15. 



and miticide sprays on an every middle basis, which resulted in 

 somewhat higher than expected material and application costs. 



' Nevertheless growers utilizing alternate middle spraying 

 realized an average net benefit of $76.35 per acre in 1980. 



Summary of 5-year trends in alternate vs. every middle blocks . 



Overall, during the period 1976-1980, average percent injury 

 at harvest from insects was virtually identical in alternate vs. 

 every middle treatment blocks (Table 3) . 



Table 3. Average percent of insect injury to fruit at harvest 



and percent infestation with aphids and mites in four alternate 

 middle vs. every middle commercial orchard blocks, 1976-1980. 



Insect Every middle Alternate middle 



Tarnished plant bug 1.6 1.4 



Plum curculio 0.2 0.1 



San Jose scale 0.1 0.1 



Apple maggot fly 0.1 0.1 



European apple sawfly 0.2 0.2 



Green fruitworm 0.1 0.1 



Codling moth 0.1 0.0 



Other 0.0 0. 1 



Total percent insect injury 2.4 2.1 



% leaves with aphids 7.8 8.6 



% leaves with mites 8.8 (2.0)^ 11.2 (0.7)^ 



- 



1980 data in ( ) = no. mites per leaf. 



Specifically, while it is evident that tarnished plant bug is 

 the single most damaging pest in alternate and every middle blocks, 

 all the major fruit damaging insect pests appear to be equally 

 amenable to control using either alternate middle or every middle 

 spray techniques. 



Table 3 also shows the average percent of leaves infested with 

 aphids and mites in alternate vs. every middle blocks for the per- 

 iod 1976-1980. During this period aphid populations were slightly 

 higher in the alternate middle blocks. However, there was no sign- 

 ificant fruit injury from aphid honeydew or sooty mold growth in 

 either block, indicating that aphid infestations were below economic 

 injury levels and would not justify the cost of additional spray 

 applications (data not shown) . 



