Dicamba and 2,4-D are the most common members of a group of herbicides that mimic naturally occurring plant growth regulators. These herbicides overload a plant’s growth-regulating system. Sensitive crops exposed to drift levels of dicamba and 2,4-D drift may show distorted growth in the leaves, leaf petioles, or stems. Symptoms of drift damage can show up within hours if plants are growing quickly, or within a few days under slower growing conditions.
Dicamba and 2,4-D are the most common members of a group of herbicides that mimic naturally occurring plant growth regulators. These herbicides overload a plant’s growth-regulating system. Sensitive crops exposed to drift levels of dicamba and 2,4-D may show distorted growth in the leaves, leaf petioles, or stems. Symptoms of drift damage can show up within hours if plants are growing quickly, or within a few days under slower growing conditions.
The symptoms and severity of dicamba and 2,4-D drift can vary greatly between species. Watch for cupped leaves (Figure 2a and 3) or leaves that become chlorotic (on leaf tissue or veins), narrowed, or develop parallel veination (Figure 2b), stunted growth (Figure 3), necrosis (tissue death), delayed or uneven flowering/ fruit set, (Figure 4), twisted growth on stems and petioles, adventitious root development (Figure 5), and reduced yield.
We’ve talked about dicamba and 2,4-D together, but they are two distinct chemicals. A plant’s response will not necessarily be the same for both. For example, snap beans and lima beans are more sensitive to dicamba than to 2,4-D. In grapes, low concentrations of both herbicides can cause stem twisting and leaf droop, but dicamba more typically causes cupped leaves in grapes, while narrow leaves with parallel veins (strapping) is a symptom of 2,4-D damage in grapes (Figure 2). Other species may show different signs of damage. There is too much variation between species to make broad generalizations. University of California IPM has a searchable photo gallery of common crops injured by sub-lethal doses of herbicides. University of Missouri also has an excellent collection of photos from dicamba and 2,4-D drift sensitivity trials which includes a variety of woody and herbaceous specialty crops. (See Resources for other helpful links.)
While tools like these can be helpful, most growers will need to consult a professional for a final diagnosis. If a state pesticide regulator cannot be consulted quickly, an extension or university employee, crop consultant, or farmer advocacy organization may be able to suggest professionals or laboratories that can help. See our related fact sheet on responding to and documenting suspected drift damage. It is important to review these steps before drift damage happens.
This publication is a product of the North Central IPM Center working group on Herbicide-Drift Risk Management, with support from the USDA National Institute of Food and Agriculture through agreement 2018-70006-28884.
Reference to any commercial products or trade names implies no discrimination or endorsement by the North Central IPM Center or any of the contributing authors or their universities. Nor does this document constitute legal advice. Always seek legal advice from a professional who is knowledgeable in current agricultural law in your state.
Cassandra Brown, Horticulture and Crop Science, The Ohio State University
Stephen Meyers, Horticulture & Landscape Architecture, Purdue University
Mary Ann Rose, Pesticide Safety Education Program, The Ohio State University
Douglas Doohan, Horticulture and Crop Science, The Ohio State University
The following individuals reviewed part or all of this fact sheet: Bill Johnson, Purdue University; Bryan Young, Purdue University; Aaron B. Wilson, Byrd Polar and Climate Research Center; Cathy Herms, The Ohio State University
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Office of Indiana State Chemist and Seed Commissioner. 2019, Nov 13. OISC Announces 2020 Dicamba Restriction. https://www.oisc.purdue.edu/pesticide/pdf/dicamba_24c_press_release_111319.pdf
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