Effect of early and late post emergence herbicides on weed suppression, crop injury, and biomass yield of industrial hemp in semiarid conditions

Abstract Industrial hemp is receiving attention for its numerous benefits, particularly in the fiber industry. Weed competition is a primary concern for hemp cultivation, causing reduced yields and inferior‐quality fiber. However, little is known about herbicide application in hemp since a limited range of herbicides are available for hemp production. During 2023, this study evaluated the effect of different post‐emergence herbicides applied at early and late growth stages to optimize weed suppression and minimize crop injury in hemp under semiarid conditions. A randomized complete block design was used with six herbicide treatments, including early post (2 weeks after planting [WAP]) and late post (5 WAP) emergence applications of S ‐metolachlor, clopyralid, and ethalfluralin. Hemp plant stand showed no significant difference among treatments. Early post herbicide application reduced 86% of weed biomass compared to untreated control at 7 WAP. By 10 WAP, weed biomass became comparable across treatments. At harvest, untreated control recorded comparatively higher weed biomass than early post treatments and late post ethalfluralin. Plant height remained nonsignificant among treatments until 10 WAP. At harvest, control showed no variation with late post treatments but recorded an average of 63% lower plant height than early post applications. Hemp biomass was insignificantly affected by treatments at 10 WAP. However, on average, early post S ‐metolachlor and ethalfluralin applications demonstrated potential as effective herbicides, yielding four‐folds greater hemp biomass than untreated control at harvest. In conclusion, early post S ‐metolachlor and ethalfluralin are promising tools for weed control, enhancing crop competitiveness and yield in hemp cultivation.