Leaf Spot (Bipolaris, Drechslera, Exserohilum spp.), Leaf spots on turfgrassleaf blades begin as small red to purplish ovals that later develop tan centers of dead tissue with darker borders. The fungi that cause leaf spots directly penetrate leaf sheaths and blades at random or enter through mowing wounds. After recent nitrogen fertilization, when there is abundant moisture on the leaf blades, numerous leaf spot infections per blade can occur. The leaf spots may then coalesce and cause extensive blighting. The fungus may even invade the crowns and roots, leaving the plants weakened and rotted. This severe stage is called "melting out." Large areas of dead or badly weakened turfgrassmay result. Leaf spot fungi may be active at a variety of temperatures. All are associated with frequent moisture on the leaf blades and high relative humidity.