Gray Fungus on a Lawn in the Early Morning

Identification

• Slime mold is a fungal disorder likely to affect all cool season and warm season grasses. The disease is caused by an infection from the Physarum, Fuligo or Mucilago crustacea fungi. Symptoms are seen when the fungal organisms cover and feed on bacteria, protozoa or decaying organic matter present in the grass. The disease often occurs on low growing perennials in the landscape.

Symptoms

• The disease is characterized by the appearance of 4- to 8-inch, round to irregularly shaped, gray to black patches on the grass. The patches are composed of countless tiny, pinhead-sized fruiting structures of the fungi resting on grass blades. These fruiting bodies are released when the grass is disturbed. Newly appearing slime mold patches have a slimy look but gradually dry to a crustlike form over time. The fungus is most evident during early morning hours and tends to dry rapidly in the sunlight.

Favorable Conditions

• Slime mold is favored by high humidity and moisture in the grass and air. Extended periods of rain during late spring and early summer favor fungal development. Heavy evening fogs and morning dews encourage the spread of the fungi over pine barks and organic mulches as well. The presence of heavy thatch in lawns promotes fungal growth. Grass that is growing in poorly drained soil is more prone to symptoms.

Control

• The fungus is primarily an aesthetic disorder that does not damage or discolor the grass. Cultural control measures such as thatch reduction, aeration and improving drainage are often sufficient to contain symptoms. The use of fungicides is unnecessary. Once the fungus has formed a crust, mow or rake over the area to destroy fruiting bodies. Spray the slime mold patches with a detergent solution made by mixing 1 tbsp. liquid detergent with a gallon of water to interrupt the growth of the fungus.