Spray Droplet Size in the Control of Spruce Budworm, Boll Weevil, Bollworm, and Cabbage Looper1

The fluorescent particle spray droplet tracer method was used under field conditions to determine the size and number of spray droplets which impinged on spruce budworm, Choristoneura fumiterana (Clemens), in a Montana mountain forest and on the boll weevil. Anthonomus grandis Boheman; bollworm, Heliothis zea (Boddie); and the cabbage looper, Trichoplusia ni (Hubner); in a Georgia cotton field. The data obtained reflect the physical, mathematical, biological and meteorological factors which determine transport to and impingement of the insecticide sprays on these insects in their widely diverse environments. A total of 101,495 spray droplets was identified by size and counted on 1324 insects. Eight droplets were identified in the 101-120µ diameter range. A total of 99,383 droplets (98%) was in the 21-30µ range; droplets less than 50µ diameter constituted 99.7% of the total. The data show that the maximum diameter for efficient insecticide spray droplets is less than 50µ. There is no evidence that spray droplets larger than 100µ have any substantial efficiency in delivery of insecticide to these insects.