Soybean Pest Beat: If leaves turn off-color, don’t panic — consider what you can do instead.
May 30, 2018
The local dealer sprayed my soybeans. They killed the weeds, but some leaves turned a bit off-color for a while. New leaves seem to be OK. Am I likely to see a yield decrease? Should I have the dealer come out now in case there is an issue later? Why did some leaves turn color?
The panel of Indiana certified crop advisers answering this question includes Don Burgess, agronomist with A&L Great Lakes Labs, Fort Wayne; Jesse Grogan, agronomist with Ag Reliant Genetics, Lafayette; and Bryan Overstreet, Purdue University Extension ag educator in Jasper County.
Burgess: If you’re unsure what was sprayed on your soybean field or are unfamiliar with the effects of those products on your crop, it would be a good idea to contact the dealer to come investigate the situation. Many herbicides and spray adjuvants can cause burning or discoloration of the foliage with no real effect on yield. The use of glyphosate for years as our primary postemergence herbicide option on soybeans in the Roundup Ready system has led many of us to forget that fact. Glyphosate alone generally doesn’t cause any crop response.
If a significant injury has occurred, it’s important to investigate the situation in a timely manner. This will make it easier to properly diagnose the situation, collect samples or document injury in case there is an issue that may need to be addressed later.
Grogan: Herbicides in the ALS inhibitor site-of-action family, which is Class 2, or the PPO inhibitor site-of-action family, which is Class 14, will cause some temporary injury to soybean leaves. It depends upon application rate, growth stage and weather conditions at application time. Injury is more common in hot and humid weather. A yield decrease is usually not a concern, despite how bad it looks a few days to even a week after application.
New growth indicates injury was temporary and not permanent. It’s probably not an issue for the dealer to visit unless you see extreme injury and stunting. Leaves turn off-color or show a “bronzing” color due to contact injury of the herbicide. Full recovery from injury will require three to four weeks with no yield loss.
Overstreet: I would confirm what products, adjuvants and carrier the applicator sprayed, and what they sprayed just prior to your field. Odds are that if new leaves look fine, there should be no yield loss.
Several of the postemergence herbicide and adjuvant combinations will discolor some leaves with no damage to the plant. Over the past decade we have gotten used to Roundup Ready and LibertyLink systems that didn’t ding beans. With weed pressure today, we’ve reverted to traditional herbicide programs that may discolor the crop.