When a brown patch appears, most homeowners assume the lawn needs water. Sometimes that is right — but often the culprit is a fungal disease that watering will only make worse.
Brown patch appears as circular patches of thin, brown grass up to several feet across, most common in hot, humid weather. It thrives on overwatered, over-fertilized lawns.
Dollar spot creates small, silver-dollar-sized sunken patches that can merge into larger areas. It is a sign of low nitrogen and is common on under-fertilized turf.
Snow mold shows up in early spring as pink or grayish circular patches in areas where leaves were left on the lawn over winter. Prevention is mostly a fall cleanup issue.
Fairy rings are dark green circles of faster-growing grass, sometimes with mushrooms. They are caused by organic matter decomposing underground and are mostly cosmetic, but can be managed.
The key with any disease is early diagnosis. If a patch is spreading despite watering, stop watering and call a professional. Fungicides work best as preventatives, not cures.