Use of synthetic auxin herbicides has increased across the midwestern United States after adoption of synthetic auxin-resistant soybean traits, in addition to extensive use of these herbicides in corn. Off-target movement of synthetic auxin herbicides such as dicamba can lead to severe injury to sensitive plants nearby. Previous research has documented effects of glyphosate on spray-solution pH and volatility of several dicamba formulations, but our understanding of the relationships between glyphosate and dicamba formulations commonly used in corn and for 2,4-D remains limited. The objectives of this research were to (1) investigate the roles of synthetic auxin herbicide formulation, glyphosate, and spray additives on spray solution pH; (2) assess the impact of synthetic auxin herbicide rate on solution pH; and (3) assess the influence of glyphosate and application time of year on dicamba and 2,4-D volatility using soybean as bioindicators in low-tunnel field volatility experiments. Addition of glyphosate to a synthetic auxin herbicide decreased solution pH below 5.0 for four of the seven herbicides tested (range of initial pH of water source, 7.45–7.70). Solution pH of most treatments was lower at a higher application rate (4× the labeled POST rate) than the 1× rate. Among all treatment factors, inclusion of glyphosate was the most important affecting spray solution pH; however, the addition of glyphosate did not influence area under the injury over distance stairs (P = 0.366) in low-tunnel field volatility experiments. Greater soybean injury in field experiments was associated with high air temperatures (maximum, >29 C) and low wind speeds (mean, 0.3–1.5 m s−1) during the 48 h after treatment application. The two dicamba formulations (diglycolamine with VaporGrip® and sodium salts) resulted in similar levels of soybean injury for applications that occurred later in the growing season. Greater soybean injury was observed after dicamba than after 2,4-D treatments.

中文翻译：

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受合成生长素配方和喷雾添加剂影响的喷雾溶液 pH 值和大豆损伤

除了在玉米中广泛使用这些除草剂外，在采用合成的抗生长素大豆特性后，合成生长素除草剂的使用在美国中西部有所增加。麦草畏等合成生长素除草剂的脱靶运动会对附近的敏感植物造成严重伤害。先前的研究已经记录了草甘膦对几种麦草畏制剂的喷雾溶液 pH 值和挥发性的影响，但我们对玉米和 2,4-D 中常用的草甘膦和麦草畏制剂之间关系的理解仍然有限。本研究的目的是 (1) 研究合成生长素除草剂配方、草甘膦和喷雾添加剂对喷雾溶液 pH 值的作用；(2) 评估合成生长素除草剂用量对溶液 pH 值的影响；(3) 在低隧道田间挥发性试验中，使用大豆作为生物指示剂，评估草甘膦和一年中的施用时间对麦草畏和 2,4-D 挥发性的影响。将草甘膦添加到合成的生长素除草剂中，将测试的七种除草剂中的四种的溶液 pH 降低到 5.0 以下（水源的初始 pH 范围为 7.45-7.70）。大多数处理的溶液 pH 在较高的施用率（4 倍标记的 POST 率）下低于 1 倍率。在所有处理因素中，草甘膦的加入是影响喷雾溶液 pH 值的最重要因素；然而，在低隧道田间挥发性实验中，添加草甘膦并不会影响远距离楼梯下的损伤面积（P = 0.366）。田间试验中较大的大豆损伤与高温有关（最高，>-1) 在治疗应用后的 48 小时内。两种麦草畏配方（二甘醇胺与 VaporGrip®和钠盐）对生长季节后期发生的施用造成相似程度的大豆损伤。麦草畏比 2,4-D 处理后大豆损伤更大。