You get to the end of the row while shelling corn, and you hit a patch of morning glory vines. The next thing you know you have to stop the combine and spend the next few minutes untangling the vegetation from the headers.
That’s not how most corn growers want to spend their time harvesting corn, but there are steps you can take to help break through the vines and keep moving, according to Dr. Tom Barber, Extension weed scientist with the University of Arkansas System Division of Agriculture.
“This time of year I get a lot of calls on what can we do about these field ends that are covered in morning glory, or if we have an entire field that may have a problem,” said Barber, who spoke on late season corn weed control during the University of Arkansas’ virtual Corn and Cotton Field Day in late October.
“Paraquat or Gramoxone is labeled for harvest aid in corn along with Aim or carfentrazone and sodium chlorate. So those are the three products that we can use as potential harvest aids at the end of the corn season.”
Weed control options
Gramoxone is sold in a two-pound and paraquat and others in a three-pound formulation. The label rate for Gramoxone is two pints per acre plus a nonionic surfactant and for the three-pound material 1.33 pints with a surfactant. Growers can also mix those products with three to six pounds of sodium chlorate.
“The second option, which is the one most go to in a corn scenario, is Aim,” he said. “So with Aim we need to look at two ounces per acre plus 1 percent crop oil. And for good measure, I throw in at least three pounds of sodium chlorate.
“In a corn crop scenario, most of that’s going to go out via airplane. If we're using an airplane to make the application, we can have a lot of crops around the area that are going to be sensitive to paraquat. So we want to be mindful before we recommend a harvest aid in corn or any crop of our surroundings.”
In the Mid-South, corn is typically harvested in late summer before cotton and soybeans and other crops are mature. “Anything that hasn't reached physiological maturity can be susceptible to drift from these harvest aid applications. Aim is probably a little less injurious from a drift standpoint than the paraquat will be.”
Barber said those combinations may not kill all of the morning glory because of the size of the vines and moisture conditions that often occur at the time of corn harvest.
“Our main goal is we want corn to feed through the combine easier and not have vines tangled up in our heads,” he noted. “The idea is we want to ‘brittle’ this vine down to where we can cut through it with our corn head and not have any clogging of our equipment.”
Growers should also be thinking about how to prevent morning glory from becoming a problem that can impede the corn harvest when being able to finish and prepare to harvest the next crop is critically important.
“You know, most growers use and consultants recommend a one-shot program in corn, and I can make a one-shot program very effective for most weeds, especially when I'm protecting yield,” he said. “But that doesn't mean we’re going to have season long protection. So we really need to think about multiple applications or a two-shot program for morningglories.
“Some of the best residuals we have for these morningglory issues are atrazine and products that contain mesotrione or Callisto. So anything with Callisto or mesotrione plus atrazine either in a drop nozzle scenario but in our final post application will give us our best residual control for morningglories.”
To view the presentation, visit https://aaes.uada.edu/videos/2021-weed-control-in-corn/