Effects of aerial spray volume, coverage, and abamectin on Scirtothrips perseae (Thysanoptera : Thripidae)

Helicopter applications using abamectin indifferent spray volumes were made against Scirtothrips perseae Nakahara in Ventura County, CA. On small (2.2 m tall) trees, spray coverage on water-sensitive papers was 24-48% and 43- 97% for 468 and 935 liter/ha volume treatments, respectively. On large (6.2 -8.1 in tall) trees, spray coverage was lower and quite variable, from I to 28% and 10 to 70% for 468 and 935 liter/ha treatments, respectively. On sm all trees, 468, 701, and 935 liter/ ba with a high abamectin rate (26 g [AI ]/ha) were equally effective against larvae from 13 to 27 d after treatment (DAT). On medium (4.2 m tall) trees, 468 and 935 liter/ha with the high ra te were equally effective from 23 to 113 DAT. On large (6.5-8.1 m tall) tre es, 468 and 935 liter/ha with a low abamectin rate (13 g [AI]/ha) were inef fective in three tests. In a fourth large (6.8 m tall) tree test, 468 and 9 35 liter/ha with the high rate were effective at 3 and 37 DAT. In a fifth l arge (6.2 m tall) tree test, 468-1,403 liter/ha with the high and 935 liter /ha with the low rate were equally effective 2-22 DAT. After all effective treatments, thrips numbers were lower than in controls for 1-3 mo. However, stable and highest reductions in populations were sometimes delayed until 20-23 DAT even when coverage was high. The variability in spray coverage on the lower levels of large trees and the delayed effect may explain inconsi stencies in the reporting of or in actual aerial application results.