What Does Fungus on Grass Look Like?

Discoloration

• Most fungal diseases cause grass-blade discoloration. Gardeners are able to identify what type of fungal disease has infected their grass by the color of the blades. For example, necrotic ring spot causes red to straw-colored grass blades. Rhizoctonia yellow patch turns grass light green to yellow, while summer patch makes grass turn a bronze color. Oftentimes, diseased grass changes its discoloration, such as when grass infected with Rhizoctonia blight changes from purple to straw-colored when dried out in afternoon sun.

Spots

• Spots or lesions may be seen on diseased grass blades. Fungal diseases such as leaf spot causes grass to display purple to brown spots with light-colored margins on grass blades. When leaf spot is allowed to go untreated, spots on the blades merge together and the disease spreads down the leaf sheath to the root system. When the disease enters the root system, the entire plant dies out. Sclerotinia dollar spot is another disease that causes spotted grass blades.

Fungal Spores

• Certain fungal diseases produce fruiting bodies of fungal spores on grass blades. Rust causes orange-red pustules to form on grass. When gardeners walk on or mow the lawn, these pustules burst and rust-colored dust or fungal spores fill the air. Pink snow mold or Fusarium patch grows a cottony-pink fungal mat on top of grass blades. Gray snow mold, though, causes grass to develop hard, black fungal bodies.

Pattern

• Some fungal diseases discolor grass in a circular pattern. Rhizoctonia blight, Sclerotinia dollar spot and necrotic ring spot produce circular patches of discolored grass. Whereas, Fusarium blight infects grass in a crescent-shaped pattern. Fungus-like stripe smut does not create diseased patches of grass; instead, lawns exhibit patchy growth, uneven texture and thinning areas. When left untreated, the size of fungal disease generally expands over time.