Here’s another way that 2020 could be the year that keeps on giving — by providing another headache through yet another unintended consequence. The derecho that ravaged the Midwest in August hit Iowa hardest, but crops also were damaged in Illinois, Indiana and other states. Where corn went down and not all ears were harvested, volunteer corn in soybeans could be a bigger-than-normal concern in 2021.
Modern corn heads helped gather most of the corn in all but the hardest-hit areas. That’s the plus side. “The fall was dry, though, in many areas, and most corn left behind likely didn’t sprout and die by freezing,” says Bill Johnson, Purdue University Extension weed control specialist. “When we have a late, wet fall, a lot of what would be volunteer corn the next year germinates, but that didn’t happen this time.”
If you had cornfields where lodging was an issue in 2020, Johnson recommends going to soybeans in 2021. “Going back to corn just wouldn’t be a good idea,” he says. “So many of the hybrids carry resistance to glyphosate and/or glufosinate that there is just no good way to take volunteer corn out of corn.”
Control corn in soybeans
You have options in soybeans, and if you expect volunteer corn to be an issue, plan and be ready for it, Johnson says. Soil-applied products such as Scepter, Classic and Pursuit will suppress volunteer corn. You can follow up by adding a postemergence grass herbicide, he says. Assure, Select and Fusion or the generic equivalents will take out volunteer corn if sprayed in a timely fashion and applied at labeled rates.
In the past, if it’s just a stalk here and there, some farmers haven’t worried about volunteer corn and haven’t gone to the expense of adding a postemergence grass product to kill it. Remember, glyphosate, which does a good job on other grasses, likely won’t control volunteer corn.
One argument some growers make is that volunteer corn seldom produces many kernels. That means few, if any, corn kernels will go into the combine hopper.
“There are two solid reasons for taking out volunteer corn in soybeans,” Johnson says. “First, it will compete with soybeans for moisture and nutrients. There can be a yield impact if it is thick enough.
“The reason many forget is that if you let it go, corn rootworms can feed on the roots. Even if it was rootworm-resistant corn, there may not be enough protein there to kill rootworm larvae. If they feed, survive and reproduce, it potentially increases the rate of building resistance to various rootworm control events used in hybrids. If you have volunteer corn in the field, it really needs to come out.”