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Gray Leaf Spot

August 21, 2009

Gray Leaf Spot Cercospora zeae-maydis is a fungal disease that affects corn. This disease was first found in PA in eastern Cumberland County in 1978. I found that interesting since I am now the Agronomy Extension Agent in Cumberland County and I am writing this blog from Cumberland County!! Gray Leaf Spot(GLS) is generally found in low-lying fields and areas that tend to stay wet. GLS loves long periods of overcast, warm, high humidity days. Corn growers that utilize reduced tillage and/or continuous corn have seen an increase in the occurance of GLS.

GLS symptoms start out as small yellow to tan lesions on the corn leaf. These lesion show up on the lower leaves first. The lesions will be up to 4inches long and 1/8 inch wide. The lesions form in between the leaf veins. This restricts the pathogen growth and lesion width. Around the two week mark the lesions will begin to look tan to brownish and be rectanglur in shape. Once conditions become favorable for the production of spores, the lesions will start to look silvery-gray. Crop yield reduction can range from 5 to 40 bushels per acre, depending on the timing and extent of the infection. There are no known problems associated with feeding GLS infected corn silage to livestock.

Gray Leaf Spot

GLS survives the winter in corn residue left on the soil surface. In late spring, if conditions are right, the fungus in the residue will produce spores that blow via wind on to the lower corn leaves. If infection occurs, the lesion on the lower leaves will produce spores that get blown upward onto higher corn leaves and the cycle continues until the whole plant is infected or conditions become unfavorable.

The best and most economically way to reduce GLS impacts on your corn crop is to plant GLS resistant varieties. These varieties will show symptoms of GLS later in the season, but the yield losses will be greatly reduced. The second best way is to rotate the infected field out of corn for two years. It is not recommended to rotate into wheat or sorghum. There are a few fungicides available on the market that manage GLS. But the economics of using a fungicide should be considered before an application is done. Contact your local Farm Supply Store or Fungicide Dealer for more information on what products to use and application.

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