Tolpyralate + Atrazine Applied Preemergence Provides Residual GR Canada Fleabane [&amp;lt;i&amp;gt;Conyza canadensis&amp;lt;/i&amp;gt; (L.) Cronq.] Control Similar to Current Industry Standards

Nicole M Langdon,Nader Soltani,Darren E Robinson,David C Hooker,Alan J Raedar,Peter H Sikkema

doi:10.4236/as.2020.114024

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.

Highlights

Canada fleabane [Conyza canadensis (L.) Cronq.] is a widely adapted broadleaf weed that is native to North America [1]
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

Summary

Introduction

Canada fleabane [Conyza canadensis (L.) Cronq.] is a widely adapted broadleaf weed that is native to North America [1]. As a summer or winter annual, Canada fleabane has become a troublesome agricultural weed. Germination of seeds can occur throughout the year if temperatures reach the base temperature for germination (8.0 ̊C - 9.5 ̊C) and flowering occurs throughout the summer and the latter part of the fall [2]. Seeds that germinate in the fall and over-winter as rosettes establish without competition from neighbouring weeds, which is a competitive advantage over other summer annual weeds [1]. The first confirmed GR Canada fleabane population was discovered in 2001 in a GR soybean field near Delaware, USA that received glyphosate applications for three consecutive years [4]. In 2010, the first GR Canada fleabane population was discovered in Ontario in Essex County, and by 2015, GR populations were found in 30 counties across southern Ontario from the Michigan to the Quebec border [5]

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