Influence of Surfactants on the Toxicity of Asulam to Johnsongrass (Sorghum halepense) and Sugarcane (Saccharumsp.)

The influence of surfactant type and concentration on the efficacy of asulam {methyl [(4-aminophenyl) sulfonyl] carbamate} for controlling rhizomatous johnsongrass [ Sorghum halepense (L.) Pers. # SORHA] was evaluated in field and greenhouse studies. Under field conditions, nonoxynol (9 to 10 POE) [α-lp-nonylphenyl)- w -hydroxypoly (oxyethylene)] applied at concentrations of 6% (v/v) with asulam at 2.8 kg ai/ha reduced rhizomatous johnsongrass biomass by 35%, with no consistently significant difference in asulam's performance between surfactant concentrations of 0 and 3% (v/v) being observed. Asulam applied with nonoxynol at concentrations of 3 and 6% (v/v) reduced sugarcane ( Saccharum interspecific hybrids) yields and significantly offset any advantages from increased johnsongrass control. In greenhouse studies, where johnsongrass foliage was washed either 0, 1, 6, 24, or 48 h after treatment (HAT), the degree of johnsongrass control with asulam was generally not affected by the type of surfactant (paraffin-base petroleum oil-surfactant blend or alcohol-surfactant-water mixture) used. At least 48 h was needed to insure adequate basipetal translocation, hence maximum inhibition of rhizome regrowth with asulam applied alone. Increasing the surfactant concentration shortened this interval to 48 h (0.25%) to 24 h (0.5 to 1%) to 6 h (3%) to 1 h (6%).