Influence of glyphosate on corn hybrid tolerance to tolpyralate plus atrazine

This study consisting of six field experiments was conducted in 2018 and 2019 to evaluate the tolerance of four corn hybrids (P9998AM, P9840AM, DKC42-60RIB, and DKC43-47RIB) to the tank mix of tolpyralate + atrazine with a commercial glyphosate formulation. At 1 wk after application (WAA), two corn hybrids (P9998AM and P9840AM) exhibited more injury from tolpyralate + atrazine (2x rate) applied alone and in combination with glyphosate than DKC42-60RIB and DKC43-47RIB; however, all corn hybrids responded similarly with respect to visible injury 2, 4, and 8 WAA, stand loss, and yield. Application of tolpyralate + atrazine or glyphosate + tolpyralate + atrazine at the 2x rate caused greater corn injury (up to 27%) than tolpyralate + atrazine or glyphosate + tolpyralate + atrazine at the 1x rate (up to 8%) at 1 WAA. The addition of commercial glyphosate with tolpyralate + atrazine did not enhance injury symptoms. Results of this study show that there is a wide margin of corn safety with tolpyralate + atrazine applied alone and in combination with a commercial formulation of glyphosate.