One of the common problems we encounter in early summer on St. Augustine grass is a leaf spot disease called Gray Leaf Spot. Gray leaf spot develops rapidly with moisture and warm temperatures on St. Augustine grass, especially in shaded areas that are damp for long periods of time, or in low-lying spots, or where runoff flows. The disease can cause serious thinning of turf.

Leaf spots first appear as tiny brown to ash colored spots with purple to brown margins that grow and become oval or diamond shaped. Sections of the leaf blade will turn yellow. and in severe cases lesions develop on stems and spikes and the leaves wither and die. Turfgrass may have a burned or scorched appearance resulting from death or spotting of the leaf blades. Avoid applying a lot of soluble nitrogen fertilizers on shaded lawns during summer months. Water early in the morning, and only when needed. Avoid evening waterings that keep the surface wet for long periods. Remove grass clippings where gray leaf spot is a problem.

Several fungicides are recommended for gray leaf spot control, including azoxystrobin (Heritage), myclobutanil (Spectracide Immunox, Eagle), propiconazole (Fertilome Systemic Fungicide, Ortho Lawn Disease Control, Bannar Maxx), and thiophanate-methyl (Green Light Systemic Fungicide, Ferti-lome Halt Systemic Fungicide, Scotts Lawn Fungus Control, Bonide Bonomyl Turf and Ornamental).
 

Slime Mold

Another weather related turf phenomenon is slime mold. Slime mold often appears ashy or oily on grass. Closer examination reveals a granular, crusty, or powdery material moving up the grass from the thatch and soil surface.

The good news is that slime mold is not harmful to grass, but is still visible. Slime mold lives mostly unseen, breaking down and feeding on organic matter in the thatch and on the surface of the soil. When environmental conditions are right, it goes from a vegetative state to a reproductive mode. This is when the spore masses become visible. It moves up grass blades, and turns into a large mass of spores that are then blown in the wind and put in runoff water. The spores rub off on your shoes or hands when touched. Besides looking unsightly, slime mold does no harm, and can be washed or swept off the grass without fungicides.

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