Fungus appears in grass as discolored areas of varying shapes and sizes, with some fungi covering the grass blades with powdery, threadlike or greasy coatings, states Today's Homeowner with Danny Lipford. Grass in areas affected by a fungus is usually thinner than grass in healthy areas of the lawn.

Soil tests can correctly identify the specific type of fungus, claims Today's Homeowner with Danny Lipford. Providing proper conditions for the healthy grass that remains successfully eradicates most fungi. Most types of grass require 1 inch of water per week for proper growth. Aerating the soil and removing thicker areas of thatch increases airflow and improves grass health. Disinfecting lawn mower blades before cutting the grass can prevent transmission of the fungus throughout the lawn; maintaining a taller grass height has the same effect. Fungicides are available to target specific types of fungi, killing the spores and protecting the lawn from further harm.

Grass fungus may resemble other common lawn problems, reports the University of California's Integrated Pest Management Program. Environmental stresses, such as improper watering, mowing and fertilizing, are often responsible for discolored areas of grass. High or low temperatures, chemicals and insects can also create discolor patches of grass.