 36.4 ns4. Promalin (0.6 l/ha) 22.2 ns 15.1 * 25.9 ns 14.6 ns 37.1 ns5. GA 3 (10 tabl.) + 27.1 * 18.1 ** 27.8 ns 20.5 ** 34.6 nsGA 4/7 (0.6 l/ha)6. GA 4/7 (2 x 0.6 l/ha) 24.9 ns 16.7 * 32.5 ** 20.1 ** 39.9 nssome weeks before bloom (20 to 30 kgN/ha; 17.8 to 26.7 lb/acre). This ensuresthat nitrogen will be available duringbloom for optimal fruit set. Early leafanalysis can give useful information on thenitrogen content during the floral andpostfloral period.CONCLUSIONPear growing in high density plantingsis possible with different training systemsbut there are important differences inlabor needed for each system. Planting materialfor intensive growing should be wellfeathered2-year-old trees with at least 6feathers. Information on flower bud qualityon different structures in the pear treecan help improve the regularity of theyield. The best flower bud quality on pearis found on the terminal flower buds onshort brindle shoots. Flower buds in terminalposition give higher fruit set percentagesthan in other positions. Pear treeshave an epitonic behavior, which meansthat the development of flower buds andshoots is better on the upper side of thebranches. The use of gibberellins is necessaryto guarantee the early productivity ofyoung pear trees. Nitrogen is important fora regular fruit set on young pear trees andshould be available during bloom and justafter bloom.REFERENCESBrunner, T. and I.K. Kecskes. 1990. Physiological fruittree training for intensive growing. Budapest:Akademiai Kiado.Demayer, L. and J.C. Deckers. 1984. Flower bud qualityin the pear cultivar Doyenné du Comice:1982–1983 trials. Acta Hort. 149:153–160.Rom, C.R. and B.H. Barritt. 1990. Spur developmentof Delicious apple as influenced by position,wood age, strain and pruning. HortScience25(12):1578–1581.Volz, R.K., E.W. Hewett and D.J. Wooley. 1992. Applefruit quality variation within the tree canopyat harvest. Postharvest Physiology Conference,California.*Research subsidized by the Ministry ofSmall Enterprises, Traders and Agriculture,Administration for Researchand Development120 INTERNATIONAL DWARF FRUIT TREE ASSOCIATION