Sensitivity of TamArkTM Grain Sorghum and Monocot Weed Species to ACCase- and ALS-inhibiting Herbicides

Postemergence selective monocot control in grain sorghum is an issue due to the limited number of herbicides available. The herbicides currently labeled in grain sorghum have strict use restrictions, low efficacy on johnsongrass, or weed resistance issues. To introduce a new effective herbicide mode of action for monocot control, multiple companies and universities have been developing herbicide-resistant grain sorghum that would allow producers to utilize either acetolactate synthase (ALS) or acetyl coenzyme A carboxylase (ACCase) inhibitors for postemergence monocot control. An experiment was conducted in Fayetteville, AR, in 2020 and 2021 to determine the effectiveness of two ALS-inhibiting herbicides and nine ACCase-inhibiting herbicides on TamArkTM grain sorghum, conventional grain sorghum, and problematic monocot weed species. Grain sorghum and monocot weeds (johnsongrass, broadleaf signalgrass, barnyardgrass, and Texas panicum) were sprayed when TamArkTM grain sorghum reached the 2- to 3-leaf stage. TamArkTM grain sorghum was tolorant to all ACCase-inhibiting herbicides tested exhibiting ≤10% injury at all evaluation timings, except clethodim and sethoxydim, and had no resistance to the ALS-inhibiting herbicides evaluated. Additionally, all ACCase inhibitors except diclofop and pinoxaden controlled all monocots tested >91% by 28 days after application (DAA). Conversely, the two ALS inhibitors, imazamox and nicosulfuron had ≤81% control of broadleaf signalgrass 28 DAA but still controlled all other monocots >95%. TamArkTM grain sorghum 'has low sensitivity to multiple ACCase-inhibiting herbicides thus providing an effective POST option for monocot weed control and unwanted volunteer TamArkTM plants can be controlled with cledthodim, sethoxydim, nicosulfuron, or imazamox has low sensitivity to multiple ACCase-inhibiting herbicides. Imazamox and nicosulfuron, both ALS-inhibiting herbicides, while not useful on TamArkTM grain sorghum, are effective options for monocot control in IgrowthTM and InzenTM grain sorghum, respectively.