Duration of yellow nutsedge (Cyperus esculentus) competitiveness after herbicide treatment

Experiments were initiated to determine the amount of time required for postemergence herbicides to render yellow nutsedge physiologically noncompetitive. The rate of net CO2assimilation (AN) was chosen as the response variable to describe competitiveness. Specifically, the time required after herbicide treatment forANto drop to 50% of that of the untreated control (AN50) was determined.AN50values for halosulfuron, imazapic, glyphosate, and MSMA were 1.6, 2.1, 3.2, and 3.3 d, respectively. AnAN50value was not calculated for bentazon becauseANrapidly decreased below 50% but recovered to > 50% by 9 d after treatment (DAT). Stomatal conductance to water vapor (gs) declined similarly withANover time for halosulfuron, imazapic, and glyphosate treatments. However,gsof MSMA-treated plants was near 95% of the untreated control, whereasANdeclined to 35% 11 DAT. At 11 DAT, all aboveground biomass was removed, and plants were returned to the greenhouse, and regrowth was determined after an additional 14 d. Yellow nutsedge regrowth for halosulfuron, imazapic, glyphosate, and MSMA was below 5% of the untreated control and was not statistically different. However, regrowth from bentazon was 44% of the control. Therefore, bentazon was the least effective herbicide tested, whereas halosulfuron and imazapic were most effective for yellow nutsedge control.