Sorghum tolerance and weed control with amicarbazone and metribuzin applied preemergence

Abstract

Groundwater contamination has prompted the Environmental Protection Agency to consider restricting atrazine use, highlighting the need for alternative preemergence herbicides in grain sorghum ( Sorghum Moench). Research was conducted in 2023 and 2024 to evaluate grain sorghum tolerance and weed control from preemergence applications of amicarbazone (490, 735, and 980 g ai ha ⁻¹ ) and metribuzin (280, 420, and 560 g ai ha ⁻¹ ), applied alone and in combination with commonly used herbicides. Metribuzin applied alone caused ≤3% injury across evaluation timings, whereas amicarbazone at 980 g ha ⁻¹ caused 17% injury 5 weeks after treatment (WAT). Combining amicarbazone (980 g ai ha ⁻¹ ) with metribuzin (560 g ha ⁻¹ ) resulted in 38% injury, delayed panicle emergence by 3 days, and reduced grain yield by 43% points compared with the nontreated control. Weed control trials evaluated preemergence combinations of amicarbazone, metribuzin, atrazine, S ‐metolachlor, and mesotrione. On a silt loam soil, amicarbazone provided comparable Palmer amaranth control to atrazine 4 WAT in 2023 and greater weed control in 2024. Greater than 96% control of broadleaf signalgrass, common lambsquarters, spurred anoda, and ivyleaf morningglory 4 WAT was achieved with amicarbazone alone or with S ‐metolachlor + mesotrione preemergence. Amicarbazone + metribuzin resulted in similar weed control, but this treatment induced up to 40% injury to grain sorghum. Although effective weed control was achieved with amicarbazone + metribuzin treatments, injury and grain yield reductions warrant additional research to find a less injurious preemergence alternative to atrazine or a herbicide safener for amicarbazone + metribuzin in grain sorghum.