Soybeans appearing ‘puckered’ or ‘crinkled’ following high temperatures
Vince M. Davis, Cropping Systems Weed Scientist and Extension Specialist
Temperatures across Wisconsin were in the 90’s and upper 90’s much of last week. Some areas were also in need of rain during the same time. I received calls and emails with concerns about puckered soybean leaves starting at the end of last week through the beginning of this week, (Figure 1). Plant growth regulating herbicides (PGR’s) such as 2,4-D and dicamba used in postemergence corn herbicide programs cause this type of symptomology to sensitive broadleaf weeds and crops. Occasionally, this is observed as an undesirable response when PGR herbicides drift from neighboring fields during postemergence applications. Furthermore, PGR’s are also prone to volatilize under certain weather conditions, and the vapors move off-site affecting sensitive plants hours or even days after application. Lastly, PGR’s can be difficult to clean from application equipment and may contaminate spray applications later made to sensitive crops with the same equipment. To avoid drift, spray when winds are low and preferably blowing away (not toward) sensitive plants and use appropriate application technology. To avoid tank contamination, strictly follow tank cleaning procedures stated on the labels, especially between PGR and soybean applications. Unfortunately there is little control an applicator has to avoid volatility days after an application. All in all, there is no denying that drift, volatility, and tank-contamination of PGR herbicides are all possible scenarios that cause puckered soybeans, and many times one of these scenarios are often the cause. However, that does not rule out other possible causes for the same symptomology to occur. Sometimes when symptoms are observed, it is nearly impossible to blame a PGR herbicide.
There have been several extension articles over the last 12 years discussing the phenomena of crinkled and cupped soybean leaves for reasons other than PGR herbicides. From these other theories were put forth to explain the symptoms, but unfortunately, they are much more difficult to explain or characterize. One thing that is certain, and should be understood, is that PGR herbicides work by mimicking growth regulating compounds that are already produced by plants. Therefore, it is possible for anything that may cause an imbalance in normal hormone levels in actively growing vegetative tissue to be a cause. First of all, there are a few viral infections that will cause this symptomology, but they usually affect certain plants among plants with no symptoms. In many of the situations that raise questions, all the plants in large areas or even whole fields are affected. From reviewing former extension articles and observing plants from these situations, it seems this condition is most likely to occur when soybeans are under stress from heat and/or moisture, and following postemergence applications of translocated herbicides such as glyphosate. Exactly why it occurs is unknown.
The good news is that soybeans have a tremendous ability to regulate seed yield due to long reproductive growth stages. Therefore, if weather conditions improve to support normal soybean growth then it is likely symptoms will subside. How much impact these symptoms cause on yield is more difficult to assess. It is always difficult to say yield is not adversely affected, however, in many cases significant yield penalties should not be expected. To learn more and study pictures of PGR herbicide damage and mimics, there are two great resources to read further: Dicamba Injury Mimics [http://soybean.uwex.edu/library/soybean/grain/Weed_Contol/dicamba2004.pdf.pdf] previously produced by the UW NPM program and Plant Growth Regulator Injury to Soybean [http://weeds.cropsci.illinois.edu/extension/factsheets/PGR.pdf].