Plant Growth Regulator (HG 4) Herbicide Injury in Corn
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.
Plant growth regulator injury mainly occurs from the direct application of herbicides like 2,4-D and dicamba to corn after the label-indicated cutoff timing. Symptoms include malformed root systems, especially brace roots, onion-leafing or tightly wrapped whorls. Application of growth regulators can also cause plant stunting and stems to become brittle which can lead to plant leaning and “green snap” where corn stems snap off due to lateral forces such as high winds. Shoots may fail to emerge from the soil properly following preemergence applications. Enlist corn hybrids have reduced sensitivity to 2,4-D.
2,4-D injury to corn.
Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Dicamba injury to corn.
Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
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.
2,4-D injury to corn. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Dicamba injury to corn. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
2,4-D injury to corn. By Adam Sisson.
2,4-D injury to corn. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
2,4-D injury to corn. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
Dicamba injury to corn. By Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
2,4-D injury to corn. By Adam Sisson.
Gallery images courtesy Adam Sisson, Iowa State University and Cal Shumway, Bob Scott, and John Boyd, www.uada.edu.
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