Foliar fungicides rarely are used to control leaf blight diseases of field corn. The cost of the fungicide plus application usually exceeds the profit from increased yield except under severe disease pressure when susceptible hybrids are grown. Foliar diseases can cause significant yield losses if infection occurs between two weeks before to three to four weeks after tasseling. The earlier the disease starts in the field the greater the yield loss. It is important to keep the upper leaves and husks of the plant as disease-free as possible during the grain filling growth stage. Large yield losses only occur when foliar diseases attack the leaves above the ear leaf before mid-dent growth stage. Sweet corn growers routinely use fungicides, and seed producers growing susceptible inbreds have shown large yield increases by controlling leaf diseases with fungicides.
Fungicides are registered for the control of northern corn leaf blight, southern corn leaf blight, northern leaf spot, common rust and gray leaf spot. Before spraying, consider the following factors: the developmental stage of the grain, the amount of disease in the field, the potential yield, the prevailing weather, and the market price of the grain. Spray applications should begin before the fungus attacks the ear leaf. Greatest yield responses occur when the plants become diseased before tasseling and the plants are protected with a fungicide through the first four weeks of grain fill. Generally, fungicides should be applied when diseases like gray leaf spot or northern leaf blight are detected on half the leaves below the ear leaf. Current fungicide recommendations for corn can be obtained at www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/glsfungicides.htm.
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