Gray Leaf Spot

Gray leaf spot usually attacks St. Augustinegrass, but it can also attack centipede. It is a summer disease caused by a fungus and is common in long periods of hot, humid weather. Newly sprigged or rapidly growing grass is more susceptible than well-established grass. Too much nitrogen fertilizer can make the disease more severe.

The disease causes irregular gray, dirty-yellow, or ash-colored spots with brown, purple, or water-soaked borders on leaf blades. Spots may be covered with gray mold in warm, humid weather. Lesions may occur on stems, spikes, and leaves. A yellow halo or general chlorosis may occur around some spots.

The disease is usually noticed first in shaded damp areas. In heavy areas, the grass may have a burned appearance. Seldom will this disease kill an entire lawn.

Fungus spores are spread by the wind, rain, irrigation water, and animals.

Control: Avoid excessive nitrogen (water-soluble) fertilization in summer. Water in the day so foliage will not stay wet overnight. Fungicides recommended include thiophanate-methyl, trifloxystrobin, clorothalonil, and mancozeb.