UAN and Herbicides on Emerged Corn

May 14, 2015
ICM News

By Bob Hartzler and John Sawyer, Department of Agronomy

Corn planting progressed so quickly in many parts of the state that herbicide applications couldn’t keep up with the planters. Corn may emerge before sprayers can get back in the field. While UAN (urea-ammonium nitrate) and many pre-emergence products can be applied to emerged corn, using UAN as a herbicide carrier enhances the foliar activity of products and may result in foliar damage. Check herbicide labels for restrictions on use of UAN as a carrier.

UAN alone can be applied to emerged corn, and the risk of injury to the corn is dependent upon UAN rate, corn stage and weather conditions. Conservative suggestions are to limit postemergence applications of UAN to 90 lb N/acre when corn is at the V3 to V4 stage and to 60 lb N/acre at the V7 stage. Applications beyond the V7 stage are not recommended, and the risk of injury increases during hot, dry conditions.

The combination of herbicides with UAN greatly enhances the foliar activity of these products and poses a real threat of killing all emerged tissue contacted by the spray.  

Some might try to rationalize this combination if the corn is at the VE-V1 stage since the growing point is still underground. While corn often can recover quickly from loss of the shoot at this growth stage, the herbicide may influence the plant's ability to recover and therefore result in uneven plant size and yield loss. 

 

Bob Hartzler is a professor of agronomy with extension, teaching and research responsibilities. He can be reached at hartzler@iastate.edu or 515-294-1923.

John Sawyer is professor with research and extension responsibilities in soil fertility and nutrient management. He can be contacted at jsawyer@iastate.edu or 515-294-7078.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 14, 2015. The information contained within may not be the most current and accurate depending on when it is accessed.

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