Rainfall influences performance of insecticides on the codling moth (Lepidoptera: Tortricidae) in apples

Semi-field studies were used to evaluate the effects of rainfall and field ageing on the performance of insecticides from six different chemical classes used to control the codling moth (Lepidoptera: Tortricidae). All insecticides were significantly more toxic to codling moth larvae than the untreated control, although seven-day field ageing reduced control for several compounds. Simulated rainfall events of 2.54 and 12.7 mm did not have negative effects on the performance of the insecticides. Simulated rainfall events of 50.8 mm of rainfall resulted in significant reductions of efficacy for thiacloprid and spinetoram. Residue profiles of apple leaves and fruit provided evidence for wash-off ranging from 13% to 93%, with patterns varying by compound, plant substrate, and rainfall level. This study will help apple growers make informed decisions on when reapplications of insecticides are needed in the field with the aim of improving integrated pest management.