How to Treat Brown Patch Fungus in Your Lawn

Fungal infections can cause brown, dead patches on your lawn. Brown patch fungus is caused by Rhizoctonia solani. The fungus often appears in mid to late summer in hot and humid weather. Brown patch is a foliar disease, meaning it harms the blades of grass but not the plant’s crown or root system.1

Rhizoctonia can affect any cool-season lawn grass but is especially harmful to ryegrass and tall fescue. Kentucky bluegrass and fine fescues can occasionally be affected, but the damage is usually minimal. Brown patch fungus can affect warm-season grasses, including St. Augustine grass and zoysiagrass.

Causes of Brown Patches in Lawns

• • Brown patch fungus: The main factors causing this fungus are excessive nitrogen and irrigation, lack of air movement, poor soil drainage, excessive thatch, and compacted soils. It can strike lush, green lawns and poorly maintained lawns. Sometimes, improving environmental problems, such as increasing air circulation, may be enough to eradicate a fungal issue. For persistent problems, you might need to move on to a fungicide and reseed with fungal-resistant varieties of grasses.
  • Grubs: Grubs eat grass roots, leading to small brown patches that widen into more prominent spots. Walking over grass patches affected by grubs feels sponge-like and is easily raked up because the roots are damaged. Treat the grubs with insecticide in the spring and reseed the grass in the fall.
  • Excessive thatch: Grass not adequately watered, fed, or mowed can accumulate dead and decaying plant material between the plant leaf blades and the root system. Sometimes, grass tries to grow roots in the thatch, but since it can’t hold water, the plants dry out and cause brown spots. Dethatch and aerate the lawn to fix this problem.

• Pet urine: Dog urine burns are caused by its high amount of nitrogen. It appears like brown centers and dark green outer rings. Water deeply to wash away the salts in the urine, aerate the spot to encourage new grass to grow, reseed the spot, or use a dog urine lawn treatment product.
• Foot traffic and leaving objects on the grass: A lot of foot traffic, like playing football or soccer or leaving a baby pool out for more than a few hours, can be enough to kill grass and leave brown patches over the lawn. Remove objects each day from the lawn. Also, consider playing on the lawn in different spots or lessening the frequency so grass can recover from foot traffic damage.

Common Seasons for Brown Patch Fungus

Grass fungus usually does not go away on its own. It’s also easy to spread fungus via foot traffic and grass clippings, so immediate treatment is important. Begin brown patch control in the spring with aeration and dethatching. Apply fungicide when the fungal patches appear (usually mid to late summer). Reseed with different grass species by over-seeding over several fall seasons. For quicker results, eliminate the old turf grasses in spring and reseed them immediately.

The Rhizoctonia fungus may be present in the soil for some time before it manifests as brown patch disease. The fungus overwinters in the lawn grass or soil beneath in the form of fungal bodies known as sclerotia, and it can survive for years until conditions are right.

Rhizoctonia is most likely to cause brown patches during periods of high temperature and high humidity in mid to late summer when night-time temperatures remain above 68 degrees Fahrenheit and daytime temperatures are routinely in the 80s or above. Periods of rainy weather when the air is saturated with moisture may also prompt the disease to emerge.