WOOSTER, Ohio - The presence of corn leaf diseases throughout Ohio is adding additional stresses to drought-stressed plants and may predispose the crop to stalk quality problems.
Pat Lipps, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that growers should be identifying which fields are suffering from diseases and marking those fields for early harvest.
"The impact of leaf diseases is that they are going to cause more damage to the leaves which will limit carbohydrate development needed to fill grain," said Lipps. "The problem is leaf diseases are using those carbohydrates and the plants are sacrificing the stalks to shift carbohydrates to produce grain and with that shifting the stalks become more susceptible to stalk rot." Lipps said the fields that may suffer the most stalk quality problems are those with reasonable yield potentials, because larger ears have more kernels that require more carbohydrates. "Those plants will disintegrate more quickly because of the bigger ears and the drain on the stalks," he said.
Despite widespread drought conditions that are keeping the moisture-driven corn diseases at bay, Stewart's bacterial leaf blight, gray leaf spot and northern leaf blight are showing up in fields throughout the state.
Stewart's bacterial leaf blight is the most common leaf disease being found in Ohio at this point in time," said Lipps. "There were a lot of flea beetles that overwintered and through their feeding, they transmit the disease to the corn plants throughout the summer." To identify Stewart's bacterial leaf blight, growers should look for lesions on the leaves that begin as small pale green water-soaked areas associated with flea beetle feeding tracks. The lesions rapidly enlarge, and as the tissue dies, the diseased area turns brown. The advancing edge of the lesions has a wavy outline, characteristic of the disease.
Early morning foggy conditions, which become more common in September, provide moisture on leaf surfaces that can give rise to gray leaf spot and northern corn leaf blight.
Gray leaf spot lesions are typically tan and rectangular in shape. When diagnosing gray leaf spot, said Lipps, look at leaves where the lesions are well separated by green tissue and appear to be limited to between the leaf veins.
Northern leaf blight lesions are cigar shaped, a half-inch to over one-inch wide and six inches or more long. The lesions are tan, but frequently the spores of the fungus may make the center of the lesions appear pale olive green color.
"Gray leaf spot and northern leaf blight are more common this year than in previous years, and the presence of the diseases even in a drought, means that there is probably going to be a lot of fungi survive the winter on old corn stalks," said Lipps. "Growers growing corn after corn could run into problems next year if the weather is favorable for disease development." The presence of diseases in the face of drought conditions also means that growers have strayed from disease-resistant hybrids. "If we didn't have the drought that we are having, the diseases would be much more prevalent and severe," said Lipps. "It's important that growers plant resistant hybrids to avoid problems next year." Lipps said corn growers are facing widespread premature death of plants, the most severe condition of the crop he has ever seen. "A lot of fields are dying prematurely from the drought and various other factors, and the diseases are one of those factors," he said.