|BETHKE, RACHEL - Michigan State University|
|SPRAGUE, CHRISTY - Michigan State University|
|PENNER, DONALD - Michigan State University|
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2012
Publication Date: 1/14/2013
Citation: Bethke, R.K., Molin, W.T., Sprague, C., Penner, D. 2013. Evaluation of the interaction between glyphosate and glufosinate. Weed Science. 61(1):41-47.
Interpretive Summary: Farmers have observed less than expected weed control when combinations of glyphosate and glufosinate have been used. Scientists from Michigan State University and USDA-ARS-CPSRU conducted a study to determine weed control and herbicide interactions in the form of synergisms and antagonisms in four important weeds. Antagonisms in weed control were observed between glyphosate and glufosinate indicating loss in herbicide activity when used in combination on certain weeds. These results describe unexpected consequences of herbicides mixtures which will allow farmers to make more informed weed control decisions when selecting herbicide programs.
Technical Abstract: Crops engineered to provide resistance to more than one herbicide with different mechanisms of action creates new opportunities for control of resistant weeds. However, unexpected interactions may develop especially for herbicides not generally used in tank mix combinations. The objectives of this study were to evaluate weed control, to determine herbicide interactions, and fluorescence responses obtained with glyphosate and glufosinate on three annual weeds prevalent in Michigan cropping systems; giant foxtail, common lambsquarters, velvetleaf and the perennial weed, Canada thistle. Field studies to determine herbicide interactions resulted in synergism only at the highest rates of glyphosate and glufosinate in 2008. Early synergism (7 DAT) was observed in the field at several combined rates for common lambsquarters and velvetleaf in 2009, and in the greenhouse for giant foxtail. Differences between years were perhaps due to the effect of environment on herbicide absorption and translocation. Antagonism was observed in the field in 2009 for velvetleaf, common lambsquarters and giant foxtail especially at 840 g ae\ha glyphosate and 118 g ai/ha glufosinate at 28 DAT. Antagonism was also observed in the greenhouse for giant foxtail and Canada thistle at 28 DAT. Fluorescence measurements on Canada thistle in the greenhouse showed that glufosinate and glufosinate plus glyphosate acted rapidly to quench electron transport of PSII system of photosynthesis, and the fluorescence characteristics of the glyphosate/glufosinate combinations were indistinguishable from glufosinate alone.