By Bruce SchultzBecause corn weed control starts with clean fields, LSU AgCenter weed scientist Daniel Stephenson is advising Louisiana corn farmers to take a proactive approach to controlling weeds.
First, a burndown of weeds should be done four to six weeks before planting. The end result removes weeds that will compete with corn for moisture and nutrition and eliminate habitat for damaging insects such as cutworms, Stephenson said. “It’s just imperative that a corn grower starts clean.”
A pre-emerge herbicide is essential to prevent new weed growth, and it should be mixed with atrazine to give a full spectrum of grass and broadleaf control, he said. “It is still the bedrock we need to plant our corn weed control program on.”
Stephenson said choosing a corn hybrid with Roundup Ready and LibertyLink traits will allow the producer to use glyphosate and Liberty for managing glyphosateresistant johnsongrass.
But, he said, it is imperative that farmers avoid using an organophosphate insecticide, such as Counter, during planting because those chemicals interfere with a plant’s ability to metabolize herbicides, such as Corvus, Capreno, Realm Q, Accent Q and other ALS-inhibiting herbicides.
Many farmers assume that a herbicide will have three months of residual activity, but such long-lasting chemicals were taken off the market long ago, Stephenson said. “Don’t expect any herbicide to give you three months of weed control.”
Most farmers only spray their crop when it gets about 12 inches tall, with no follow-up, but he said a second application is becoming more commonplace.
Eliminate Vegetation After Harvest
Because corn is harvested in Louisiana in July and August, weeds in harvested fields have several months to thrive, Stephenson said. Farmers who don’t control these weeds are recharging the weed seed bank. This means the fight against weeds will be even more difficult in the next growing season.
Using a residual herbicide, such as Valor, mixed with a non-selective herbicide, like paraquat, or making multiple tillage passes to destroy weed vegetation, is a good way to suppress seed production until cold weather arrives, Stephenson said.
Bruce Schultz is Assistant Communications Specialist with the LSU AgCenter.