University of Illinois

No. 13/June 20, 1997

One More Caution

With the cool and wet growing conditions encountered across much of Illinois, the corn crop remains "tender" and is fairly susceptible to injury from herbicides drifted from postemergence applications in soybean fields. In particular, drift of Roundup Ultra and the postemergence grass herbicides used in soybeans are of particular concern due to the inherent sensitivity of corn to these products.

Any herbicide is subject to drift if applications are made when conditions favor off-target movement. Nearly all postemergence herbicides have label statements about not making applications during conditions that favor off-target movement. Symptoms that drift has occurred are more apparent with some herbicides than with others. Much has been made about label statements indicating that applications should not be made when winds are in excess of, for example, 5 miles per hour. In the reality of the "postemergence spray world," days with wind speeds less than 5 mph are almost the exception rather than the norm. However, with corn in a very sensitive condition, a "little" drift may cause a great deal of corn injury.

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