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.