Other mid-season leaf diseases also will be appearing soon, or have already been observed. Symptoms of common rust and eyespot are being seen already. Symptoms of gray leaf spot usually appear around the middle of July, usually as yellow flecks that turn into small, angular, tan spots. The long, rectangular shape does not develop until later. Generally, there is no immediate treatment recommended for these diseases in field corn.
Management includes use of partially resistant hybrids, crop rotation, and tillage.
However, it may be profitable in some hybrid fields to control gray leaf spot with a fungicide. Tilt is the only product specifically labeled for gray leaf spot. It is feasible to obtain a yield response in this range or greater when treating gray leaf spot with a fungicide. The trick is predicting which fields will have enough disease to benefit from a Tilt application. A single application at tasseling is probably most cost-efficient.