University of Illinois

No. 13/June 20, 1997

Controlling Waterhemp in Large Corn

The prolonged cool weather delayed the emergence of waterhemp in some corn fields across central Illinois; but, with the slow development of the crop, waterhemp has been able to come on strong. What can be done to control waterhemp in large corn?

Many postemergence products can be tank-mixed with atrazine, but cornheight restrictions (12 inches) may limit the use of this treatment. Additionally, late applications of atrazine may raise concerns about potential rotational crop injury.

Dicamba (Banvel or Clarity) can provide control or suppression of larger waterhemp. When used alone, broadcast applications may be made until the 5-leaf (8 inches) stage. After this, drop nozzles are needed to keep the herbicide out of the corn whorl. According to the label, a late postemergence application of up to 0.5 pint of Banvel (not Clarity) may be made to corn between 8 and 36 inches tall, or 15 days prior to tassel emergence, whichever comes first. Do not apply Banvel when soybeans are growing nearby if they are more than 10 inches tall or have begun to bloom.

Similar to atrazine, many postemergence herbicides use dicamba as a tank-mix partner. Use rates vary according to the label of the tank-mix herbicide, but generally do not exceed 8 fluid ounces of Banvel or Clarity. Applying these treatments with drop nozzles would be beneficial with respect to enhancing coverage of the target vegetation and reducing the potential for crop injury.

Some formulations of 2,4-D allow application with drop nozzles to larger corn and can provide control or suppression of waterhemp. Rates vary somewhat by formulation and drop nozzles should be used to apply 2,4-D when corn is larger than 8 inches.

Aaron Hager and Marshal McGlamery, Department of Crop Sciences, (217)333-4424