Evaluation of Clethodim, Glufosinate, and Glyphosate Alone and in Tank-Mix with Residual Herbicides for Control of Johnsongrass (Sorghum halepense) Shoots and Rhizomes

Johnsongrass is one of the most difficult weeds to control due to its ability to regenerate from underground rhizomes. Johnsongrass has been a problematic weed for years in row crops in Mississippi. It can severely reduce yields in corn, cotton, soybean, and other row cropping systems. Two separate field studies were conducted in 2023 at the Delta Research and Extension Center in Stoneville, Mississippi to evaluate the effectiveness of clethodim, glufosinate, and glyphosate applied alone or tank-mixed with residual herbicides for johnsongrass rhizomes and seedlings control. No crops were included in this study, as it was carried out under non‑crop conditions. The experiment was conducted as a randomized complete block design with 12 herbicide treatments and three replications in a natural johnsongrass population (rhizomes and seedlings). Herbicide treatments included clethodim, glyphosate, and glufosinate applied alone or tank‑mixed with the residual herbicides brake, boundary, or acuron for control of johnsongrass rhizomes and seedlings. Johnsongrass shoot control from the application of clethodim alone was 83% four-weeks after application. Antagonism occurred when boundary or acuron were mixed with clethodim which reduced aboveground biomass control. Both glyphosate and glufosinate, whether applied alone or with residual herbicides, maintained excellent shoot control (>96%) with no evidence of antagonism. Four weeks after application, the entire test area was mowed down (after final johnsongrass evaluation) for possible johnsongrass regrowth. Johnsongrass regrowth was observed following all treatments except the glyphosate application. The residual herbicides brake, boundary, and acuron did not improve clethodim or glufosinate performance in preventing johnsongrass regrowth from rhizomes. Glyphosate alone or tank-mixed with residual herbicides were the only treatments that provided 100% of johnsongrass control with no-regrowth.