Blue Fungus on Grass

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Grass that exhibits blue fungal growth may have contracted a disease called slime mold. This disease infects cool- and warm-season grass types, according to the Alabama Cooperative Extension website. It is important for gardeners to notice the signs of slime mold and provide treatment. Future slime mold problems can be prevented with proper cultural practices.


Slime Mold

Slime mold occurs during hot humid weather. Long periods of rain during the early spring and summer months encourages slime mold growth. This lawn disease is caused by physarum, fuligo, and mucilago crustacea species, according to the Alabama Cooperative Extension website. These species engulf organic matter during evening fogs and morning dews. In the hot afternoon sun, the slime mold dries up and forms a crust over the lawn. The disease can also occur on mulches and trees.


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Gardeners may notice signs of slime mold that include irregularly shaped patches of lawn that have taken on a blue, black or gray appearance, according to North Dakota State University's website. On close examination, gardeners may see brightly colored fruiting bodies appear on the surface of the grass blades. Patches of lawn take on an oily or greasy appearance right before the slime mold dries into a crust. Severe cases of slime mold leave entire lawns covered in the disease.



Treat slime mold by hosing down the yard in the morning, as recommended by gardening writer Walter Reeves on his website. The disease causes lawns to take on an unsightly appearance; however, slime mold does not hurt grass. Avoid washing off the lawn in the late afternoon to try to treat slime mold. Wet grass blades combined with cool nighttime temperatures increases the risk of your lawn contracting another fungal disease. Even severe cases of slime mold, do not need to be treated with fungicides.



Prevent slime mold taking over your yard by reducing your thatch layer. Slime mold is more common on lawns that have a thick thatch layer or one that is more than 1/2 an inch thick. Check the thatch layer by cutting out a 2-inch wedge shaped piece out of your turf. Measure the brown spongy material between the grass and soil. Rent a dethatcher to push back and forth across the lawn. Rake up the dead debris.