Bugs, biology, biodiversity: Industrial Hemp Production (Part II) on Integrated Pest Management and Implications for Wildlife

By Susan P. Rupp, PhD, Lee Enterprises Consulting

Special to The Digest

Because of the challenges of registering it as an agricultural crop, federal agencies have not yet provided clear direction on the use of agrochemicals (i.e., herbicides, pesticides, and fungicides) on hemp, and regulatory decisions have subsequently devolved to the states.  However, the majority of states that have allowed hemp production have not addressed the issue, taking the position that only the federal government can regulate pesticide use on the crop (Cranshaw et al. 2019).  As a result, growers must follow good cultural practices to reduce the impact of pests and weeds.  Practices such as “integrated pest management” (IPM), though challenging to implement, can provide significant benefits to both crop production and environmental sustainability.  This article is meant to introduce the readers to the basics of IPM as well as implications for wildlife of hemp production and management.

What is “Integrated Pest Management”?

Integrated pest management, or IPM, is a sustainable, ecological approach to managing pests that focuses on a combination of cultural techniques, mechanical methods, and biological controls rather than simply finding chemical solutions to pest issues.  Cultural techniques alter the farmscape, making it less favorable for pests and disease organisms; mechanical methods utilize traps, barriers, and other creative techniques; and biological controls employ beneficial organisms to subdue pests and pathogens (McPartland et al. 2000).  Employing the right combination of cultural, mechanical, and biological controls in the right order for a given landscape and environment in order to provide the most effective management is both an art and a science. Ideally, use of agrochemicals should be a last resort because of the risks they can pose to humans, animals, and the environment.

It should be noted at this point that organic farming differs from IPM in one fundamental aspect; organic farmers eschew the use of synthetic pesticides whereas IPM uses any legal pesticide that works. However, unlike conventional farming practices where agrochemicals are often sprayed based on calendar date, farmers who employ an IPM framework often spray on a schedule determined by three aspects: 1) pest monitoring, 2) climate monitoring, and 3) the presence of beneficial organisms (McPartland et al. 2000). Farmers utilizing IPM must closely monitor crop conditions, biological control organisms, the weather, and all pests in an area though knowledge of a complex web of ecological relationships, such as parasitism, mutualism, and competition (ibid.).  In essence, farmers employing an effective IPM regiment are working with nature instead of against it.

Though an in-depth review of various mechanical, cultural, and biological controls for hemp production is not feasible here, several examples can be provided for each.  Common cultural practices for limiting pest and disease issues include proper sanitation such as destroying crop residues after harvest that might harbor pests or disease, cleaning and/or sterilizing equipment and clothing after use, maintaining a clean workspace, ensuring adequate airflow among plants to prevent accumulation of moisture that might promote fungal growth, and proper seeding/planting dates.  Mechanical controls may be as simple as picking off pests from plants when observed, proper tillage methods that reduce soil compaction without compromising soil integrity, or pruning away fungus-infected branches.  Biological control may include simply enticing some naturally occurring predators (e.g., ladybeetles, lacewings, native songbirds) to stay in crops or actually introducing biological controls such as parasitic wasps that lay eggs in larvae of pest species subsequently killing off the pest (and, eventually, the parasitic species once the food source has been depleted). For a more thorough review of IPM techniques, readers are referred to McPartland et al. (2000) as well as their local Extension offices.

Hemp and Wildlife

Though agronomic crop farmers often focus on insect “pests” and their management, there is also a need to recognize the beneficial role some wildlife have in crop production.  For example, hemp cultivars grown to maximize oilseed yield will be grown from seed and require pollination. In fact, hemp grown for seed, fiber, or dual-purpose (seed and fiber) are heavy pollen producers in the summer and serve as an off-season food source (no nectar is produced) for bees and other pollinators (Cranshaw et al. 2019, Mitchell and Uchanski 2020). O’Brien and Arathi (2019) reported 20 different genera of bees on flowering hemp demonstrating that hemp in the agroecosystem supports pollinators. This is critical because pollination is an often under-recognized essential ecosystem function of significant economic importance worldwide.  Pollinators contribute >$24 billion/yr to the U.S. economy, honey bees contribute ~$15 billion/yr, and native pollinators ~$9 billion/yr.  Given that pollination is required for >75% of food crops worldwide, hemp as a supplemental crop for pollinators could have significant economic benefits.

Despite the potential benefits to some pollinator species, however, hemp crops can be prone to a variety of insect pests that vary depending on where they are located within the U.S.  There are reviews of pest arthropods of hemp (e.g., McPartland et al. 2000), with roughly 300 species worldwide known to colonize the crop.  Among key pest species, corn earworm, Helicoverpa zea), has demonstrated the greatest potential for crop injury, being particularly damaging to flower buds, whereas hemp russet mite, Aculops cannibicola, and cannabis aphid, Phorodon cannabis Passerini, are the two species observed to be most damaging among those that suck plant fluids (Cranshaw et al. 2019). Though numerous species of caterpillars, grasshoppers, and beetles chew hemp foliage, the severity appears to be minimal (Cranshaw et al. 2019). Similarly, numerous seed feeding hemipterans, most notably stink bugs and Lygus bugs, are regularly found in the crop but further research is needed (ibid.)

In addition to existing regulatory barriers that currently prevent the use of several insecticides, challenges in pest management arise because many insects, notably seed feeding hemipterans and the Eurasian hemp borer, develop highest and most damaging populations during periods when the crop is in flower and being used by bees (Cranshaw et al. 2019). This will be a confounding factor to consider in the registration and use of pesticides on hemp during periods when pollen production makes plants attractive to bees. Because pollinators are currently suffering major declines due to increased use of pesticides (which cause direct mortality to insects) and herbicides (which reduce available habitat), an IPM approach is ideal.

Though little research has been done on interactions of other wildlife with industrial hemp crops in recent years, there is some indication in the literature that birds and mammals may have some interest in the crop. Game birds including quail, pheasants, and doves along with other non-game songbirds may consume hemp seed.  Furthermore, insects found in hemp crops may serve as a food source for birds and small mammals as well.  Rodents, rabbits, and deer may use hemp and it has been noted that high levels of THC may harm ruminants (cows, sheep, deer) because of its antibacterial activity (McPartland et al. 2000). Any use of pesticides or herbicides can also harm wildlife by directly reducing their food sources or changing the habitat on which they rely. One must also recognize of the risk associated with bioaccumulation of agrochemicals in the environment, which has the potential to impact other fish and wildlife populations.

It is good practice for producers to contact their local Extension offices to seek information specific to their locales and to develop an IPM system to improve yields while reducing risks to beneficial ecosystem services.  Additional production information and technical assistance can also be acquired through natural resource agencies such as the Natural Resources Conservation Service (NRCS), who administer Farm Bill programs.

Next Up: “Hemp Biomass Management: Technology Development and Mitigating Scale-up Risks” by David F. Peterson.

About the author: Dr. Susan Rupp is V.P. of the Land & Natural Resource Section at Lee Enterprises Consulting, the world’s premier bioeconomy consulting group, with more than 150 consultants and experts worldwide. The opinions expressed herein are those of the author and do not necessarily express the views of LEC.

References

Cranshaw, W., M. Schreiner, K. Britt, T. P. Kuhar, J. McPartland, and J. Grant.  2019.  Developing insect pest management systems for hemp in the United States.  Journal of Integrated Pest Management 10(1): 26; 1–10

McPartland, J. M., R. c. Clarke, and D. P. Watson.  2000.  Hemp diseases and pests: Management and biological control.  CABI Publishing, CAB International, London, United, Kingdom.  251 pp.

Mitchell, B. A., and M. E. Uchanski.  2020.  Industrial hemp: reemergence of an alternative crop in the U.S.  Fact Sheet 0.311.  Colorado State University Extension.  Fort Collins, Colorado.

O’Brien, C. and H. S. Arathi.  2019.  Bee diversity and abundance on flowers of industrial hemp (Cannabis sativa L.).  Biomass and Bioenergy 122:331-335.