Evaluation of the fit of Tolpyralate for Weed Management in Field Corn (Zea mays L.) in Ontario

Thirty-six experiments were conducted over two years (2018, 2019) to evaluate tolpyralate, a benzoylpyrazole 4-hydroxyphenyl-pyruvate dioxygenase inhibitor, for weed management in corn in Ontario. The importance of adjuvants (MSO and UAN) with tolpyralate + atrazine and the influence of Roundup Weathermax® was determined for control of nine annual weed species, glyphosate-resistant (GR) Canada fleabane and GR waterhemp. Optimal control was achieved with tolpyralate + atrazine + MSO and when tolpyralate + atrazine was co-applied with Roundup Weathermax®. Tolpyralate and tolpyralate + atrazine has residual activity on GR Canada fleabane, comparable to current industry standards. Three weed species exhibited a time-of-day effect to tolpyralate + atrazine, although, consistent control was achieved regardless of application time. Corn injury was greatest from tolpyralate + atrazine when applied at the 2X rate alone and/or co-applied with glyphosate at 1 WAA; there was no further increase in corn injury when co-applied with glyphosate.