The most common ways to treat grass with brown patches are to avoid excessive watering, avoid walking over the brown patch areas and fertilize the lawn periodically. Since these brown patches are signs of fungal growth, these steps help inhibit fungal growth and strengthen the grass.
Typically brown patches occur after long periods of rain, as humid environments are ideal for fungal growth. In order to prevent brown patches, it is also important to rake leaves off the lawn. A thick layer of leaves prevents ground water from evaporating, thus increasing the chances of fungal growth. As a last resort, a homeowner may apply a fungicide to his lawn. These products are available at most home improvement stores.