great enough to maintain mites below injurious quired treatment with Dimilin™ against sec- 

 levels in some second-level blocks. Not until late ond-generation leafminers. Leafminer popula- 

 August did the ratio of pest mites to Amblysieus tion levels throughout the summer confirmed 

 fallacis predators drop below 5:1, indicating our previous conclusion that application of 

 that there was a probability for biocontrol. Mi- Dimilin™ against the overwintering generation 

 ticide was recommended and applied early in of leafminer adults, when indicated by trap 

 the summer in several second-level blocks to captures, is the most effective and least invasive 

 prevent mite outbreaks (Table 2). Further technique for their control. In 1991, permission 

 study is needed of additional factors that can to use Dimilin™ in second-level blocks was not 

 contribute to predator buildup in the absence of granted until it was too late to treat the overwin- 

 post-May insecticide treatment. tering generation. Treatment of second-genera- 



Both potato and white apple leafhopper tion adults and eggs is more difficult to time, and 

 population levels on terminals were slightly, but was not successful in one of the second- level 

 not significantly, higher over the course of the blocks. Nonetheless, the season-long average 

 season in second-level than in first-level blocks number of mines on 100 leaves was slightly, but 

 (Table 6). White apple leafhopper outbreaks not significantly, lower in second-level than in 

 occurred in two full second-level blocks, result- first-level blocks (26 vs. 33) (Table 6). Treat- 

 ing in 33% injured fruit in one block. Further ment with Dimilin™ is preferable to use of other 

 examination of the patterns of leafhopper materials which are harsher on beneficial in- 

 buildup is needed in order to better predict sects and mites. Several growers chose not to 

 outbreaks such as these. treat leafminers in their first-level blocks, where 



Early season trap captures indicated that all Dimilin™ could not be applied. Consequently, 



but one of the six full second-level blocks re- dosage equivalents of pesticide applied against 



Table 6. Foliar insect pest population and injury levels in second-level vs. first-level IPM 

 blocks. 12 



PLH WALH 



Type of block PLH 3 injury 4 WALH 3 injury 5 ABLM 6 WAA 7 GAA 7 GAAP 7 



Full 



second-level 8.9a 16.6a 4.1a 4.2a 25.5 a 20.7a 72.8 a 68.7 a 



First-level 6.8a 11.2a 1.0a 1.1a 33.1a 17.0a 70.2 a 58.9 a 



Transitional 



second-level 5.8 a 7.0 a 5.7a 5.8 a 38.9 a 13.7 a 47.5 a 29.5 a 



First-level 1.6 a 12.2 a 1.5a 0.3 a 64.6 a 17.5 a 37.9 a 18.2 a 



•PLH = potato leafhopper; WALH = white apple leafhopper; ABLM = apple blotch 



leafminer; WAA = wooly apple aphid; GAA = green apple aphid; GAAP = green apple aphid 



predators: cecidomyiids and syrphids. 



2 Means in each couplet in each column followed by a different letter are significantly 



different at odds of 19:1. 



Percentage of terminals and watersprouts examined. 



4 Percentage of terminals examined. 



Percentage of fruit examined at harvest. 



6 Average number of mines on 100 leaves. 



Percentage of watersprouts examined. 



10 Fruit Notes, Spring, 1992 



