For Those Who Still Need To Apply N

With insight from Dr. Hartzler and Dr. Sawyer, here is some info on a potential area of concern. We are seeing fields being planted before N and/or pre-emergence herbicides are applied. While UAN (urea-ammonium nitrate, aka 28-32% liquid nitrogen) 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. In fact, to quote our campus specialists- “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.” I can vouch for that, as some of my customers will recall from a few of our attempts to do this; if you aren’t real careful, things can go south in a hurry.

Very Important- Check herbicide labels for restrictions on use of UAN as a carrier.
I had a wide range of results when applying 80+ pounds of UAN with herbicides on emerged corn from spike to around V5. Some key observations-

• If the corn was growing well and had endured relatively little stress, it tended to bounce back from the severe leaf burn from UAN and herbicides if the weather remained favorable.

• Same scenario, but if the weather turned stressful (in particular cold and wet), we could see some stand loss and some yield loss at year end.

• If corn had struggled early in the season, the additional stress of foliar burn and trying to metabolize herbicides was sometimes too much- and we had significant stand loss and/or plant stunting. It was simply too risky to tank mix high rates of UAN and herbicides on corn under stress, we learned to seek other options.