Glenn Studebaker's telephone has been ringing off the hook in recent weeks. Most of the calls to the University of Arkansas entomologist have been about an infestation of corn leaf aphids on newly emerged corn.
“This is the first time in a long time we've seen such high numbers of corn leaf aphids in early corn. They have been prevalent across the whole Delta of eastern Arkansas. We've seen huge numbers in some fields,” said Studebaker, who is with the Cooperative Extension Service. He's stationed at the Northeast Research and Extension Center in Mississippi County.
“I've looked at some fields that have newly emerged corn, and they don't seem to have the aphid problem. It seems to be the earlier-planted crop that had the problem. The aphids were mostly in no-till fields that had a lot of grass, and I'm thinking they moved off the grass after farmers applied herbicides and the grass began dying.”
Jeremy Ross, coordinator of Extension's corn verification program, estimated the size of the Arkansas corn crop at 350,000 to 400,000 acres.
“A few weeks ago,” he said, “the corn was only 1 to 1.5 inches, and aphids were covering the plants in some areas of the state.”
Studebaker said the problem looked much worse than it was. Corn leaf aphids aren't known to cause too many problems in corn even in high numbers. As a result, no threshold level has been established for treating corn leaf aphids in early corn, he said.
“I've been telling farmers not to treat if the plants aren't losing leaves or plants aren't dying from heavy aphid populations.”
He said a few weeks ago, early-planted corn wasn't growing well and the plants were yellowish. Farmers were concerned that the crop was in danger from the huge number of aphids present. However, Studebaker believes cold night temperatures were stressing the crop causing the yellowing problem.
“I didn't see any fields I would recommend spraying. The farmers I got to hold off spraying were happy the next week when it turned warmer and the corn began taking off and growing.”
Ross said favorable rain and warmer temperatures will help the crop outgrow aphids.
Despite the lack of problems posed by corn leaf aphids, Studebaker noted that the insect isn't always innocuous. He said they feed on plants and can kill them if the plants are drought-stressed. The insect is also believed to help spread viruses.
Meanwhile, Ross said, corn farmers need to apply post-emergence herbicides to the crop within the next couple of weeks. He said it's especially important to make the applications because recent rains will spur weeds to sprout.
Also, over the next couple of weeks, farmers need to apply side-dress nitrogen when the crop has reached the five-leaf stage.
As soon as these operations have been completed, Ross said, farmers need to lay their irrigation tubing and make sure their wells are operational.
Lamar James is an Extension communications specialist with the University of Arkansas.