Figure 3. Gray leaf spot is a disease associated with continuous corn, especially when reduced tillage is used. The elongate rectangular lesions, gray in color, are characteristic of this severe leaf blight disease.
Fungi cause the majority of leaf blights. Gray leaf spot (Figure 3), northern corn leaf blight (Figure 4), and anthracnose leaf blight (Figure 5) are currently the most common and yield-limiting leaf blights in Ohio. The source of spores for these fungal leaf blights is old corn residue within, or adjacent to, corn fields. Of the economically important diseases listed in Table 1, only Stewart’s bacterial wilt and leaf blight (Figure 6) is caused by a bacterium. The bacterium overwinters in the gut of the flea beetle, and in the spring the flea beetle carries the bacterium to the young corn plants. Severe outbreaks of this leaf blight occur following mild winters which the beetle vector survives in high numbers. Warm sunny days favor flea beetle activity and spread of the disease. Symptoms of bacterial leaf blight are similar to northern corn leaf blight (Figure 4).
 Figure 4. Northern corn leaf blight lesions are elongate, necrotic areas, somewhat spindle shaped, and usually with straight or smooth margins. |
 Figure 5. Anthracnose leaf blight is most devastating in fields continuously cropped to corn. Anthracnose lesions appear blotchy with dark tan centers and yellowish-orange borders. Lesions appear first near the leaf tip and at the mid-rib. |
 Figure 6. Stewart’s bacterial leaf blight can be found on leaf surfaces that have been damaged by feeding of the adult flea beetle. Lesions are usually elongate, necrotic areas with wavy margins initiated at beetle feeding spots. |
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