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Hemp plant ready to be harvested. Image courtesy of NC State University. Credit: NC State University College of Agriculture and Life Sciences.

IR-4 Petition Yields First Conventional Pesticide Tolerance for Hemp

Nifa Authors
Lori Tyler Gula, Senior Public Affairs Specialist

Hemp growers seeking more pest management tools now have a conventional pesticide tolerance for hemp seed as a result of work by the Minor Crop Management Program Interregional Research Project #4, or the IR-4 Project, which is funded by USDA’s National Institute of Food and Agriculture (NIFA).  

The following story originally appeared on the IR-4 website and is repurposed here with permission.

Approved for use by the Environmental Protection Agency (EPA), ethalfluralin, a conventional herbicide already used on crops like soybeans, peanuts and potatoes, will help hemp growers manage annual broadleaf and grassy weeds that compete with young plants. While there already were biopesticides registered for use on hemp, growers wanted more tools in their toolbox to grow hemp successfully, especially at a larger scale. 

“With the establishment of a tolerance for ethalfluralin, growers will have access to a useful tool to help effect control of annual broadleaf and grassy weeds in their hemp fields,” said Dr. Michelle Samuel-Foo, a national program leader in NIFA’s Institute of Food Production and Sustainability—Plant Protection Division. “IR-4 played a critical role in this process as they were able to submit a Chemistry Science Advisory Council proposal to the EPA, which allowed for extrapolation of existing data to make the determination that no residues would be left in hemp plants after application of the chemical according to its label.” 

After the 2018 Farm Bill authorized the production of hemp and removed hemp and hemp seeds from the controlled substance list, interest in growing the crop skyrocketed. With this hype around hemp came the demand for approved pest management tools. IR-4 is working with partner agencies and researchers to generate data and facilitate the registration of products to meet hemp growers’ needs, and this ethalfluralin tolerance marks the first success.  

“Having another tool in our very small IPM toolbox for hemp is critical,” said Dr. David Suchoff, alternative crops Extension specialist at North Carolina State University. “Weeds, especially in the Southeast, pose our biggest challenge. Our small-plot trials utilize ethalfluralin, and we have seen excellent weed control.” 

IR-4 Fills an Essential Niche 

Determining how to approach the regulation of pest management products for hemp posed a significant challenge to EPA. Since hemp is a relatively new crop (with scores of possible uses), the EPA was uncertain about what residue studies would look like; what parts of the plant to study; and what kinds of risks would need to be assessed. It was, and still is, new territory. 

According to Nancy Fitz, minor use team leader at EPA’s Office of Pesticide Programs, EPA needed IR-4’s expertise to navigate this uncertain landscape; IR-4 filled an essential niche.  

IR-4 gathered data that could be reasonably extrapolated to help EPA assess potential risks associated with using ethalfluralin on hemp seed. Some of the data came from studies done in Canada. IR-4’s longstanding collaborative relationship with the Canadian Pest Management Centre helped expedite the data gathering and petition process.  

In October 2020, IR-4 submitted its petition to EPA requesting tolerances be established for residues of ethalfluralin on hemp seed and several other crops. Based on IR-4’s petition, EPA issued a final rule on April 10 establishing these tolerances.  

Early morning sun illuminates new hemp plants growing in Broadway Hemp’s Harnett County greenhouse. Credit: NC State University College of Agriculture and Life Sciences.
Early morning sun illuminates new hemp plants growing in Broadway Hemp’s Harnett County greenhouse. Credit: NC State University College of Agriculture and Life Sciences. 

IR-4’s Role in Hemp’s Evolving Pest Management Needs 

Compared to other crops, hemp is in its infancy in terms of data, experience and regulatory preparedness to grow it at scale. IR-4 is hard at work—along with Cooperative Extension and Land-grant researchers across the country—exploring pest management strategies to support hemp growers in this emerging industry.  

Growing hemp for different uses (flower, fiber, seed or feed) requires harvesting at different stages in the life cycle. This means farmers may encounter different pest challenges depending on their intended use or market. Weed management is the key issue in the seedling stage; once plants are established, their lush canopy can effectively shade out weeds. In the flowering stage, disease and insect pressure is more likely. 

“Currently, IR-4 is looking at a range of products that will address foliar and root pathogens, mites and grass weeds,” said Cole Smith, an IR-4 field research director at NC State University. “As the market shifts towards fiber, weeds are becoming more of a challenge for hemp growers.” 

North Carolina-based hemp grower and agricultural consultant Bert James highlighted a disconnect between public perception of conventional pest management and what growers need to make hemp work for them.  

“There is a strong desire to keep hemp this fresh and clean crop, with limited need for pesticides, fungicides and herbicides. That doesn’t align with the farmers—at least not the range of farmers we have in our area,” James said. “So it’s a bit of a disconnect—there’s a happy medium between these two groups, and I like to be a reality check. With one residual application, we could grow hemp any time of the year; as it stands, we can’t plant anytime beyond mid-May because of the pigweed issues.” 

“Crops like hemp that are slow and vulnerable like cotton in the first few weeks benefit greatly from a residual herbicide that prevents established weeds and grasses that are well acclimated to different geographies from outpacing the new crop being introduced,” he said. “Future practices like improved soil health and the right cover crop combination to be established for future crops are also valuable.  These natural processes take time, sometimes years to become truly effective.”   

Farm Bill Priority Areas
Plant health, production, and products
U.S. States and Territories
North Carolina

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