Foliar diseases can cause serious yield losses in seed corn production on a regular basis, but they can be controlled effectively. Each of the last three years, seed producers have had substantial problems with either common rust or gray leaf spot. Some pre-plant decisions can strongly influence the severity of gray leaf spot and other diseases that overwinter in corn residue. This time of year is also a good time to consider the possible use of fungicides.
The most important step in effective management of foliar diseases is recognizing the susceptibility of the seed parents to the major diseases (northern leaf blight, gray leaf spot, northern leaf spot, common rust, eyespot). With this knowledge, you can plan which fields will need special attention. In general, avoid planting seed corn where corn was grown the previous year, especially if a severe disease (other than rust) occurred. If you must do this, we advise planting male sterile inbreds. Male sterile seed parents will suffer less yield reduction, because they are not detasseled. The defoliation stress of detasseling exacerbates yield loss due to leaf diseases. If male steriles are not possible, plant the more resistant seed parents.
Even if you follow these recommendations, you may need to use a fungicide to control leaf diseases on many inbreds. Fungicides labeled for corn leaf diseases include Bravo, Dithane, Manzate, Penncozeb, TennCop, and Tilt. If you are considering fungicide use, be prepared to begin scouting at about stage V8. Also be sure equipment and services are readily available, because the timing of the spray is crucial. Be sure your employees are trained to handle and apply fungicides, and that you meet all the requirements of the Federal Worker Protection Standard.