Therefore, if hybrid corn producers are just now noticing that rust is severe, it is probably too late for a fungicide to be effective. On the other hand, if rust was noticed earlier, before it became severe, and a fungicide was applied, a second fungicide application may be justified. It is important to do some careful calculations about costs and returns. Unfortunately, it is not possible to precisely relate disease severity to yield loss. The earlier rust develops, the greater the loss.
Severe rust tends to shrivel grain rather than reduce grain number.
Several fungicides are labeled for use against corn rust. Various mancozeb products can be applied after silking. The label for Tilt specifies that applications not be made after silking. If Tilt is applied to seed corn after silking, the applicator is required to have a copy of the special label in his or her possession at the time of application. If using any fungicide, the label should be consulted regarding rates, timing of application, total amount that can be applied during the season, and other important considerations.