Brown spots can occur in lawn grass despite a gardener's best efforts. These spots in an otherwise lush, green lawn look unsightly and stand out in the landscape. Although immediate treatment is necessary so your grass is green and even again, identifying the cause is essential in order to prevent the spots from occurring again. Dog urine, heavy foot traffic, fungal diseases, overwatering, overfertilizing and buildup of thatch are among several reasons responsible for grass brown spots.
Douse with water a brown spot that occurs soon after a fertilizer application. Excessive amounts of nitrogen cause grass to burn, resulting in brown spots. Water it immediately to dilute the effect and always follow label directions for appropriate application rates.
Apply a fungicide containing sulfur, chlorothalonil or benomly on round, brown patches that are 4 to 10 feet wide and have yellow edges and green grass growing inside. Such patches are caused by a fungal disease known as brown patch disease or summer patch. Follow label directions for applying the fungicide and repeat application every five days until the problem disappears.
Aerate compacted soil under a brown spot with a core aerator, to allow moisture to penetrate and reach grass roots. Compacted soils resist moisture penetration and are thirsty, which is why they cause lawn grass over them to form a brown spot. A core aerator does not punch holes in the ground, but pulls core plugs out, thus allowing moisture penetration.
Remove buildup of thatch with a thatch rake to allow water and nutrients to penetrate the soil. Grass clippings, accumulated leaves and plant debris prevent water, air and nutrients from reaching the ends of leaf blades and soil, thus causing the grass at that spot to turn brown. Once removed, nutrients and moisture easily penetrate the soil and reach grass roots, thus turning green again.