Walnut Husk Fly Control with Low-Toxicity Insecticides, 1997

The study was conducted on mature ‘Payne’ walnut trees in a commercial orchard near Hollister, Calif. Five treatments were replicated four times in a RCB design. Each replicate consisted of an individual tree. Treatments were applied with a backpack air-blast sprayer with a finished spray volume of 100 gpa (1.11 gal/tree). The first application was initiated one week after the appearance of walnut WHF ovipositional punctures and a second application was applied two weeks after the first application. Control was evaluated by visually examining 25 walnuts per replicate weekly from 26 Jun through 31 Jul. The walnuts were inspected for ovipositional punctures and larval feeding. The larval feeding was classified on a scale of 0 to 5 where: 0 = no larval feeding or husk discoloration, 1 = slight larval feeding with very little husk discoloration, 2 = slight larval feeding with husk discoloration about 1 cm2 in size, 3 = moderate larval feeding with husk discoloration about 2 cm2 in size, 4 = heavy larval feeding with over ½ of the husk discolored, 5 = heavy larval feeding with entire husk discolored and/or larval emergence from the husks. Additional 25 walnuts per replicate were dissected on 17 and 31 Jul. The walnuts were classified as nuts with or without eggs and/or first, second or third instar larvae.