Gray leaf spot is a common disease found in St. Augustinegrass caused by the fungus Pyricularia grisea, but it has also made its way to annual ryegrass, perennial ryegrass and tall fescue recently. When does Gray Leaf Spot occur? Gray leaf spot is a generally a summer disease. The entire plant may be affected. Gray leaf spot may be showing up due to prolonged leaf wetness, brought about by nighttime watering, frequent rainfall, high humidity or heavy dew plus rapid, lush growth courtesy of recent fertilizations. Epidemics of gray leaf spot have been observed in New York State in the Southern Tier and the Hudson River Valley. Gray leaf spot, caused by the fungus Cercospora zeae maydis is the most significant yield-limiting disease of corn worldwide [1].The disease was first reported in Illinois in 1924, and has increased in prevalence throughout corn growing regions since 1988. Leaves turn yellow, then brown, then drop. It is more likely to develop in regions which experience high humidity levels and temperatures of 26-32 C. What damage or effects will Gray Leaf Spot have? Gray leaf spot has already been found on corn this year in Pottawatomie and Harvey counties when the corn was only in the V7- V8 stage of development. Gray Leaf Spot on Corn. . Gray leaf spot of St. Augustinegrass is a disease caused by a fungus that is common during extended periods of hot, humid weather. We have the fungicides you need to prevent those issues.. Gray leaf spot (GLS), caused by the fungus Cercospora zeae-maydis, has been one of the most prevalent foliar fungal diseases of corn in the state of Ohio ever since it was first reported in parts of Pickaway, Ross, Pike and Scioto counties in 1978. . Newly sprigged, sodded, or rapidly growing grass is more susceptible than well-established grass. How to Prevent and Treat Gray Leaf Spot in Houston. Leaf infections can progress into the crown area, resulting in death of individual plants. Lawns with severe gray leaf spot have areas that seem to just fade or melt away. What does gray leaf spot look like? Brown to black specks appear first on older leaves, then newer growth. Spots develop a gray center surrounded by a yellow halo. ; Disease development is favored by warm temperatures, 80°F or 27 °C; and high humidity, relative humidity of 90% or higher for 12 hours or more. In Harvey . The center of the spot may fall out leaving holes. Gray leaf spot is caused by the fungus Cercospora zeae-maydis. Gray leaf spot (GLS) is a common fungal disease in the United States caused by the pathogen Cercospora zeae-maydis in corn. Update in September 2018 – Because of the cool and very wet weather pattern we’ve seen over the last few weeks, there’s been a tremendous increase in reports of Brown Patch and Gray Leaf Spot in our area. 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