Many types of fungi can infect soil; some cause harm to your lawn and garden plants, while others arise when there's an imbalance of resources in your garden but are quite harmless. Large outbreaks of mushrooms or discolored earth can detract from your yard's aesthetic value. Perform basic tests regularly to help you detect the presence of fungus so you know when to take action.
Scan your lawn and garden beds regularly to note any irregularities in the soil color. If you see discoloration on the soil, such as a crusty white film or yellow spores, there's likely fungus growing on your lawn.
Look for mushrooms, which are a large fungi. If you have a large crop of mushrooms that make a ring shape, your soil is likely infested with a fungus called fairy rings.
Note brown patches on your grass, which could be a sign of fungal disease. Drought or heat might cause your grass to turn brown, but if only part of your lawn discolors, you probably have fungus.
Watch your plants for signs of leaf discoloration, leaf curling, leaf drop or reduced vigor. When plants that were healthy display reduced or distorted growth, you've likely got soil fungus.
Contact your local county extension office if you encounter any of these problems. As of 2010, there were no reliable test kits for home growers, but county extension offices perform cheap and accurate soil testing. Arrange to have an extension officer take a soil sample and run tests to determine what type of fungus is in your soil.