Feeding Behavior and Influence of Hemp Varieties and Fertilization Rates on Damage Caused by Corn Earworm, Helicoverpa zea

Production of industrial hemp, Cannabis sativa L., has increased tremendously in the U.S. after its legalization through the Agricultural Improvement Act of 2018, known as the 2018 Farm Bill, which allowed commercial hemp production. By grower number, in 2020, Tennessee was the nation’s largest hemp program with over 1,800 producers licensed to grow up to 6,500 hectares (16,000 acres) according to the Tennessee Department of Agriculture. Though fiber and seed have a role in the industry, most growers (ca. 98%) concentrate on cannabidiol production because of the expected higher cash value potential per hectare. Introducing hemp as a monocrop system in this temperate region while researchers scramble to provide pest management strategies seems to be brewing a perfect storm for hemp. This emerging industry has been negatively impacted by larvae of corn earworm, Helicoverpa zea (Boddie), which feed on developing inflorescences. Unfortunately, few synthetic chemical pesticides are labeled for use on hemp which provides a unique opportunity to investigate alternative control methods.

A two-year study designed to characterize and evaluate the impact of corn earworm on hemp was initiated in eastern and western Tennessee by examining varietal characteristics, agronomic practices, and larval damage levels. The primary research goals of this project were to: 1) characterize the feeding behavior of corn earworm on hemp and assess the fitness of corn earworm reared on two varieties of hemp, 2) determine the impact of corn earworm on five varieties of hemp, and 3) determine the influence of hemp variety and fertilization practices on corn earworm. The results of this study have revealed that variety and plant maturity are highly correlated to larval damage (p≤0.05). No correlation between fertilizer or cannabinoid concentrations and larval damage was found (p>0.05). Findings from this research allow hemp growers to make informed agronomic decisions before planting to improve hemp production in Tennessee. Further research on floral processing requirements, pesticide efficacy, terpene attractance to corn earworm moths, parasitoid species as a means of biological control, and varietal selection will lessen the impact of corn earworm larval damage on hemp.