Optimizing Diluent Volume Improves Johnsongrass Control in Sugarcane (Saccharumsp.) with Asulam

Field studies were conducted in second-ratoon crops of sugarcane infested with rhizome johnsongrass to determine the effects of aqueous diluent volumes ranging from 47 to 561 L ha-1on the performance of asulam. Trend analyses of johnsongrass recovery, based on panicle numbers late in the growing season, indicated a quadratic response with panicle numbers being lowest when asulam at 2.8 kg ai ha-1was applied in a diluent volume approaching 187 L ha-1. The response was similar regardless of whether droplet size or number was altered to obtain these diluent volumes. Differences in late-season johnsongrass control were reflected in harvested sugarcane stalk populations and net cane yields. In greenhouse studies, johnsongrass plants were thoroughly washed with water 24 h after treatment with asulam at 2.8 kg ha-1at water volumes ranging from 47 to 374 L ha-1. Asulam absorption, as evidenced by reduction in the growth of johnsongrass, was higher when surfactant was included, but was not affected by diluent volumes in the range evaluated.