Insecticides to Control Hemp Pests & Bolster Yield

Hemp ( Cannabis sativa) is a highly profitable crop that can be used for production of fiber, seed, oil and food. Like other crops, hemp production can be negatively affected by several pests, including insects, diseases and weeds. Unlike other crops, there are few pesticides labeled for hemp because the Environmental Protection Agency (EPA) has only recently permitted the registration of products after the U.S. federal government recognized hemp as a crop. This document lists and describes the insects and insecticides that are related to hemp production.

Insect Pests

Insect pests are one of the greatest challenges to agricultural producers because they have the potential to reduce or destroy yields. Identification of insect pests is important for a successful integrated pest management (IPM) program. Encountering non-pest insects is highly probable, because less than 3% of insects are considered pests. Misidentifying or treating a non-pest organism as a pest may cause a loss of time and money and increase unnecessary exposure to pesticides. Information about insect biology can be used to improve efficacy of IPM programs by choosing sufficient scouting and management methods. This information includes a wide range of factors, such as movement, feeding, reproduction, dispersal, host, diapause (dormancy) and various responses to environmental conditions, like temperature and humidity.

The following are insect pests that have been reported feeding on hemp:

Several caterpillar species have been observed attacking hemp. Corn earworm (Helicoverpa zea) can cause significant damage, particularly to hemp grown for production of large buds to extract CBD or other pharmaceutical compounds. Potential damage to fiber or seed producing cultivars is likely to be minimal. Corn earworms tunnel into buds and developing seeds. Corn earworms also are known as tomato fruitworms or bollworms. Color of the corn earworm caterpillars ranges from pale brown to nearly black, various shades of green, or even reddish tones. They will usually move into hemp in late summer with peak injury occurring after plants begin to flower during late August and September.

The Eurasian hemp borer (Grapholita delineana) also attacks hemp and has the potential to be a significant pest of hemp. However, this pest has not been reported in West Virginia. Caterpillars are quite small, reaching a maximum size of about 6 to 8 millimeters, and tunnel into stems and buds. They are noticed during harvest or when they get dislodged from plants during drying.

The beet webworm (Loxostege sticticalis) also can feed on hemp, but its damage is usually minor. Unlike corn earworms, beet webworm appears to limit most feeding to leaves. Caterpillars reach moderately a large size when full grown (¾ inch) and are generally green marked with striping and white spots that have a black center. Caterpillars are typically found feeding amongst emerging leaves and around buds, usually within some loose silken webbing that produces a shelter for the insect. Adults can be found from June to September. Yellow woollybears, saltmarsh caterpillars, variegated cutworms and beet armyworms are other caterpillar species that have been detected feeding on hemp, but their damage is likely to be minimal.

Several hemipterans (true bugs) also feed on hemp. Hemipterans use their sucking and piercing mouthparts to extract plant sap. For example, aphids are hemipterans that feed on hemp. When a high number of aphids are present, they can reduce plant vigor, resulting in slowed growth, wilting and leaf yellowing. In addition, several aphid species have the potential to transmit diseases, which can indirectly produce serious damage. Rice root aphid (Rhopalosiphum rufiabdominalis), cannabis aphid (Phorodon cannabis), green peach aphid (Myzus persicae), cotton/melon aphid (Aphis gossypii) and bean aphid (Aphis fabae) have been reported feeding on hemp.

Beet (Neoalitursus tenellus) and potato leafhopper (Emposaca fabae) also have the potential to cause significant yield loss to hemp. Feeding damage of potato leafhoppers disrupts the movement of nutrients and sugars accumulated in the leaves, resulting in “hopperburn” symptoms. In contrast, beet leafhoppers can transmit the disease beet curly top. Although, beet leafhoppers have been found in few hemp field surveys. 

Tarnished plant bug (Lygus lineolaris) and other Lygus bugs can became problematic in hemp being grown as an oilseed crop. Lygus bug is the name given to a group of plant bugs in the genus Lygus that are very commonly found in crops, gardens and natural areas of West Virginia. Damage by Lygus bugs includes distortion of new growth, flower abortion and deformities of seeds. Damage caused by stinkbugs (Pentatomidae: hemipteran) is likely to be minimal. Red-shouldered (Thyanta custator), conchuaela (Chlorochroa ligata) and Say’s (C. sayi) are some stink bug species reported feeding on hemp.

Spotted cucumber beetle (Diabrotica undecimpunctata) have been consistently found in hemp field surveys. This beetle is also known as southern corn rootworm. Although spotted cucumber beetle is commonly found in West Virginia, it tends to be more problematic in the south, attacking cucurbit plants, such as cantaloupe and cucumbers. It causes damage by feeding on roots, seedlings, flowers and foliage. Similar to some hemipterans, spotted cucumber beetle also can transmit pathogens that cause diseases, such as bacterial wilt of cucurbit. 

Thrips have been observed in indoor and outdoor grown hemp. Thrips feeding can damage leaves and shoots, and they have the potential to be vectors of viruses. Onion thrips (Thrips tabaci) and western flower thrips (Frankliniella occidentalis) have been reported feeding on hemp. Thrips are more problematic in settings with a regulated climate, such as greenhouses and high tunnels, because they protect thrips from natural enemies and environmental conditions.

Last, non-insect pests, such as mites, have also been reported attacking hemp. Similar to thrips, they can feed on indoor and outdoor grown hemp, but they tend to be more problematic in greenhouses and high tunnels. Both two spotted (Tetranychus urticae) and hemp russet mites (Aculops cannibicola) have been reported.

Insecticides

IPM combines various approaches of pest control to develop programs that are both effective and environmentally responsible based on inspection, pest identification, monitoring, control strategies and evaluation. The approaches used in IPM programs can be categorized as cultural, mechanical, biological and chemical control. Chemical control uses pesticides to kill, prevent, repel, mitigate or interrupt pest development, and it should be used as the last resource.

All pesticides used in United States must be registered through the EPA and the site (crop) of application must be listed on the pesticide label. There are few pesticides labeled for hemp, because federal regulation did not consider hemp as crop until recently. Up until 2021, the EPA has approved adding hemp to the labeled use sites of 59 pesticide products. Fifty-eight of the products are biopesticides and one is a conventional pesticide. Insecticides are pesticide products that are used to manage insects. The following table contains a list of active ingredients of insecticides labeled for hemp, commercial names and labeled pest: 

For information about hemp planting and production see the following link https://agriculture.wv.gov/wp-content/uploads/2020/10/Hemp-Fact-Sheet-5-19.pdf

References

Cranshaw W and Schreiner M (2018) Hemp Insect Factsheets. Colorado State University. https://agsci.colostate.edu/hempinsects/hemp-insects-text/

Osborne L S, McKenzie C, Popenoe J and Schoeller E. UF/IFAS Industrial Hemp Pilot project. University of Florida https://mrec.ifas.ufl.edu/hemp-insects-and-mites/

Environmental Protection Agency (EPA). Pesticide products registered for use on Hemp. https://www.epa.gov/pesticide-registration/pesticide-products-registered-use-hemp#biopesticide

Author: Carlos Quesada, WVU Extension Specialist – Entomology

Last Reviewed: November 2022

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