Controlling Volunteer Industrial Hemp in a Succeeding Corn Crop

There is a new crop on the block. In 2019, American farmers grew 511,442 licensed acres of industrial hemp, an increase of 78,176 acres over 2018. Hemp acreage expanded significantly across the United States after the 2018 Farm Bill lifted restrictions on its growth for commercial and academic research production. Currently, 46 states have laws allowing for hemp production and 34 states have instated laws for industrial hemp cultivation.1

The market for hemp is expanding because of the many end uses for hemp. Hemp is being used for food, nutritional purposes, clothing, a replacement for plastic, fuels, medical and pharmaceutical purposes, and much more.2  

With this nearly 500% expansion of hemp acres in the United States, many farmers will be rotating their hemp acres for the first time in 2020. Just like any other row crop, hemp acres should be rotated to prevent the buildup of disease inoculum in the soil and limit insect feeding pressure. Rotation helps keep volunteer hemp plants (the product of the inadvertent spread of hemp seed from the previous cropping season) from developing in the 2020 crop. Currently, there are no specific regulations in the United States dictating the control of volunteer hemp. However, our neighbors to the north have already imposed licensing regulations for the control of volunteer hemp plants in subsequent crops. According to the Canadian Hemp Trade Alliance, Health Canada licensing requires the elimination of volunteer hemp plants growing the next year.

What are some options for controlling volunteer hemp in a subsequent corn crop? The good news? When it comes to volunteer control, fields should start clean with either a spring cultivation or a burndown followed by an in-crop application of a broadleaf or nonselective herbicide such as glyphosate (Roundup® agricultural brand herbicides), dicamba, 2,4-D or glufosinate (Liberty® herbicide), which can give excellent control of volunteer hemp. Paraquat (Gramoxone® herbicide) is another option for burndown control of volunteers.3 As hemp plants become taller (greater than 2 inches), they become more difficult to kill with contact herbicides like glufosinate (Liberty herbicide).3 Contact herbicides may only burn the leaves that can allow the plant to recover from any viable node.3 Therefore, systemic herbicides are likely the most effective option for control. Please consult with your local seed dealer or Seedsman to help ensure your corn product contains the necessary herbicide-tolerant traits and does not have a specific caution or sensitivity to plant growth regulators.

Sources:

1Hemp acreage jumps 500% in 2019, a sign of legalization’s impact. 2019. Hemp Industry Daily. https://hempindustrydaily.com/.

2Vaught, J. 2019. Growing hemp. AgFunder News. https://agfundernews.com/.

3Hemp Production eGuide. 2019. Control of volunteer hemp. Canadian Hemp Trade Alliance. http://www.hemptrade.ca/.

Web sites verified 12/20/19

Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.

ALWAYS READ AND FOLLOW GRAIN MARKETING AND ALL OTHER STEWARDSHIP PRACTICES AND PESTICIDE LABEL DIRECTIONS. Tank mixtures: The applicable labeling for each product must be in the possession of the user at the time of application. Follow applicable use instructions, including application rates, precautions and restrictions of each product used in the tank mixture. Not all tank mix product formulations have been tested for compatibility or performance other than specifically listed by brand name. Always predetermine the compatibility of tank mixtures by mixing small proportional quantities in advance. Channel® and the Arrow Design® and Seedsmanship At Work® are registered trademarks of Channel Bio, LLC. Roundup® is a registered trademark of Bayer Group. Gramoxone® is a registered trademark of a Syngenta group company. Liberty® is a trademark of BASF Corporation. Some of the product(s) discussed herein are restricted use pesticide(s) and may not be registered in all states. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. Check with your local dealer or product representative for the product registration status in your state. All other trademarks are the property of their respective owners. ©2020 Bayer Group. All rights reserved.

Whitney Monin

Channel Technical Agronomist

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