Crop Protection from Permethrin Applied Aerially to Control Pale Western Cutworm (Lepidoptera: Noctuidae)

Abstract

Permethrin was aerially applied at 78 g (AI)/ha in two experiments to control pale western cutworm, Agrotis orthogonia Morrison, in wheat, Triticum aestivum (L.). Despite low wind and favorable thermal lapse conditions during application, residue analyses showed that only 55 and 78% of the permethrin was deposited on the soil. Spray coverage, as indicated by water-sensitive papers placed on stakes above the crop canopy, was 26 and 22 droplets per cm2. Three days after application, cutworm control was only 9 and 55%. This low initial control was attributed to the proportion of the cutworm population, 50 and 34%, that was molting and therefore inactive at the time of treatment. Mortality of these cutworms was delayed until they resumed feeding and became exposed to the permethrin residues. By 7d after application, cutworm control had increased to 81 and 84%. The treatments reduced the initial populations of 5.4 and 20 cutworms per m2 to 0.6 and 2.6 cutworms per m2, respectively. The remaining populations were well below the economic threshold of 5 cutworms per m2. Daily counts of plant stand in one experiment showed that after an initial overnight loss of 16%, the permethrin treatment gave considerable crop protection. After 7d, 70% of the plants remained in the treated plots compared with only 40% in the unsprayed check plots. The linear relationship, y = -2.6 x + 76 ( r 2 = 0.70), between plant stand remaining ( y ) and number of cutworms per m2 ( x ) was improved by using cumulative insect-days as the indicator of cutworm survival.