MEFLUIDIDE APPLICATIONS FOR ANNUAL BLUEGRASS SEEDHEAD SUPPRESSION BASED ON DEGREE-DAY ACCUMULATION

Mefluidide [N-(2,4-dimethyl-5-{[(trifluoromethyl)sulfonyl]amino}phenyl)acetamide] is an effective growth regulator for annual bluegrass [Poa annua var. reptans (Hauskins) Timm.] seedhead suppression. The effectiveness of mefluidide is dependent on the rate and timing of application. The objective of this field study was to determine the lowest effective rate and the proper time for mefluidide application based on growing degree-days (GDD). Soil types were a fine, mixed, mesic Aeric Ochraqualf and fine-loamy, mixed, mesic Typic Glossoboric Hapludalfs for Columbus, OH, and East Lansing, MI, respectively. The rates evaluated were 0.140, 0.070, and 0.035 kg ha-1 of mefluidide. The applications were at 15, 25, 30, and 45 GDD. Degree-days were accumulated using a sine curve as an approximation of the diurnal temperature curve. The base temperature used was 13.degree. C. Mefluidide applied between 15 and 30 GDD at 0.140 kg ha-1 gave excellent seedhead suppression. Mefluidide applied between 15 and 30 GDD at 0.070 kg ha-1 gave moderate seedhead suppression. Applications of mefluidide at 45 GDD or at the 0.035 kg ha-1 rate were unacceptable.