Post-Emergence Control of Windmill Grass Using HPPD Herbicides.

Windmill grass (Chloris spp.) is a becoming a wide-spread weed on established turf in Missouri and surrounding states. Limited information is available regarding post-emergence control options for cool-season turf. This project aimed to utilize 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors for control of windmill grass under greenhouse conditions. Treatments, including mesotrione or topramezone, applied at label-suggested rates alone or in tank-mixing with triclopyr, were arranged in a randomized complete block design with 5 replications. Herbicide efficacy, evaluated weekly as percent injury and above-ground biomass collected at 4 weeks after treatment (WAT) were recorded. At 3 WAT, windmill grass receiving triclopyr in tank-mixing with mesotrione or topramezone reached 100% control. HPPD herbicides alone, however, showed 40~50% injury compared to control. Similar results were found in the above-ground biomass at 4 WAT. After 2 weeks’ regrowth, both HPPD herbicides in tank-mixing with triclopyr appeared to completely killed windmill grass. In comparison, various levels of regrowth were found in plants received HPPD herbicide alone. It was surprise to find that triclopyr alone resulted in >90% injury at 2 WAT. Although plants started to recover by 2 weeks after harvesting, triclopyr appeared to be promising in suppressing the growth of windmill grass. Collectively, our results suggested that HPPD herbicides in tank-mixing with triclopyr provide satisfactory windmill grass control.