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. Therefore, a field study was conducted in 2023 to investigate the effect of different herbicides and application timings on weed suppression, crop injury, growth, and biomass yield of hemp. A randomized complete block design was conducted 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, with an untreated control to make comparisons. Plant stand showed no significant difference among treatments. Early POST herbicides application significantly reduced the 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 non-significant among treatments until 10 WAP. At harvest, control showed no variation with late POST treatments but recorded an average 63% lower plant height than early POST applications. Treatments showed no significance for hemp biomass at 10 WAP. However, early POST S-metolachlor and ethalfluralin herbicides exhibited lower weed biomass and greater plant height, resulting in greater hemp biomass accumulation compared to untreated control at harvest. In conclusion, early POST S-metolachlor and ethalfluralin could be used as POSTemergence herbicides for hemp cultivation.
Field production hemp trials were conducted in 2020 and 2021 in Baton Rouge, Louisiana without success. In both seasons, the hemp was planted in spring and harvested in early summer. Over 50% of the plants dies from disease and or initial root rot because of excessive rain and wet soils. Faculty at the LSU AgCenter were successful in growing hemp in 2021 in greenhouse settings but realize not all growers can afford such structures. Therefore, field trails were established in the fall 2023 (October) and early spring (January and February 2024) planting dates. Day length neutral hemp was planted. The off-season trials were planted in attempt to field produce hemp during cooler and drier weather to prevent plant loss from disease. Unfortunately, the field plantings in October 2023, January and February 2024 yielded small plants with little harvestable flowers. At this time, we do not recommend field planting hemp in south Louisiana.
Heather Kirk-Ballard is an Assistant Professor and state extension specialist of Consumer Horticulture for the LSU AgCenter. She is the host of the Get It Growing ™ extension program focusing on home gardening that is disseminated weekly through video to news stations and in print... Read More →
