A uniform crop stand that emerges ahead of weeds is important. After the crop stand is established, hemp becomes a strong competitor to weeds. Wild buckwheat can be a major weed problem as the plant grows up the stem and produces seed at the same height as the hemp seed. Furthermore, wild buckwheat seed is difficult to separate from hemp seed. Perennial weed control should be done in the year prior to seeding hemp.
Several herbicides have activity on hemp, although none are registered for that use.
Glyphosate products and Gramoxone PDQ would be suitable for pre-seeding applications. The use of in-crop broadleaf weed herbicide with some residual activity may minimize volunteer problems. Cultivation can be used to control hemp in fallow situations, but several passes may be necessary. Extreme care must be taken to avoid contamination of grain of following crops with the seeds of volunteer hemp as this will lead to the rejection of shipments in some countries. No fungicides are registered for use in hemp.