In North Dakota we now have three crops where both glyphosate (ex RoundUp Powermax) and glufosinate (ex Liberty) can be applied in the same season. These crops are corn, soybeans, and canola. Since glyphosate is highly mobile in plants and glufosinate is a contact product, there is potential for antagonism on the plant surface. In 2018 we started to investigate the impact of adding glyphosate to glufosinate. In 2019 we tested combinations in three locations of ND with a variety of weed species. In each of these experiments we optimized the application for glufosinate (ex >15 GPA spray volume), which would be the recommendation. In 2019 we also tested combinations of glyphosate and glufosinate with Enlist One and Enlist Duo.

The weed species response varied. Shepard’s purse, common ragweed and redroot pigweed were controlled by all treatment combinations. Green foxtail control was initially good with all treatment combinations, however, by 21 days after application the presence of glufosinate caused a mild reduction in control compared to glyphosate alone. Yellow foxtail control was not affected by the combination of products, it was simply less in treatments without glyphosate. Kochia control was negatively impacted by the combination of products. This is the one case where both products applied alone performed better than the combination. In fact, when adding Enlist products, Enlist Duo was better without glufosinate than with. In all other cases Enlist Duo was a neutral or positive addition.

Wild buckwheat control was enhanced by the combination of the two products. When glufosinate was applied alone, it quickly burned the leaves of wild buckwheat, by the end of the trial the buckwheat had recovered. Glyphosate alone was very slow to control buckwheat, but by the end finished better than glufosinate. When the were added together it was the best of both worlds. The buckwheat was quickly burned back and by the end of the trial the combination performed better than either product alone. Glufosinate with Enlist Duo or Enlist One provided an even larger benefit to buckwheat control at 7 days after application, but was similar to glyphosate plus glufosinate by 21 days.  

In short, there was less antagonism than expected when using these combinations, however, each weed species had a unique response to the products. These combinations may be highly effective when used to manage herbicide resistance, but scouting for escapes will be necessary. Generally these escapes were not detectible until 2 weeks following application.

Table 1. Weed species of interest while testing combinations of glyphosate, glufosinate, and Enlist.

Mike Ostlie, Ph. D.
Mike.Ostlie@ndsu.edu
Research Agronomist