Nicole M. Langdon¹, Nader Soltani^1*, Alan J. Raedar², David C. Hooker¹, Darren E. Robinson¹, Peter H. Sikkema¹

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¹ University of Guelph Ridgetown Campus, Ridgetown, Canada.
² ISK Biosciences Inc., Concord, OH, USA.
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Abstract: Tolpyralate is a benzoylpyrazole, 4-hydroxyphenyl-pyruvate dioxygenase inhibitor, and a herbicide registered for use in corn. The efficacy of tolpyralate plus atrazine to provide full-season residual control of glyphosate-resistant (GR) Canada fleabane in corn is not known under Ontario environmental conditions. Five field trials were completed over a two-year period (2018-19) in south-western Ontario on farms with confirmed GR Canada fleabane [Conyza canadensis (L.) Cronq.] populations to determine if tolpyralate + atrazine provides full-season residual control of GR Canada fleabane in corn. Corn injury was less than 10% with all treatments. At 4 weeks after application (WAA), tolpyralate (30 g·ai·ha^−1), tolpyralate (40 g·ai·ha^−1), and atrazine (560 g·ai·ha^−1) controlled GR Canada fleabane 64, 78 and 72%, respectively. A tank mix of tolpyralate + atrazine at both rates improved GR Canada fleabane control to 94%. Saflufenacil/dimethenamid-p, mesotrione + atrazine, and dicamba/atrazine controlled GR Canada fleabane 99, 95 and 92%, respectively. At 8 WAA, tolpyralate (30 g·ai·ha^−1), tolpyralate (40 g·ai·ha^−1) and atrazine (560 g·ai·ha^−1) controlled GR Canada fleabane 83, 88, and 83%, respectively (Table 2). The tank mixes of tolpyralate (30 g·ai·ha^−1) + atrazine (560 g·ai·ha^−1) and tolpyralate (40 g·ai·ha^−1) + atrazine (560 g·ai·ha^−1) controlled GR Canada fleabane 94, and 97%, respectively, 8 WAA which was similar to saflufenacil/dimethenamid-p, mesotrione + atrazine and dicamba/atrazine. There was no treatment difference for corn yield. Based on these results, tolpyralate (40 g·ha^−1), tolpyralate (30 g·ha^−1) + atrazine and tolpyralate (40 g·ha^−1) + atrazine, applied PRE, provided similar control of GR Canada fleabane as current industry standards at 8 WAA.

Keywords: Crop Injury, Density, Efficacy, Glyphosate-Resistant, Horseweed, Marestail, Residual Weed Control, Sensitivity, Weed Control g·ai·ha^-1

Cite this paper: Langdon, N. , Soltani, N. , Raedar, A. , Hooker, D. , Robinson, D. and Sikkema, P. (2020) Tolpyralate + Atrazine Applied Preemergence Provides Residual GR Canada Fleabane [Conyza canadensis (L.) Cronq.] Control Similar to Current Industry Standards. Agricultural Sciences, 11, 417-424. doi: 10.4236/as.2020.114024.

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