Identifying Integrated Pest Management Strategies for corn earworm, Helicoverpa zea, in Hemp

Abstract

Corn earworm, Helicoverpa zea (Lepidotera: Noctuidae), is a polyphagous insect species that feeds on the foliar, fruiting, and flowering structures of their host plants. In hemp (Cannabis sativa L.) corn earworm feeds on the flower buds which is the marketable portion of the plant. Managing this pest in hemp is challenging due to limited effective pest management tools and the complex regulatory measures surrounding chemical control. To address this issue, field trials and laboratory bioassays were conducted to evaluate the efficacy of insecticides against corn earworm. The field trials involved the application of biological insecticides registered for hemp and conventional standards used in other crops. Damage ratings, caterpillar counts, and harvest data were collected. Results from the field trials showed no significant difference in the effectiveness of insecticide treatments, but conventional insecticides were more effective than biological insecticides. In the laboratory bioassays, conventional insecticides were effective one day after insecticidal exposure, while the biological insecticides took on average four days to provide effective control. Two field experiments were conducted in 2022 to evaluate alternative control strategies. The first experiment utilized a sweet corn trap crop to reduce corn earworm damage in hemp. Different sweet corn planting dates were tested, and the trap crop showed potential for reducing damage to hemp. The second experiment assessed varietal preferences of corn earworm in four hemp varieties. Significant differences were observed in plant measurements, cannabinoid concentrations, caterpillar numbers, and damage ratings. These findings highlight the importance of considering cultural control strategies and varietal selection to manage corn earworm in hemp effectively.