By Marguerite Bolt and Amanda Skidmore, Ph.D.
Hemp (Cannabis sativa) is a novel crop recently legalized for commercial production in the United States via the 2018 Farm Bill. Reasons for hemp production can be separated into three different categories: grain, fiber, and the compound cannabidiol (CBD). Each production system needs to be evaluated to decide which pests will require management strategies to keep damage below economic thresholds.
In particular, one important need is to determine if insect feeding can increase tetrahydrocannabinol (THC) production, which is a very real concern, because the THC content in a hemp crop must remain below a threshold set at 0.3 percent on a dry-weight basis.
As expected with a new crop, gaps exist in the literature surrounding all aspects of hemp production. Our colleagues in this field recognized the need for an updated synopsis of arthropod pests that have been observed on hemp during various research trials. A group led by Whitney Cranshaw, Ph.D., professor and extension specialist at Colorado State University, with colleagues at CSU, Virginia Tech, the University of Vermont, and the University of Tennessee, have assembled such a profile, published last week in the open-access Journal of Integrated Pest Management.
Integrated pest management (IPM) plans for pests of hemp are still being developed because arthropod pests are still being identified and described. Meanwhile, for insects already recognized as hemp pests, research on cultural, mechanical, and biological control strategies are still needed. Not all the arthropods in the hemp agroecosystem are causing apparent economic impacts, and therefore many would not require any management considerations. Corn earworm (Helicoverpa zea), Eurasian hemp borer (Grapholita delineana), hemp russet mite (Aculops cannibicola), and cannabis aphid (Phorodon cannabis) are pests that can cause economic loss for growers in some regions of the U.S. Pest management options include natural enemies, removing volunteer hemp plants, and rotating hemp with other crops. Some states have allowed the use of biopesticides (such as Bacillus thuringiensis var. aizawi or the Helicoverpa armigera nucleopolyhedrovirus), but growers should review their state’s regulatory rules to determine if this is a permissible option.
However, until repeated economic-loss-valuation studies are conducted and economic thresholds and injury levels are developed, IPM recommendations for hemp pests are still in their infancy. This article in JIPM is important for the scientific community to gain an understanding of the current knowledge of hemp agroecosystem research.
The long gap in large-scale industrial hemp production followed by a surge in production over the last five years has resulted in a lack of knowledge that puts hemp growers in a difficult position when developing new pest management practices. Although some states have a list of allowable pesticides for use in hemp, currently no pesticides are broadly labeled for hemp pests in the U.S. Thus, a unique opportunity exists to focus on cultural, mechanical, and biological control methods as pest pressure increases, which is especially important for hemp that is grown for consumable and medical use (specifically hemp oil and grain cultivars and CBD cultivars).