Abstract

Dollarweed canopy cover is reduced in lawns of St. Augustinegrass by reducing irrigation frequency, but without herbicides cultural management does not provide acceptable weed reduction. Field studies were performed to assess the interaction of irrigation interval and postemergence broadleaf herbicides to reduce dollarweed in St. Augustinegrass turf, and to determine optimum combinations of irrigation interval and herbicide. Under daily irrigation, among atrazine (2-chloro-4-(ethylamine)-6- -s-triazine) at 2.24 kg ai ha-1, Metsulfuron (Methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoate) at 0.021 kg AI ha-1, sulfosulfuron at 0.066 kg AI ha-1, and their combinations, the most extended reduction was obtained from atrazine mixed with either metsulfuron or sulfosulfuron, (N-[[(4,6-dimethoxy- 2-pyrimidinyl)amino]carbonyl]-2-(ehtylsulfonyl)imidazo{1,2-a]pyridine-3-sulfonamide) but dollarweed reduction was >85% only through 8 wk after initial treatment. Under delayed irrigation (2, 4, or 6-day irrigation interval) there were herbicide X irrigation interval interactions, and there was >85% reduction of dollarweed from some combinations of irrigation interval and herbicide. The most effective combinations were 6-d irrigation interval following sulfosulfuron application, and 4-d or 6-d irrigation interval following application of atrazine + sulfosulfuron.