Effect of dew and spray volume on the efficacy of control of asulam on fall panicum (Panicum dichotomiflorum)

Asulam controls fall panicum (Panicum dichotomiflorum Michx.), the most troublesome annual grass weed in Florida sugarcane. This study was conducted to evaluate the effect of dew on asulam efficacy on fall panicum control when applied using different spray volumes. Fall panicum 30 cm tall with 0, 50, and 100% dew on leaves equivalent to no dew, moderate dew, and heavy dew, respectively, were treated with asulam at 3,700 g ha^–1 using spray volumes of 94, 140, 187, and 281 L ha^–1. Fall panicum control was rated 28 days after treatment, and aboveground biomass was harvested immediately. The presence or absence of dew and spray volume did not significantly influence asulam efficacy on fall panicum control and aboveground biomass accumulation. Fall panicum was controlled from 89% to 94% at the different dew levels and spray volumes. Heavy dew did not diminish the performance of asulam. The presence of dew on fall panicum foliage probably hydrated the cuticle and aided water-soluble asulam to remain in solution for a longer period, thereby enhancing uptake. The water-holding capacity of fall panicum foliage with the heavy dew and spray volumes was probably not exceeded, resulting in no runoff and no subsequent reduction of control. These results indicate that dew deposition under Florida conditions has no effect on asulam efficacy on fall panicum 30 cm tall or less when applied at commonly used spray volumes of 140 and 187 L ha^–1.