Bill Johnson, Purdue University weed control specialist, says there are two reasons to take out Roundup Ready volunteer corn. And neither has anything to do with ugly corn. Both reasons relate instead to both short-term and long-term profit potential.
"First, we're looking at yield loss" Johnson says., A Purdue University study in '08 showed that the economic threshold for payback for spraying was less one to two volunteer corn plants per square meter of soybeans. At around 1 volunteer corn plant per acre, yield for soybeans with volunteer corn was significantly lower, by about 2 or more bushels per acre. At four plants per square meter, yield dropped from 54 to 36 bushels per acre.
That's a huge drop just for volunteer corn. Realize, however, that four plants per square meter would be viewed as a relatively thick infestation. Problems such as that would be most likely if corn was down during harvest. Unfortunately, lots of down corn was harvested last fall, due both to high winds in September, and then stalk rot problems for corn not harvested until late October or even into early November.
Leaving corn in the field was the first economic loss. Having it come back as volunteer corn and provide competition against the soybean crop is another immediate money pit. Then there's a third way that volunteer corn could prove harmful, even though it's a long-term problem.
"Most volunteer GMO corn carries BT genes," Johnson says. "Work by Purdue entomologists indicates that the Bt toxin is present at a lower dose.
"They're not sure what that might mean for insect populations that Bt corn controls. But they suspect that over time it could contribute to faster onset of insect resistance." Such resistance may not hit your pocketbook in the short term, but could contribute to losing GMO corn, at least Bt corn, as an effective weapon against insects in the long haul.
One of the problems with volunteer corn is that by the time it's noticeable and unsightly, it's already caused a lot of the short-term economic loss through competition with the soybean crop. That's why Johnson advises keeping a sharp eye out for it early. Mark those fields where you suspect a problem based on harvest losses last fall, and check those very carefully.
"Volunteer corn tends to hide under the canopy early," he says. "We recommend scouting and spraying in a timely manner with a grass herbicide."