Hemp is not very competitive with weeds in the first 3-4 weeks of growth. Hemp for grain or CBD is planted at a lower density per acre compared to fiber hemp. The lower plant density can reduce or prevent canopy closure, allowing for more weed competition.
Weed control is one of the largest issues in hemp production. We have no synthetic herbicides registered for use in hemp, either as a pre-emerge or post- emerge application, in the United States. Herbicide screening is underway at universities across the county, including Purdue and Vincennes University.
Choosing field sites with low weed pressure to begin with, is the best preventative measure to reduce weed competition. Rotating after crops where you can use conventional weed management may be an option, just be aware that limited research has been done on herbicide rotation restrictions in hemp. Create a weed management plan before you plant your seeds!
Growers are using various methods for weed suppression and control including; pre-plant cultivation, in-row cultivation, and mowing. Weeding equipment common in organic systems is also an option. In CBD hemp, the laying of plastic is one method to suppress weeds within the row. Some growers are also using cover crops for weed suppression. The cover crops may be terminated before planting or left to live between the rows of hemp.