Plant Growth Regulator (HG 4) Herbicide Injury in Soybean
Published: 09/08/2023
Plant growth regulators, or Group 4 herbicides, mimic the activity of the growth-regulating hormone auxin. Therefore, these herbicides are also referred to as synthetic auxins. These herbicides are translocated to the plant growing point, resulting in symptoms appearing on the newest leaves after exposure. Multiple herbicides within this class are used in row crops, pasture, forages, and non-crop areas. Dicamba and 2,4-D are commonly used in corn and resistant soybean varieties. Clopyralid is applied in corn and can carry over in dry conditions. Quinclorac and florpyrauxifen-benzyl are used in rice fields that commonly neighbor soybean fields in the Mid-South. Picloram and aminopyralid are used in pasture and forage production and can carry over to soybean in a couple of ways. First, if the pasture is converted to soybean production the following year, herbicide residues may persist and injure soybeans. Second, herbicide residues are likely to persist on treated hay. If treated hay is provided as feed to cattle grazing in the field or if manure from cattle that have consumed treated hay is applied to the field, soybean injury can occur. Some herbicides, including aminopyralid, can be applied to dry fertilizer which can lead to contamination of a fertilizer cart or tender.
Dicamba drift on soybean.
Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
2,4-D injury to soybean.
Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Growth regulators cause strapping or cupping of new leaves in sensitive soybean. It can be difficult to determine which specific Group 4 herbicide caused injury. 2,4-D has symptoms of a strapped leaf appearance, and the leaves appear longer and thinner. 2,4-D can also cause the production of adventitious roots along the soybean stem when exposure occurs at low rates. Dicamba is often associated with leaf cupping and veins that are parallel and stretched at the tips of leaves. At low doses, which commonly occur with physical drift during application and/or temperature inversion, volatility, or tank contamination, all three leaflets will be injured similarly. In severe cases, epinasty, or twisting of the stems, may occur within a few days of application. Depending on the stage at which the soybean is exposed and which specific Group 4 herbicide, it can take anywhere from a couple of days to a couple of weeks before symptoms appear. The herbicide is translocated to the developing tissue. Plant growth regulator herbicide injury can sometimes be confused with symptoms caused by Group 15 herbicides and viruses.
See the Herbicide Classification Chart from Take Action for herbicide selection information to help slow the development of resistant weeds.
Prepared and reviewed by Dr. Thomas (Tommy) Butts, University of Arkansas; Dr. Joe Ikley, North Dakota State University; the Integrated Pest Management Program at Iowa State University; Dr. Sarah Lancaster, Kansas State University; Dr. Travis Legleiter, University of Kentucky; and Dr. Rodrigo Werle, University of Wisconsin-Madison.
Dicamba injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Quinclorac injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Quinclorac injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
2,4-D injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
2,4-D injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Aminopyralid injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Triclopyr injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Plant growth regulator injury to soybean. By Kristine Schaefer.
Triclopyr injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Dicamba injury to soybean. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Gallery images courtesy Kristine Schaefer, Iowa State University and Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
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