Table 2.Average percent leaves (or terminals) harboring foliar pests or beneficial natural enemies.*' 



Year 



Block 



ERM 



TSM 



AF YM 



Ratio of 



pest to 



predatory 



mites 



WAA WAL PL ABLM GAM GAAP 



1987 

 1988 

 1989 



Second-stage 



First-stage 



Second-stage 



First-stage 



Second-stage 



First-stage 



24 

 16 

 12 

 10 

 24 

 23 



1.2 

 0.3 

 0.3 

 0.5 

 3.6 

 2.5 



0.1 

 0.0 

 0.1 

 0.1 

 0.1 

 0.0 



19:1 

 48:1 

 30:1 

 17:1 

 7:1 

 9:1 



5 

 5 

 5 

 5 

 10 

 8 





 1 



8 

 6 

 1 



1 



9 

 10 

 2 

 2 

 1 

 1 



5 

 4 

 4 

 6 

 6 

 6 



31 

 23 

 59 

 55 



11 



8 



47 



50 



*400 leaves (or terminals) sampled per block during June, July, August, and September. 

 "ERA = European red mites; TSM = two spotted mites; AF = predatory Amblyseius fallacis; YM = preda- 

 tory yellow mites; WAA = woolly apple aphids; WAL = white apple leafhopper; PL = potato leafhopper; 

 ABLM = apple blotch leafminer; GAA = green apple aphid; GAAP = green apple aphid predators: 

 cecidomyiids and syrphids. 



their principal natural enemies. Each year pest mites 

 averaged greater in abundance in second-stage than 

 first-stage IPM blocks. The difference was substantial 

 in 1987 (50% greater pest mites in second stage blocks) 

 but narrowed to only 4% greater in 1989. Predatory 

 Amblyseius fallacis mites averaged greater in second- 

 stage than first stage blocks in 1987 and 1989 but the 

 reverse was true in 1988. Predatory yellow mites were 

 very few in number in any block in any year. The 

 overall ratio of pest to predatory mites was unfavorable 



for effective biological control in either type of block in 

 1987 and 1988 (never more favorable than 17 to 1) but 

 was favorable for moderately effective biological con- 

 trol in both types of blocks in 1989 (7 or 9 to 1). 



Data in Table 2 also show levels of other foliar pests 

 and natural enemies. There was very little or no 

 difference between block types in any year in popula- 

 tion levels of woolly apple aphids, white apple leafhop- 

 pers, potato leafhoppers, or apple blotch leafminers. 

 Likewise, there were no consistent or appreciable dif- 



10 



Fruit Notes, Winter, 1990 



