Mechanical and chemical control of cogongrass (Imperata cylindrica)

Field studies were initiated in 1985 and 1986 to evaluate the effects of dalapon, glyphosate, imazapyr, and sulfometuron applications to established cogongrass alone or in combination with either mowing or discing. Mowing and discing treatments were performed 4 mo before and 8 months after the herbicide treatments in the 1985 experiments and 2 months before and 7 months after the herbicide treatment in the 1986 experiments. When applied alone, glyphosate at 3.4 kg ai/ha and imazapyr at 0.8 kg ai/ha caused the greatest reduction in shoot and rhizome biomass about 2 yr after application, However, the rhizome infestation was reduced only 43% by glyphosate and 51% by imazapyr, as compared to the nontreated control. With no herbicide, two mowings or discings were generally more effective than a single mowing or discing treatment. The reduction in shoot and rhizome biomass for two mowings without herbicide was 65 and 38% and for two discings, 73 and 66%, respectively. Acceptable (> 80%) levels of cogongrass control, based on reductions in rhizome biomass occurred only when applications of dalapon, glyphosate, or imazapyr were made in combination with two discings despite the fact that mowing before and after treatment reduced shoot biomass by at least 89%.