still active or at least had not begun to shrivel. 

 N3Tnphs in the petal-fall to first-cover sample 

 appeared to have been trapped early in the 

 period and were inactive, darkened, and had 

 begun to shrivel. Eleven trees that had the tape 

 traps removed at petal fall were re-banded to 

 investigate further the timing of migration. In 

 all eleven trees, those that had njmiphs trapped 

 on bands prior to petal fall also had nymphs 

 after petal fall, and those that did not have 

 nymphs trapped on bands did not have any after 

 petal fall. From these results, I conclude that 

 the majority of root migration takes place within 

 a few days before and after petal fall. All three 

 samples, therefore, that included petal fall were 

 pooled and analyzed as one sample, because the 

 presence or absence of migrating nymphs, not 

 the nvmiber of nymphs, was used as the predic- 

 tor variable. 



From traps on the 75 trees in the pooled 

 sample, fifteen (20%) had first-instar woolly 

 apple aphid nymphs (the median number of 

 nymphs per trap was 8 but ranged fi-om 1 to 

 2883). Trees that had traps with migrating 

 nymphs had a larger number of root colonies 

 and a more severe root infestation than trees 

 without migrating njrmphs (Table 2). For trees 

 on which nymphs were trapped, 80% had root 

 colonies, and 73% had root gall infestation rat- 



ings greater than 0.21. For trees without 

 trapped nymphs, only 20% had root colonies and 

 only 22% had root gall infestations greater than 

 0.21. F\ui,her, the mean nimiber of root colonies 

 and root gall infestations were 4.1 and 0.3 for 

 trees with trapped nymphs, respectively, and 

 0.5 and 0.2 for trees without trapped njmaphs, 

 respectively. 



Conclusions 



The presence of n5Tnphs migrating up the 

 tree fi*om roots during petal fall is an indication 

 of the size of the woolly apple aphid population 

 on the roots of that tree. Masking tape with a 

 Tangle-trap^" barrier was successful in trap- 

 ping these migrating njmiphs. By sampling an 

 orchard, one can estimate the number of trees 

 that have serious woolly apple aphid root infes- 

 tations by comparing the number of trees with 

 migrating nymphs versus those without. One 

 could also identify portions of an orchard that 

 may have a woolly apple aphid problem and 

 take suitable action: apply insecticides against 

 above-ground feeding aphids which would even- 

 tually lower root-feeding populations, delay re- 

 planting or plant other crops for a year or two, or 

 apply insect parasitic nematodes, which is a 

 promising potential control method (Brown et 

 al., 1992). 



8 



Fruit Notes, Fall, 1993 



