What is Brown Patch?

large, circular brown patch on grass

If you’ve noticed brown, circular patches on your cool-season lawn, brown patch may be to blame. Brown patch fungus can be hard to manage, but with the correct diagnosis and proper treatment, you can successfully manage these outbreaks.

What is brown patch?

Brown patch is a fungal disease caused by a strain of Rhizoctonia solani, a fungus that lives in the soil and attacks the foliage (leaf blades) of cool-season lawns. To add some confusion to the mix, brown patch used to encompass the fungal disease that attacks warm-season lawns as well. That disease has recently been re-named “large patch” to distinguish the two.

How does brown patch develop?

Cool-season lawns thrive in cool weather and have two growth periods: one in spring and one in fall. In the warmer months between spring and fall, most cool-season lawns will go dormant, and this is when a particular strain of Rhizoctonia solani will strike. 

illustration showing growth timeline for cool-season grass

Ideal conditions for brown patch disease in cool-season lawns:

  • Nighttime temperatures over 70 degrees Fahrenheit, daytime temperatures over 90 degrees Fahrenheit
  • Humid weather 
  • Cloudy days
  • Shade
  • Poor airflow
  • Poorly drained soil
  • Soil pH below 6.0
  • Watering late (early morning hours are best)
  • Excessive nitrogen
  • Too little phosphorus and potassium

Signs you might have brown patch

Turfgrass diseases can be very hard to identify. Many of them look identical to the untrained eye. 

Key signs to look for:

  • Patches are imperfect circles that are brown, yellow, orange, or tan
  • The patches range from a few inches to several feet wide
  • For grass cut above 1 inch, grass blades will show tan lesions with brown borders
  • Home lawns (cut above 1 inch) may develop mycelium — a stringy, gray, growth (like stretched cotton or a spiderweb) on the leaves — when the grass is wet with dew or other moisture
  • On grass cut below 1 inch, you may see a “smoke ring” — a dark ring around each patch

Types of grass that carry brown patch:

  • Fescues
  • Bluegrasses
  • Ryegrasses
  • Bentgrass

Word to the wise: If you’re an average homeowner (no offense intended), most lawn diseases look the same. If you’re unsure, take a grass sample to your local Cooperative Extension Office to get help making an accurate diagnosis. 

How to get rid of brown patch

Brown patch lives in the soil, and there’s nothing you can do about that. There are a few good ways to combat this fungus, however.

Natural solutions: Products with the active ingredient bacillus amyloliquefaciens strain D747 are often marketed as effective against brown patch. These products are usually OMRI certified, meaning organic producers can use this product. You can find brands that sell this product at local home improvement stores or online. 

Chemical solutions: If you notice brown patch in the lawn in the summer, you can take a curative approach and apply fungicides then. However, since the lawn grows very slowly or goes dormant during the summer, you may not see the effect until the lawn starts to grow again in the fall. 

Even if the grass returns to normal in the fall, the grass will likely show signs of the fungus again next spring. So, plan to take a preventive approach then. Start your rounds of fungicide applications in late spring when evening temps are consistently above 60 degrees Fahrenheit

If you’re planning to use chemical controls, you can choose from liquid or granular fungicides. Make sure the label says that it is OK to use on your grass type and that it controls brown patch. Some fungicides will have temperature restrictions as well (can’t apply over 85 degrees, for example), so read the label before you buy.

Cultural solutions: 

  • Wait until the lawn is dry before you mow
  • Mow the healthy lawn areas first; mow the diseased lawn areas at the end 
  • Collect the clippings if the weather is humid
  • Hose off the mower blade after you mow

How to prevent brown patch

One of the best ways to prevent brown patch is to plant a variety of grass species in your lawn. Cool-season grasses are often sold in a mix with different species of grass. Other times, you can buy a blend, meaning it contains just one species (tall fescue, for example) but two or more cultivars of that species. 

Do your research before you buy more grass seed. Ask your local seed supplier if any of the cultivars are better at resisting fungus than others. Tall fescue is particularly vulnerable, especially in the Southeast, so you may want to consider adding a mix of other species in your lawn to strengthen the stand of grass.

For other ways to reduce the risk or spread of this fungus, do what you can to prevent the ideal conditions listed above. You can’t change the weather conditions, like high humidity, but there are other things you can control. 

Have compacted soil? Aerate in the fall to provide better drainage and air circulation in the soil. (Aeration pulls plugs from the lawn to reduce compaction.) Want to fertilize the lawn? Get a soil test first to avoid using too much nitrogen fertilizer or failing to add enough phosphorus and potassium. These are simple ways to support your cool-season lawn when fungus attacks.


1. What else can I do to correct brown patch?

Here are a few other pointers:

If you have excessive shade, try to let in more sun or choose a grass alternative for that space. For example, pruning trees and bushes may let in more light. If those aren’t options or you don’t want to deal with the hassle, there are plenty of lawn alternatives to try.
In areas with less sunlight, try cool-season grass varieties that do well in partial shade: Strong creeping red fescue, chewing fescue, hard fescue.

2. Do these mowing tips make a difference?

Yes, according to the experts at North Carolina State University. They suggest that proper mowing and irrigation are key to keeping this disease in check. Here, again, are a few important points: 

Don’t mow when the grass is wet
Remove no more than one-third of the grass blade per mow
Have a sharp mower blade to cut instead of tear the blade (Diseases are less prone to enter a blade of grass if it has been cut cleanly instead of ripped or torn by a dull blade.)

3. Should I really water in the dark?

North Carolina State University recommends turning on the sprinklers just before sunrise and only watering as needed. These two things will prevent water from sitting on the grass blades too long and encouraging brown patch to develop.

When the grass growing gets tough, sometimes you need an expert in your corner. Contact one of our lawn care pros today to help you ID and treat the challenging spots in your lawn. 

Main Photo Credit: Scot Nelson | Flickr | public domain

Sarah Bahr

Sarah is a writer who has previously worked in the lawn care industry. In her spare time, she likes to garden, raise chickens, and mow the grass with her battery-powered lawn mower.