Evaluating herbicide tolerance of industrial hemp (Cannabis sativa L.)

Abstract

Industrial hemp (Cannabis sativa L.) has a wide array of end uses which, when coupled with regulatory reductions in the United States, has spurred renewed interest in its production. Best management practices, including weed control, need to be evaluated. Since little is known about herbicide tolerance of hemp, studies were conducted to identify suitable options for grain or dual‐purpose (fiber and grain) production. Greenhouse experiments with pre‐emergence and postemergence herbicides were conducted to identify herbicide choices for subsequent field trials. In field studies, S‐metolachlor was the safest pre‐emergence herbicide, resulting in 0 and ≤ 15% injury in 2017 and 2018, respectively, and a hemp stand count that was 97% of the nontreated check (pooled across years). All other pre‐emergence herbicides tested in the field resulted in ≥ 25% visible injury in at least one of the years and ≥ 24% stand reduction relative to the nontreated check (pooled across years). However, no grain yield differences were observed due to pre‐emergence herbicides relative to the nontreated check. Postemergence herbicides sethoxydim, quizalofop, bromoxynil, and clopyralid caused < 20% injury across rating timings and years and had similar grain yield as the nontreated check (588 kg ha−1). Our results indicate that S‐metolachlor applied pre‐emergence or sethoxydim, quizalofop, bromoxynil, and clopyralid applied postemergence are suitable for hemp production, but some of these treatments caused transient visible injury. Future research should be conducted to corroborate results across cultivars, soil types (for pre‐emergence herbicides), and environments.

Dose–response screening of industrial hemp to herbicides commonly used in corn and soybean

“…Amaducci et al (2015) advised against planting hemp in years following maize treated with atrazine. Metribuzin was found to reduce stand and plant height and to cause >70% biomass reduction in greenhouse applications (Flessner et al 2020). Fomesafen has been found to cause significant biomass reduction and highly variable injury (Flessner et al 2020;Maxwell 2016).…”

“…Metribuzin was found to reduce stand and plant height and to cause >70% biomass reduction in greenhouse applications (Flessner et al 2020). Fomesafen has been found to cause significant biomass reduction and highly variable injury (Flessner et al 2020;Maxwell 2016). Flessner et al (2020) found that encapsulated acetochlor did not reduce stand or height in greenhouse trials, but they did not test nonencapsulated acetochlor.…”

“…Fomesafen has been found to cause significant biomass reduction and highly variable injury (Flessner et al 2020;Maxwell 2016). Flessner et al (2020) found that encapsulated acetochlor did not reduce stand or height in greenhouse trials, but they did not test nonencapsulated acetochlor. Acetochlor is also recommended at varying rates for weed control in hemp in China (Amaducci et al 2015), but the recommended formulation is unknown.…”

“…The use of acetochlor (site of action [SOA] Group 15), metolachlor (SOA 15), and pendimethalin (SOA 3) in hemp is registered in China (Amaducci et al 2015), while ethalfluralin (SOA 3) and quizalofop-p-ethyl (SOA 1) are registered for hemp in Canada. Few preliminary studies outline hemp's tolerance to herbicides in the United States (Flessner et al 2020;Johnson and Willenborg 2018;Maxwell 2016;Sosnoskie and Maloney 2021). Although this research provides some insight to hemp's relative sensitivity to a wide range of herbicides, all previous trials were completed at one or two different rates for each active ingredient.…”

Studying the Effects of Waterhemp Competition on Yield and Phytochemical Content of High-cannabidiol Hemp in Plasticulture

“…However, weeds can still emerge through holes in plastic mulch and compete with the crop. U.S. producers typically rely on herbicides to control weeds, but there are currently no herbicides labeled for use in hemp in the United States (Flessner et al, 2020). Lack of control options makes understanding the effects of weeds on hemp yield and chemical composition a research priority (Ellison, 2021).…”