Weed Control

There are no herbicides registered for use on industrial hemp in Manitoba. A uniform stand that emerges ahead of weeds is very competitive. In conventional or organic production this competitive ability should be used to advantage. Field choice, pre-seeding tillage or burn off, soil temperature, shallow seeding, and packing after seeding all help to ensure that the hemp stand will emerge quickly and uniformly to gain advantage over the weeds.

Wild buckwheat and volunteer barley are seeds that are difficult to clean out of hemp grain. Avoid growing hemp in fields where these weed problems might exist. Volunteer barley or other cereals also present a marketing issue. Hemp is promoted in many markets as being gluten free so is attractive to people that have allergies. Cereals in the hemp grain would be a problem.

Herbicide use is a marketing issue as many of the contractors/processors specify in their contracts the herbicide use in the crop is not acceptable. Unregistered herbicide application resulting in potential residues could cause irreparable damage to the industry and markets.

Volunteer hemp control

Hemp regulations require that all volunteer plants be eliminated in following fields and years. Several herbicides like phenoxy types (although none are registered) have activity on hemp, Glyphosate and paraquat products would be suitable for pre-seeding applications.

Crop rotation planning after hemp is important to reduce the volunteer threat. Ensure there is herbicide efficacy on hemp in the crop that is planted following the hemp crop. It has been found that crops like Fababeans and liberty tolerant Canola’s are not a good crop to follow behind hemp. Liberty is a good herbicide and will kill small hemp plants. If hemp plants are larger or receive a low rate, they will often re grow after an application causing a volunteer weed problem that has to be controlled.