Justin Petrosino, and agronomist with Stewart Seeds, got more calls and saw more fields with injured soybeans early in the season than he expected. In most cases, the injuries farmers were concerned about linked back to herbicide injury, largely due to what they applied and when they applied it.
"The problem is some growers who are impacted are already talking about dropping residual herbicides next year and going back to just post products on soybeans," he says. "That would be a bad management decision."
Some might call it a knee-jerk reaction – applied residual for first time in years, saw injury, so don't apply residuals ever again!
What they need to do instead, Petrosino says, is understand what happened this year, why it happened, and be willing to follow label directions. One of the big problems he has seen was misuse of herbicides in the PPO inhibitor class. The result is black speckling on leaves of young soybeans.
In many cases the farmer applied a saflufenacil herbicide, such as Sharpen, Verdict or Optill, then a residual product containing flumoioxazin, a Calor chemistry, or sulfentrazone, Authority-type products.
The problem is that the label for the saflufenacil herbicides clearly prohibits the use of other PPO inhibitors for 30 days after application of the first product. The reason is that if you don't wait, you can get a heavy dose of PPO herbicides on the plants. Under certain conditions that can cause injury. At least some people saw those kinds of conditions this year.
The problem with swearing off PPO residuals is that they are great for marestail, waterhemp and lambsquarters – some of the weeds causing the biggest problems. And if the injury occurs early, there is likely to be little effect on yield potential. There are always exceptions and there could be an extreme case where yield potential is damaged, but that's not common, he notes.