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Grey leaf spot (Cercospora zeae maydis)

Grey leaf spot: biology

GLS infected corn residue left on soil surface from the fall crop overwinters as mycelium until spring. When conditions are favorable, conidia germinate and can become windborne for long distances infecting the host crop. During the growing season, secondary spread occurs by further release of conidia from initial lesions. Disease development is favored by minimum tillage, continuous corn and extended wet, hot-humid weather conditions. It has been shown that it may take as much as 72 hours of humidity above 95% for sporulation and secondary infection to occur.

Grey leaf spot: Damage description

Initial Grey Leaf Spot (GLS) lesions appear on the lower corn leaves as small, dark green water-soaked circular areas with chlorotic halos, eventually expanding into ovals. Where conditions are favorable, disease progression moves up the plant as secondary infections occur. Developing lesions appear as brownish-grey, long (up to 2"), narrow, rectangular lesions that are restricted by veins present on the leaves and may run together killing the entire leaf surface. Pre-mature death of leaves may predispose plants to stalk rot infection.

Grey leaf spot: Management

There are several management options in controlling Grey Leaf Spot in field and specialty corn. Management of this disease should be on an individual field basis. Know the disease risk for each field and use one or a combination of these recommendations to lessen yield loss. 1) Plant selected hybrids demonstrating adequate levels of GLS tolerance. 2) Fields in continuous corn, perform tillage operations which completely bury infected residue. 3) Crop rotation away from continuous corn. Remember that this disease organism can be spread by wind currrents over long distances (several miles). 4) Foliar fundicide application of Quilt at the earliest sign of disease development as a preventative fungicide with systemic and curative properties for the control of GLS. In growing environments where disease infection is significant and early, yields can be reduced by as much as 50%.

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