Table 3. Average number of insecticide and miticide treatments per block. 



Insecticide 



Miticide 



Year 



Block 



Pre-bloom April to Early June April to Early June 

 oil early June onward early June onward 



1987 



1988 



1989 



3.8 

 4.0 



3.2 

 3.2 



3.8 

 3.8 



1.3* 

 2.7 



0.8* 

 2.0 



0.3* 

 1.3 



•Treatments applied only to perimeter apple trees - not to block interior. 



ferences between blocks in levels of apple aphids or 

 aphid predators. 



With respect to frequency of insecticide and miti- 

 cide use, from April to early June, on average over the 

 3years, both first- and second-stage blocks received 1.5 

 oil sprays, 3.6 insecticide sprays, and miticide sprays 

 (Table 3). Thereafter until harvest, first-stage blocks 

 received on average 3.0 insecticide sprays and 2.0 miti- 

 cide sprays. Second-stage blocks received (on perime- 

 ter trees only) an average of 2.8 insecticide and 0.8 

 miticide sprays (Table 3). Average annual per acre 

 costs of oil, insecticide, and miticide treatments over 

 the 3 years were about $194 for the first-stage blocks, 

 versus about $110 for the second-stage blocks. When 

 determining cost of treating second-stage blocks from 

 early June onward, we estimated perimeter trees as 

 comprising about 25% of an assumed rectangular 2- 

 acre block of M.7 trees (225 trees per block). 



Conclusions 



In conclusion, we generally are pleased with the 

 results of this perimeter-row spraying approach to 

 achieving the second-stage apple IPM aim of keeping 

 the interior of apple orchard blocks free of insecticide 

 and miticide sprays after early June. Fruit injury by 

 codling moths, lesser appleworms, and leafrollers was 

 absent or in low amount. Foliar pests such as leafhop- 

 pers, aphids, and leafminers were essentially no more 

 abundant in second-stage than first-stage blocks. 

 Annual insect and mite control cost only about 60% as 

 much in second-stage as in first-stage blocks. 



We are somewhat cautious, however, with respect 



to long-term effective control of apple maggot and 

 mites using this approach. In 1989, apple maggot 

 injury was considerably more pronounced than in 1987 

 or 1988 in second-stage blocks or than in any year in 

 first-stage blocks. In contrast, apple maggot injury 

 progressively declined from year to year under the 

 second-stage IPM approach of using odor-baited visual 

 traps on perimeter apple trees to capture maggot flies 

 (see preceding article). The reason for the sharply 

 increased average level of maggot injury in 1989 in 

 perimeter-sprayed blocks is unclear, but could reflect 

 greater buildup of apple maggot flies within orchards 

 as a consequence of greater fruit drop in the absence of 

 Alar™. If so, then a perimeter-row spray approach to 

 controlling apple maggot maybe reliable only in blocks 

 where drops of early- and mid-ripening cultivars are 

 picked up at harvest to prevent maggots maturing in 

 them. With regard to mites, in no year did the average 

 ratio of pest mites to predator mites in perimeter- 

 sprayed second-stage blocks reach as low as 5 to 1, 

 which is considered favorable for effective biological 

 suppression of pest mites. The ratio always exceeded 7 

 to 1 and was never as favorable as in second-stage 

 blocks receiving apple maggot traps rather than sum- 

 mer insecticide treatment on perimeter apple trees 

 (see preceding article). Perhaps a substantial propor- 

 tion of predatory mites is immigrating on wind into 

 orchards from plants surrounding the orchard and 

 perhaps these predators are affected by pesticide treat- 

 ment of border rows. 



As a final word, we now believe that we can recom- 

 mend with reasonable confidence the value of a pe- 

 rimeter-row spray approach as a transitional step 



Fruit Notes, Winter, 1990 



11 



