Impact of Western Bean Cutworm (Lepidoptera: Noctuidae) Infestation and Insecticide Treatments on Damage and Marketable Yield of Michigan Dry Beans.

Abstract

The western bean cutworm, Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), recently expanded its range from the western United States into the Great Lakes region of the United States and Canada, threatening eastern dry bean production. Our objectives were to better understand the relationship between cutworm infestation and damage in dry beans, and to determine the best method and timing of insecticide application to reduce pick. Infesting with at least one egg mass per 1.5 m, or as few as two larvae per 0.3 m, of row resulted in significantly more pod damage and pick than in uninfested plots. By 14 d after hatch, larvae were no longer on plants during the daytime; direct observations revealed that fifth instars climbed plants to feed between 2100 and 0600 hours, illustrating the impractically of using larval counts to make management decisions. There was a strong linear relationship between pod damage and percent pick, making scouting for pod damage a viable alternative to egg or larval scouting. Aldicarb soil insecticide or thiamethoxam-treated seed did not reduce cutworm damage. Instead, plots treated with these insecticides had significantly more pick than control plots, perhaps related to increased canopy growth or fewer natural enemies. The pyrethroid λ-cyhalothrin provided excellent control of cutworm when sprayed up to 18 d after infestation. Pick was similar among plots sprayed once up to 18 d after infestation or sprayed four separate times. In a field study, λ-cyhalothrin residue on field-treated foliage was 100% effective at controlling caterpillars up to 14 d after application.