Horseweed and giant ragweed are competitive, annual weeds that can negatively impact crop yield. Biotypes of glyphosate-resistant (GR) giant ragweed and horseweed were first reported in 2008 and 2010 in Ontario, respectively. GR horseweed has spread throughout the southern portion of the province. The presence of GR biotypes poses new challenges for soybean producers in Canada and the United States. Halauxifen-methyl is a recently registered selective herbicide against broadleaf weeds for preplant use in corn and soybean. There is limited literature on the efficacy of halauxifen-methyl on GR horseweed and giant ragweed when combined with currently registered products in Canada. The purpose of this study was to determine the effectiveness of halauxifen-methyl applied alone and tank-mixed to control GR giant ragweed and GR horseweed in glyphosate and dicamba-resistant (GDR) soybean in southwestern Ontario. Six field experiments were conducted separately for each weed species over 2018 and 2019. Halauxifen-methyl applied alone offered 72% control of GR horseweed at 8 wk after application (WAA). Control was improved to >91% when halauxifen-methyl applied in combination with metribuzin, saflufenacil, chlorimuron-ethyl + metribuzin, and saflufenacil + metribuzin. At 8 WAA, halauxifen-methyl provided 11% control of GR giant ragweed, and 76% to 88% control when glyphosate/2,4-D choline, glyphosate/dicamba, glyphosate/2,4-D choline + halauxifen-methyl, and glyphosate/dicamba + halauxifen-methyl were used. We conclude that halauxifen-methyl applied preplant in a tank-mixture can provide effective control of GR giant ragweed and horseweed in GDR soybean.

中文翻译：

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植前施用甲基卤草醚防治大豆中抗草甘膦马草和豚草

马草和巨型豚草是具有竞争力的一年生杂草，会对作物产量产生负面影响。抗草甘膦 (GR) 巨型豚草和马草的生物型分别于 2008 年和 2010 年在安大略省首次报道。GR马草已遍布该省南部。遗传资源生物型的存在给加拿大和美国的大豆生产商带来了新的挑战。Halauxifen-methyl 是一种最近注册的针对阔叶杂草的选择性除草剂，用于玉米和大豆的种植前使用。与目前在加拿大注册的产品结合使用时，关于 halauxifen-methyl 对 GR 马草和巨型豚草的功效的文献有限。本研究的目的是确定在安大略省西南部的抗草甘膦和麦草畏 (GDR) 大豆中单独使用和桶混使用甲基卤代芬防治 GR 巨型豚草和 GR 马草的有效性。在 2018 年和 2019 年，对每种杂草分别进行了六次田间试验。单独施用的 Halauxifen-methyl 在施用后 8 周（WAA）提供了 72% 的 GR 杂草控制。当halauxifen-methyl 与metribuzin、saflufenacil、氯嘧磺隆+metribuzin 和saflufenacil + metribuzin 联合应用时，控制提高到>91%。在 8 WAA，halauxifen-methyl 对 GR 巨型豚草的控制率为 11%，当草甘膦/2,4-D 胆碱、草甘膦/麦草畏、草甘膦/2,4-D 胆碱 + halauxifen-methyl 时，控制率为 76% 至 88%，和草甘膦/麦草畏 + halauxifen-methyl 被使用。