Doctor of Philosophy (PhD)


Plant, Environmental Management and Soil Sciences

Document Type



Knotgrass (Paspalum distichum L.) and torpedograss (Panicum repens L.) are perennial grasses that are extremely difficult to remove in established turfgrass. Studies were conducted to determine the potential for controlling these troublesome perennial weeds. Pot studies were conducted for two years to evaluate several herbicides with multiple modes of action for knotgrass control. In graminicides studies, 8 weeks after initial application (WAI) single or split applications of fluazifop or quizalofop provided excellent control (88 to 95%). In contrast, single or split applications of fenoxaprop at 0.21 kg ha-1 and single applications of diclofop at 0.84 kg ha-1 were no better than the untreated check. Single applications of sethoxydim at 0.62 kg ha-1 were similar (85%) to sequential applications at 0.31 kg ha-1 (90%). MSMA, the industry standard, provided less than 40% control knotgrass control. In nonselective studies, glyphosate, glufosinate, and sulfosate were evaluated at equivalent rates (1.12, 2.24, or 4.48 kg ha-1). At 7 WAT, knotgrass control was at 99% for glufosinate, regardless of rate applied. All rates glyphosate and glufosinate or sulfosate applied at 2.24 and 4.48 kg ha-1 were similar and provided at least 95% knotgrass control. However, sulfosate applied at 1.12 kg ha-1 only controlled knotgrass 79%. In studies evaluating quinclorac, control was greater with the herbicide applied at the highest rate (2.24 kg ha-1). Knotgrass was not satisfactorily controlled, however, as control never exceeded 34%. Field and greenhouses studies were conducted to evaluate clethodim for torpedograss control in centipedegrass. Single or sequential applications of clethodim at 0.60 kg ha-1 and sequential applications at 0.30 kg ha-1 were more effective than sethoxydim applications. Torpedograss control with clethodim however, was not acceptable and did not exceed 79% throughout the study. Torpedograss control with sethoxydim was no greater than 55%. Although still commercially acceptable (< 30% injury), clethodim caused some moderate centipedegrass injury. In greenhouse studies, several spray adjuvants were evaluated to increase the efficacy of clethodim. Results indicated that herbicide rate is more critical than the adjuvant. Regardless of adjuvant, clethodim at 0.60 kg ha-1 controlled torpedograss better than the 0.30 kg ha-1 rate (62 vs 44%).



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

James N. McCrimmon