Response of industrial hemp ( Cannabis sativa L.) to preemergence herbicides and weed control under different nitrogen fertilization

With the recent development of commercial prospects, there is increased interest in commercializing industrial hemp (Cannabis sativa L.) in the United States. A two-year study was conducted to evaluate the response of industrial hemp to selected preemergence herbicides and weed control under different nitrogen (N) fertilizations. While S-metolachlor and pendimethalin caused no significant injury in 2023, at 2 weeks after treatment (WAT), hemp injury was 37% and 21% in 2022. S-metolachlor and pendimethalin reduced hemp height by ≥15% compared to the weed-free control at 2 WAT. Pendimethalin reduced crop stand by ≥20% compared to the weed-free control at 4 WAT. Nitrogen at 168 kg ha−1 increased hemp height by more than 30% compared to 84 and 0 kg ha−1, and produced dry stalk yield of 5,500 kg ha−1 and 4,050 kg ha−1 in 2022 and 2023, respectively. Compared to the non-treated weedy control, pendimethalin, and S-metolachlor provided excellent control of 80–90% of all the weeds observed. Hemp seed yield was 50% to 60%, and stalk yield increased by 20%-50% in the herbicide-treated plots compared to the nontreated weedy control. Enhancing the performance of industrial hemp through adequate N levels and pre-emergence herbicides could boost hemp seed and stalk yields.