PPDL Picture of the Week

July 20, 2018

Dicamba Injury on Soybean

Joe Ikley, Weed Science Program Specialist, Department of Botany and Plant Pathology, Purdue University

With the commercialization and widespread adoption of dicamba-tolerant soybeans in Indiana, we have received record numbers of complaints about potential dicamba injury on soybeans over the last two summers. While most of these samples have been confirmed for dicamba damage, there have been several that were injured by some other herbicide. One source of confusion with regards to dicamba injury comes from widespread use of the terms “cupping” and “puckering”.

The terms “cupping” and “puckering” are often used to describe dicamba injury on soybean. One problem with those terms are that they can be subjective, and many herbicides can cause “cupping” or “puckering” on soybean leaves. In order to clear up some confusion, this article will examine a few of the more specific symptoms to look for if you suspect dicamba injury on soybeans. The symptoms described here will be found on new trifoliates that emerge after dicamba exposure, as dicamba moves systemically within the plant and we don’t often see damage immediately after application except in cases of exposure to a high dose of dicamba.

Dicamba will cause parallel orientation of soybean veins. This parallel venation is even observed after light exposure to dicamba, though in those cases, it is often found only near the tip of the soybean leaf. The best way to look for this parallel venation is to look at the underside of soybean leaves. The other important symptom, which is unique to dicamba compared to injury from other commonly used Group 4 herbicides like 2,4-D or clopyralid, is a discolored leaf tip. The coloration can range from white or cream-colored to a darker tan color. 

It is always important to look at multiple plants, and multiple trifoliates on plants to confirm injury symptoms. Depending on exposure rate, timing, and number of exposure events, there can be a wide variety of symptoms present on an individual plant. However, two symptoms you will find on soybean leaves that emerge after exposure to dicamba will be those parallel leaf veins and the discolored leaf tip. If you suspect dicamba injury and would like confirmation, plant samples can always be sent to the Purdue Pest and Diagnostic Lab for confirmation of symptoms.

​Click image to enlarge

Picture 1. Injury from a Group 15 herbicide. Some may use the terms “cupping” or “puckering” to describe this injury.

Picture 2. Injury from dicamba exposure. This plant shows the “cupping” symptom, but one should still look at leaf vein orientation and check for the discolored leaf tip.

Picture 3. Normal net orientation of soybean veins.

Picture 4.  Parallel orientation of soybean veins after dicamba exposure. Notice the light-tan leaf tip.

Picture 5. Range of injured and non-injured leaves due to dicamba exposure.