Recent legalization of industrial hemp in the US has led to increased interest among stakeholders to produce hemp for grain and fiber. However, due to the lack of herbicides registered for use in hemp, producers are left with limited weed management strategies. Moreover, much of the agricultural land that could be used to cultivate industrial hemp may be prone to carryover of previously applied residual herbicides or physical drift from herbicides sprayed nearby. Industrial hemp sensitivity to herbicides is not well documented. Dose response studies were conducted under controlled conditions in Madison, WI screening two industrial hemp grain cultivars for tolerance to 44 preemergence and postemergence herbicides commonly used in corn and soybean. Treatments consisted of herbicides applied at 0×, 0.125×, 0.25×, 0.50×, 0.75×, 1×, 2× and 4× the recommended maximum labeled rate based on soil type. Preemergence applications were delivered immediately after planting while postemergence applications took place when hemp plants reached 5-10 cm in height. Nontreated plants served as the control and were used to estimate percent biomass reduction; dose response curves were generated. Biomass reduction was >50% for rates under the suggested label rate for 23 preemergence- and 21 postemergence herbicides tested. All herbicides tested resulted in >25% biomass reduction at the 0.125× rate except for clopyralid applied preemergence and postemergence and saflufenacil applied preemergence. This is concerning, as the label rates are determined for effective weed control and the mitigation of herbicide resistance. Overall, these results indicate that industrial hemp is very sensitive to most herbicides tested. Growers should consider herbicide use history and surrounding crops when determining industrial hemp field selection to prevent significant plant injury due to herbicide carryover and drift. Further research into alternative methods of weed control will be vital to establishing hemp as a dominant crop once again.

After decades of heavy regulation, growers across the United States were able to begin growing industrial hemp (Cannabis sativa L.) again in 2014. The 2014 and 2018 Farm Bills made it legal for research and production to resume and removed hemp from the list of controlled substances. Because of the long prohibition of hemp production, many questions surrounding best management practices still exist. In 2019 and 2020, studies were conducted in Arlington and Chippewa Falls, Wisconsin to evaluate the effects of cultivar, seeding rate, and nitrogen rate on hemp yield. Two cultivars (X-59 and CRS-1), seeded at three seeding rates (22, 34, and 45 kg ha −1 ) and three nitrogen rates (0, 67, and 134 kg ha −1 ), were evaluated. At Arlington, nitrogen did not impact fiber yield; however, an interaction among cultivar, seeding rate, and nitrogen rate effected grain yield. At Chippewa Falls, fiber yield increased by 20% when nitrogen rate increased from 0 to 67 or 134 kg N. Similarly, grain yield increased by 52% when the nitrogen rate increased from 0 to 67 or 134 kg ha N. The effect of seeding rate alone was highly variable with no consistent pattern on response variables measured. Therefore, the overall effect of nitrogen rate was more consistent than the effect of seeding rate on response variables measured. Ultimately, management recommendations will be dependent on local conditions; however, hemp does respond to the addition of nitrogen fertilizer. INTRODUCTIONWisconsin was the leading producer of industrial hemp (Cannabis sativa L., further referred to as 'hemp') from 1920