Submitted to: Weed Biology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/6/2005
Publication Date: 9/1/2005
Citation: Molin, W.T., Hirase, K. 2005. Effect of surfactants and simulated rain on the efficacy of engame formulation of glyphosate on seedling johnsongrass, prickly sida and yellow nutsedge. Weed Biology and Management 5:123-127. Interpretive Summary: Modification of herbicide formulations with adjuvants can improve herbicide activity. The effects of surfactants and simulated rain were investigated on the efficacy of Engame and Roundup Ultramax formulations of glyphosate on seedling johnsongrass (Sorghum halepense L.), prickly sida (Sida spinosa L.) and yellow nutsedge (Cyperus esculentus L.). This research was performed at SWSRU farm in Stoneville, MS, from 2002 to 2004. The research shows that certain surfactants increase the efficacy of glyphosate products and improve their rainfastness on important weed species. This shows that the full potential of glyphosate products has not been attained. This knowledge could lead to lower costs of herbicide application to farmers and lower the pesticide load on the environment which could make farming more profitable.
Technical Abstract: The effects of surfactants and simulated rain were investigated on the efficacy of Engame and Roundup Ultramax formulations of glyphosate on seedling johnsongrass (Sorghum halepense L.), prickly sida (Sida spinosa L.) and yellow nutsedge (Cyperus esculentus L.). Flame surfactant provided the greatest enhancement of Engame activity 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. Engame and Roundup Ultramax activity on johnsongrass were similar with rain, and rain occurring between 5 and 30 minutes after treatment diminished their activity to less than 38 % control. With the addition of Flame surfactant, Engame activity on johnsongrass increased such that 50 and 80 % control were realized even with rain occurring between 5 and 15 minutes after treatment, respectively. Engame and Roundup Ultramax provided better control of prickly sida than johnsongrass following a rain event. Addition of Flame surfactant to Engame did not enhance 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 differential species tolerance to Engame, Engame plus Flame, and Roundup Ultramax, as well as differential responses to addition of surfactant.