Effects of surfactants and simulated rainfall on the efficacy of the Engame formulation of glyphosate in johnsongrass, prickly sida and yellow nutsedge

Abstract

The effects of surfactants and simulated rain were investigated on the efficacy of Engame and Roundup Ultramax formulations of glyphosate on johnsongrass (Sorghum halepense L.), prickly sida (Sida spinosa L.) and yellow nutsedge (Cyperus esculentus L.). Flame surfactant provided the greatest enhancement of Engame efficacy and the effect was species‐dependent. Flame enhanced the activity of Engame on johnsongrass and yellow nutsedge but not on prickly sida. Engame and Engame plus Flame were more active than Roundup Ultramax on a glyphosate acid‐equivalent basis on johnsongrass without rain, and on yellow nutsedge with or without rain. The Engame and Roundup Ultramax activities on johnsongrass were similar with rain, and rain occurring between five and 30 min after treatment diminished their activities to < 38% of the control. With the addition of Flame surfactant, Engame activity on johnsongrass increased, such that 50% and 80% of the control were realized, even with rain occurring between five and 15 min after treatment, respectively. Engame and Roundup Ultramax provided better control of prickly sida than of johnsongrass following a rain event. The addition of Flame surfactant to Engame did not enhance the activity on prickly sida. Yellow nutsedge control with Engame and Engame plus Flame was greater than with Roundup Ultramax and rain had little effect on control regardless of the length of the rain‐free period. These results demonstrated that the activities of Engame, Engame plus Flame and Roundup Ultramax were species‐dependent and surfactant‐dependent.