Abstract

Tolpyralate, an HPPD (4-hydroxyphenyl-pyruvate dioxygenase) inhibitor, is a relatively new herbicide for weed control in corn. Field studies were conducted in 2015 and 2016 to evaluate the effective dose of tolpyralate applied alone or mixed with atrazine for weed control in corn. The treatments included seven rates (0, 5, 20, 29, 40, 50 and 100 g ai ha-1) of tolpyralate applied alone or mixed with a constant rate (560 g ai ha-1) of atrazine. The evaluated weed species were common waterhemp (Amaranthus rudis Sauer), common lambsquarters (Chenopodium album L.), velvetleaf (Abutilon theophrasti Medik), henbit (Lamium amplexicaule L.) and green foxtail (Setaria viridis L.). Overall, POST-application of tolpyralate resulted in 42-100% visual weed control, depending on the weed species and tolpyralate doses. Calculated dose of 19-31 g ai ha-1 (ED90) of tolpyralate applied alone provided 90% visual control of common waterhemp, common lambsquarters, henbit, and velvetleaf. However, addition of atrazine significantly reduced the required dose of tolpyralate to 11-17 g ai ha-1 for the same level of control of these weed species; suggesting a synergy between the two herbicides.

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