The Effects of Summer Pruning on Insect 

 and Mite Populations in Apple Trees 



Susan L. Butkewich, Ronald J. Prokopy, and William Pyne 

 Department of Entomology, University of Massachusetts 



Wesley R. Autio and Duane W. Greene 



Department of Plant & Soil Sciences, University of Massachusetts 



Summer pruning is one way to reduce setbacks in 

 apple production caused by the elimination of Alar^"^ 

 from a grower's spray program. Without Alar, fruit 

 may drop before they become red enough to yield a high 

 marketvalue. In previousissuesofFrwi7iVo/es [52(3);7- 

 8, 53(2):1, 53(3): 1-2] the benefits derived from summer 

 pruning of Mcintosh trees were illustrated. An in- 

 crease in light penetration into the tree from summer 

 pruning resulted in 1) earlier coloring of fruit, 2) a 

 higher percentage of fruit making the U. S. Extra 

 Fancy grade, 3) earlier harvesting of fruit, and 4) 

 production of more fruit with a potential for long term 

 storage. 



Little is known about the effects of summer prun- 

 ing on apple arthropod pests and predators. Pruning of 

 vegetative sprouts may remove a resource for pests 

 that prefer to feed on young succulent tissue (e.g., 

 green apple aphid and spirea aphid), but wound exu- 

 date from pruning cuts may offer direct nutrient bene- 

 fits to pests like wooly apple aphid. Summer pruning 

 may also trigger a change in the level of tree nutrients 

 or defense compounds, and subsequently influence 

 phytophagous arthropod populations this way. 



Two pruning experiments were conducted in 1988 

 on M.7 Mcintosh trees at the University of Massachu- 

 setts Horticultural Research Center, Belchertown. These 

 studies were undertaken initially to determine the 

 effect of summer pruning on fruit production. How- 

 ever, data on fruit yield and quality will be reported in 

 a future issue of Fruit Notes. Here, only data on arthro- 

 pod pest and predator levels are reported. 



On August 26, 10 fruit cluster leaves and 10 non- 

 cluster leaves were sampled from the interior of each 

 tree at about head height. Within a cluster, the third to 

 the fifth leaf out was sampled. Non-cluster leaves were 

 picked from the interior part of a branch (not the 

 branch terminal) and were equivalent in size to cluster 

 leaves. The underside midrib area of each leaf was 

 evaluated for presence or abscence of European red 

 mites (ERM) and two-spotted spider mites (TSSM), 

 and also for presence or absence of the predatory mites 



Amblyseius fallacis (AF) and Zetzelia mali (ZM). These 

 leaves were also evaluated for white apple leafhopper 

 (WALH) damage and apple blotch leafminer (ABLM) 

 damage (sap and tissue feeders). In addition, 10 prun- 

 ing cuts on the tree interior were sampled for the 

 presence of wooly apple aphid (WAA). In control (non- 

 pruned) trees, 10 pruning cuts from the previous year 

 were examined. 



Experiment 1 was aimed at determining benefits of 

 summer pruning at various times after June. Three 

 rows of trees were randomly divided to accommodate 8 

 replications of 6 treatments. The treatments consisted 

 of trees pruned on July 1, July 15, August 1, August 15, 

 and September 1 and a control tree that was not 

 pruned. 



Experiment 2 was conducted to determine effects 

 of summer pruning in combination with stop-drop 

 applications. In the same rows as Experiment 1, addi- 

 tional trees were chosen to provide 7 replications of 

 these treatments: 1) summer pruning, 2) summer 

 pruning plus NAA, 3) summer pruning plus Alar, 4) 

 NAA, 5) Alar, and 6) a control that received no treat- 

 ment. In this experiment all summer pruning occurred 

 on August 1 . Alar was applied on July 15. NAA was ap- 

 plied on September 18, after the first harvest (Septem- 

 ber 16). Note that NAA was applied after the arthropod 

 sample date. Data from treatments 2 and 4 thus will be 

 excluded. 



Results from both experiments revealed that popu- 

 lation levels of WALH, TSSM, and the predator mites 

 ZM and AF were extremely low and not significantly 

 different among treatments. Low populations of ZM 

 and AF are typical of orchards where predator-harsh 

 pesticides have been used. Populations of TSSM are 

 often low in situations where ERM may have outcom- 

 peted them. 



Population levels of other insects and mites sur- 

 veyed in Experiment 1 varied among treatments (Table 

 1). On most sampling dates, more ERM were found on 

 fruit cluster leaves than on non-cluster leaves. There 

 were no trends that may have suggested that pruning 



Fruit Notes, Spring, 1989 



