Gray Leaf Spot

Pyricularia grisea

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  • Gray leaf spot, caused by the fungus Pyricularia grisea, is a disease that affects mainly annual and perennial ryegrasses and tall fescue; St. Augustinegrass and kikuyugrass are also susceptible. Areas with extended leaf wetness and high nitrogen concentration are more susceptible to severe outbreak and infection. Although it is common in the southern states, infections have been found as far north as Long Island, the lower Hudson Valley of New York State, and Pennsylvania. Infections and diseased tissue can appear quite quickly. Damage is usually noticed during the warmer months of late summer. If weather conditions are hot, humid and dry for extended periods, the damaged spots may grow up to 40 cm in diameter. The disease progresses so quickly that large areas of turf can be lost within a few days. The pathogen can produce large amounts of infectious spores in a very short period of time causing symptomatic tissue to become evident and decline very quickly. Spores land on a susceptible host and germinate within a few hours. The pathogen then invades the leaf tissue through the cut leaf tips. Symptoms can appear within hours of infection. Infected leaves may have water-soaked lesions and appear chlorotic. The youngest leaves often take on a characteristic fishhook shape. The disease is most severe on young seedlings. Damaged spots of turf first appear reddish-brown in color and 2 to 5 cm in diameter. A yellow margin may surround the damaged spot and the leaf blades may have dark brown borders.


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