Spray solution pH and soybean injury as influenced by dicamba and 2,4-d herbicide formulation and spray additives

Sarah Striegel, former graduate student in the Cropping Systems Weed Science program, Department of Agronomy, University of Wisconsin-Madison, had her first manuscript recently published in Weed Technology. Herein we provide the highlights of her latest publication and access to two technical articles for download and circulation to our clientele.

Original research article: Striegel S, Oliveira MC, Arneson N, Conley SP, Stoltenberg DE, Werle R (2020) Spray solution pH and soybean injury as influenced by synthetic auxin formulation and spray additives. Weed Technol. DOI: 10.1017/wet.2020.89


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.

Research Objectives

The main objectives of S. Striegel’s research were to (1) investigate the roles of synthetic auxin herbicide formulation, glyphosate, and spray additives on spray solution pH; and (2) 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). 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 in low-tunnel field volatility experiments. Greater soybean injury in field experiments was associated with high air temperatures (maximum, >85 F) and low wind speeds (mean, 0.7–3 mph) during the 48 h after treatment application. The two dicamba formulations (diglycolamine salt with VaporGrip® [Xtendimax with VaporGrip® herbicide] and sodium salt [Status herbicide]) 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 choline treatments.

Technical articles for download and circulation to our clientele (PDF files):

Acknowledgements These technical articles have been developed by Nick Arneson (UW-Madison Weed Science Outreach Specialist), Sarah Striegel (Former UW-Madison Weed Science Graduate Student) and Dr. Maxwel Oliveira (UW-Madison Weed Science Research Associate).

Funding for S. Striegel’s graduate research assistantship was provided by Bayer Crop Science and the R.Gordon Harvey Distinguished Graduate Fellowship. Dr. Werle served as S. Striegel’s major advisor; Drs. Conley and Stoltenberg served as advisory committee members. The authors would like to thank the University of Wisconsin-Madison Cropping Systems Weed Science research group and the Arlington Agricultural Research Station staff for their technical assistance in establishing the experiments.