As a growing industry in the United States, hemp (Cannabis sativa with <0.3% of delta-9-tetrahydrocannabinol) has exponentially increased, not only in its number of licensed acres (approximately 500,000 across 45 states), but also in its capacity to diversify into at least 25,000 commercial products. Such growth comes along with inherent issues related to pest management. There are at least 270 pest species that have been reported attacking hemp around the world. However, many years of prohibiting hemp production have restrained research-based studies, thus direct injury to plants and resulting economic losses associated with these pests are poorly understood. Among the most common pests attacking hemp in Kentucky, budworms (e.g., corn earworm and tobacco budworm) are known to attack hemp grown for CBD.
Corn Earworm
Corn earworm Helicoverpa zea (Lepidoptera: Noctuidae) populations can reach up to 50 caterpillars per plant (tallied last year in commercial fields in Caldwell County) and is a rising concern among hemp growers in Colorado, Illinois, Indiana, Kentucky, Nevada, North Carolina, Tennessee, Vermont, Virginia, and Wisconsin. Corn earworm caterpillar displays a varied color patterns ranging from light green to dark brown.
Yellow-striped Armyworm
Although, the yellow-striped armyworm Spodoptera ornithogalli (Lepidoptera: Noctuidae) is a common pest in the eastern United States, it has never been documented to cause economic damage on hemp. The larvae of this species are recognized by the presence of well-marked yellow bands across the lateral sides of the body and an inverted "Y" marking on the head capsule.
During weekly inspections to hemp plots at the UK Research and Education Center at Princeton and a commercial farm in August, corn earworm and yellow-striped armyworm were found feeding on hemp plants. Although, corn earworm can produce some damage to the foliage, the most important injury to hemp occurs when the larva feeds on the flower buds. However, the yellow-striped armyworm is mostly found feeding on the foliage.
Management
These two species have not been found in large numbers yet, but their populations will eventually increase toward the beginning to end of September. Hemp growers should keep inspecting their fields and consult with an Extension specialist before considering spraying. Conventional insecticides are not registered to control these pests, but organic insecticides such as Bacillus thuringiensis, pyrethrin, or neem-based products may be used if they are registered in Kentucky. Special attention should be paid to the populations of corn earworm attacking flower buds that may affect CBD production.
More Information
- Falcon-Brindis, A., J. O. Stireman III, Z. J. Viloria, R. T. Villanueva. 2022. Parasitism of Corn Earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by Tachinid Flies in Cultivated Hemp. Insects, 13(6): 519.
- ENTFACT-321: Yellowstriped Armyworm. UK Extension. https://entomology.ca.uky.edu/ef321
- Corn Earworm Outbreaks in Industrial Hemp in Kentucky: September -- 2019. Kentucky Pest News. https://bit.ly/3CLYMm3
Categories: Illinois, Crops, Indiana, Crops, Kentucky, Crops, Corn, South Dakota, Crops