White Fungus on the Top Part of a Grass Blade

Powdery Mildew

• Probably the most common cause of a white fungal growth over the top of lawn grass is the disease known as powdery mildew. The fungus Erysiphe graminis infects the roots of grass plants. Along with the titular white powdery mildew, you may also notice the most shady areas of the grass turning yellow and dying. Powdery mildew is most common on bluegrass and other shade-tolerant grass varieties, and outbreaks are more likely to occur in temperatures of 60 to 72 degrees Fahrenheit.

Fusarium Patch

• Another common fungal disease of grass blades is fusarium patch, caused by the fungus Microdochium nivalis. This disease is commonly seen after a snow melt, and though visible fungal growth first appears yellow and bleached, if the grass remains wet, white cottony patches of mold break out over the tops of the grass blades. Fusarium patch develops on thatches of grass underneath snow, so fall lawn mowing and keeping the yard clear of grass debris are the best preventive control methods for this disease.

Pythium Blight

• The Pythium spp. fungi cause the disease pythium blight. Before any white cottony fungus is noticed on grass, the lawn will break out into dark-colored spots on grass blades. The spots eventually turn a tan color and may eventually kill the grass outright before white cottony mold breaks out over the grass. Excess watering late in the day is a leading contributor to infection from this fungus, so a well-timed irrigation schedule is the key to preventing this disease.

Slime Molds

• Many people know slime molds for their odd, offensive appearance that earns slime molds the nickname of "dog vomit fungus." The earliest signs of a slime mold growing on your lawn is a creamy white slime over the top of grass blades that later turns to a powdery texture and takes on a white, gray or blue-gray color. Slime molds very rarely cause problems for lawn grass, but the easiest methods for removing them is to simply rake or mow them up.