Tumble windmill grass (Chloris verticillata Nutt.) control with POST herbicides

Tumble windmill grass (Chloris verticillata Nutt.) is a problematic perennial grass weed in the semiarid Central Great Plains (CGP). Greenhouse and fallow field experiments were conducted during 2021 and 2022 at Kansas State University Agricultural Research Center near Hays, KS, to determine the effectiveness of various POST herbicides for tumble windmill grass control. All selected POST herbicides were applied at field-recommended rates at the seedling growth stage (3-to 4-inches tall) of tumble windmill grass in greenhouse study. Tumble windmill grass was at the heading growth stage (10-to-12-inches tall) in fallow fields when POST herbicides were tested. Results from greenhouse study indicated that quizalofop-P-ethyl (QPE) and clethodim provided ≥ 95% control and shoot biomass reduction of tumble windmill grass at 28 days after treatment. Glyphosate provided 89% control and 93% shoot biomass reduction of tumble windmill grass. Imazamox and nicosulfuron had the least control (41 to 51%) and shoot biomass reduction (43 to 66%) of tumble windmill grass in greenhouse study. In contrast, all tested POST herbicides were comparatively less effective on tumble windmill grass (≤68% control and ≤ 50% shoot biomass reduction) except glyphosate (85% control and 54% shoot biomass reduction) in field study. These results conclude that clethodim, QPE, and glyphosate applied at early growth stages can provide effective control of tumble windmill grass in the CGP region.Core Ideas Efficacy of POST herbicides was evaluated for tumble windmill grass control in greenhouse and field studies. Clethodim and quizalofop-p-ethyl applied at the seedling stage provided ≥95% control and shoot dry weight reduction of tumble windmill grass in greenhouse. Majority of tested POST herbicides applied at heading stage provided unacceptable control (≤68%) of tumble windmill grass, except glyphosate (85%) in field study.