Some browning of a lawn is normal, especially when the lawn is entering seasonal dormancy or if there has been temporary damage, such as fertilizer burn. If you have browning grass without any obvious reason, though, you may be dealing with a fungal disease known as brown patch.

Symptoms

Brown patch doesn't begin with browning grass blades. Instead, you will get small areas in the lawn that look overly wet and matted down. This is when the fungus is taking hold. It will grow outward from the wet, matted-down center and kill the grass, causing it to brown. These brown, dead areas can grow quite quickly; there could be large spots within a few days. 

The initial brown patches will be roughly circular in shape, but they can vary in size or overlap so that the shapes are more irregular. Generally, the interior of the patch will be completely brown, while the margins may be yellowish or orange. The yellow-orange margins are where the fungus is active, while the brown section is the part of the grass that has already been destroyed by the fungus. 

Causes

The fungus that causes brown patch needs cooler temperatures and damp conditions to grow. It's often a problem in the fall or early spring months in areas with mild climates where warm-season grasses thrive, but it can occur more sporadically almost anywhere. 

Too much nitrogen in the soil, usually as a result of over-fertilizing, can also contribute to the growth of brown patch fungus. This is because the nitrogen feeds the fungus as well as your lawn. When this is combined with wet grass, perhaps from over-watering, conditions can become perfect for this fungal disease. 

Prevention and Repair

A combination of fungal treatments, applied by your lawn service, and improved cultural care will repair the problem and prevent it from happening again. Usually your service will first treat active brown patch sites to kill any fungus. 

Next, your irrigation schedule must be adjusted to avoid over-watering. Your lawn service may also recommend a dethatching and aeration treatment, which will open up the soil so moisture soaks in instead of collecting on the grass blades. Finally, your fertilization amount and schedule may need to be adjusted so that nitrogen is only provided during active growing seasons so it feeds the grass and not the fungus. 

Contact a lawn care service if you need more help with keeping your grass healthy.