Uptake, translocation, and metabolism of glyphosate, glufosinate, and dicamba mixtures in Echinochloa crus-galli and Amaranthus palmeri.

Background: Echinochloa crus-galli (L.) Beauv. and Amaranthus palmeri S. Wats are two common and problematic weeds prevalent across the Midsouth of the USA. Herbicide absorption, translocation, and metabolism were investigated as potential sources of herbicide antagonism on A. palmeri and E. crus-galli using C-labeled herbicides. Three C-labeled herbicides, glyphosate, glufosinate, and dicamba, were utilized individually in separate experiments.

Results: Uptake of C-glyphosate in E. crus-galli was 15% of the total applied radioactivity for glyphosate/glufosinate (897 + 595 g a.i./a.e. ha ) compared to 25% for glyphosate alone. Similarly, uptake of C-glyphosate in A. palmeri reduced by 10% when applied with glufosinate. Applying glyphosate/dicamba (897/560 g a.e. ha ) reduced C-glyphosate uptake in both species. In the C-glufosinate experiment, both species absorbed less C-glufosinate when mixed with glyphosate compared to glufosinate alone. No metabolic degradation of glyphosate was observed in either species. E. crus-galli metabolized dicamba 23 times faster than A. palmeri. When glufosinate was applied with dicamba, metabolic degradation of C-dicamba was limited in both species. For example, 99.9% of the applied radioactivity was recovered in A. palmeri as the parent compound when C-glufosinate dicamba was applied with glufosinate, compared to 95.7% for dicamba alone.

Conclusion: These findings demonstrate absorption, translocation, or metabolism of dicamba, glufosinate, and glyphosate can be affected by mixing with another herbicide. As mixing two herbicides is often a critical component of resistance management, careful investigation into the performance of these mixtures in the field is needed. © 2020 Society of Chemical Industry.