Current recommendations for the control of glyphosate-resistant horseweed [Conyza canadensis (L.) Cronquist var. canadensis] in soybeans [Glycine max (L.) Merr.] consist of comprehensive herbicide programs, which often include herbicide applications outside the soybean growing season. Integration of cover crops with herbicides could potentially improve C. canadensis control and allow for a reduction in herbicide inputs. Two separate field studies were conducted from 2016 through 2018 with the objectives of: (1) determining the effect of planting date and seeding rate of a cereal rye (Secale cereale L.) cover crop on C. canadensis population density and control in the subsequent soybean crop; and (2) determining whether the cover crop could replace a fall herbicide treatment or allow for a reduction in the use of spring-applied residual herbicides. There was no effect of rye planting date, late September versus late October, on C. canadensis density in either study. In 2016 to 2017, C. canadensis density was greater in the absence of a rye cover crop in both studies, but otherwise not affected by seeding rates of 50 versus 100 kg ha−1. In the 2017 to 2018 season, the presence of rye resulted in an increased C. canadensis density in the spring residual herbicide study (Study I), and had no effect in the fall herbicide study (Study II). Conyza canadensis densities were lowest in the treatments where a comprehensive spring residual or fall herbicide treatment had been applied, averaged over rye planting date and seeding rate. Earlier-planted rye at a higher seeding rate produced the most biomass but did not result in lower C. canadensis densities. These results suggest that cereal rye planted at a density of 50 kg ha−1 as a cover crop before no-till soybeans may be sufficient to reduce glyphosate-resistant C. canadensis plant density, but cannot be relied upon to reduce the need for fall herbicide treatments and spring residual programs.

中文翻译：

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谷物黑麦覆盖作物与除草剂相结合对免耕大豆中抗草甘膦马草（Conyza canadensis）的影响

目前控制抗草甘膦马草的建议 [加拿大白粉虱（L.）克朗奎斯特变种。加拿大人] 在大豆中 [最大甘氨酸(L.) Merr.] 包括全面的除草剂计划，其中通常包括在大豆生长季节以外的除草剂应用。覆盖作物与除草剂的结合可能会改善C.canadensis控制并允许减少除草剂的投入。从 2016 年到 2018 年进行了两项独立的实地研究，目的是：（1）确定谷物黑麦的种植日期和播种率的影响（黑麦L.) 覆盖作物C.canadensis后续大豆作物的人口密度和控制；(2) 确定覆盖作物是否可以替代秋季除草剂处理或允许减少春季施用的残留除草剂的使用。黑麦种植日期（9 月下旬与 10 月下旬）对C.canadensis在任一研究中的密度。2016 年至 2017 年，C.canadensis在两项研究中，在没有黑麦覆盖作物的情况下密度更大，但在其他方面不受 50 对 100 公斤公顷播种率的影响-1. 在 2017 年至 2018 年季节，黑麦的存在导致C.canadensis在春季除草剂残留研究（研究 I）中的浓度，而在秋季除草剂研究（研究 II）中没有影响。加拿大白粉虱在应用了全面的春季残留或秋季除草剂处理的处理中，密度最低，平均超过黑麦种植日期和播种率。早播的黑麦以较高的播种量产生最多的生物量，但不会导致较低的生物量C.canadensis密度。这些结果表明，谷物黑麦的种植密度为 50 kg ha-1作为免耕大豆之前的覆盖作物可能足以降低草甘膦抗性C.canadensis植物密度，但不能依靠减少秋季除草剂处理和春季残留计划的需要。