Small Round Brown Spots in Winter Grass

Cool Weather Fungus

• Winter brown patch is a soil-borne fungus that can create damaged spots in cool-season grasses during the winter. Lawns that have a layer of thatch more than an inch thick are susceptible to this disease when temperatures fall below 50 degrees Fahrenheit. Winter brown patch thrives in low spots in the lawn with poor drainage and areas of heavy thatch. The main symptom of winter brown patch is irregularly shaped brown spots that begin as small discolorations measuring a few inches in diameter. Over time these spots grow in size and merge into each other. These spots can grow up to 3 feet in diameter, but it rarely causes serious damage.

Controlling Fungus

• The best way to control winter brown patch is through preventative care. Removing thatch during the spring and fall with a rake or dethatching tool removes the growing medium this disease thrives in and helps prevent its development. Heavy doses of fertilizer applied during the fall are another factor that can contribute to winter brown patch. Avoid using fast-acting fertilizers with a high nitrogen content during late fall. Areas of shaded lawn surrounded by large trees or landscaping with dense foliage can block air flow and create the dim, moist conditions where winter brown patch thrives. Thinning out thick foliage around problem spots in your lawn helps reduce the damp, shaded conditions that encourage fungi to form.

Wintery Damage

• Late in the winter, small brown spots can appear when the air is warm enough to allow grass to grow while the ground is still frozen in places. This causes previously dormant grass to begin using resources it cannot replenish from the frozen ground. This problem often occurs where there are isolated parts of the lawn in shade or in low areas where poor drainage causes excess water to collect and freeze. Leveling low spots in the lawn and removing the source of shade can alleviate winter freeze damage.

Chemical Damage

• De-icing salt spread on the lawn by careless handling or passing vehicles can cause brown spots to appear on your lawn. The only way to prevent salt from damaging your lawn is to keep it off the lawn. If you need to spread de-icing salt on a driveway or sidewalk, use as little as possible and avoid salting the edges of paved area where it meets the grass. Shoveling salt-laden snow onto the lawn to completely clear a walkway is a common source of salt damage. You can irrigate trouble spots with water once temperatures are above freezing to help reduce the amount of salt in the soil and alleviate the cause of salt-induced brown spots.