What do you do when your beautiful cool-season lawn looks like it’s been taken over by a circular superbug? In this article, we’ll share the know-how you need to treat or prevent this common cool-season lawn disease.
What is brown patch?
What is brown patch? Brown patch is a fungal disease that attacks cool-season lawns during the warm season (late spring through early fall). Caused by a strain of Rhizoctonia solani, it will wreak havoc on a lawn if the conditions are right.
Don’t confuse brown patch with large patch. Large patch only affects warm-season grasses (bermuda, Zoysiagrass, St. Augustinegrass, etc.). The tricky thing is that 1) Both brown patch and large patch used to be identified under the name “brown patch” and 2) Both diseases come from the same fungus Rhizoctonia solani.
How to ID brown patch
Brown patch, like most lawn fungi, is very hard for homeowners to identify. If you want to try, here are common signs of this fungus.
Symptoms of brown patch:
- Circular patches on the lawn. Will be tan, brown, yellow, or orange.
- Patches are as small as a few inches or as large as a few feet wide.
- If your lawn is cut above 1 inch, you may see mycelium (looks like a spiderweb) on the leaves when wet (with dew, for example).
- On most home lawns (cut above 1 inch), you’ll see tan lesions on the grass blades. The lesions will have a brown ring around the edges.
- Low-cut grass (on golf courses) may develop a “smoke ring” (black ring) around the circular patches.
Grass types that host brown patch:
- Bentgrass
- Bluegrasses (Kentucky bluegrass, etc.)
- Fescues (tall fescue, fine fescue)
- Ryegrasses
If you want to be 100% sure of your diagnosis, contact an expert. Your local Cooperative Extension office is ready and willing to help. Take in a sample or send a photo to get an expert to ID the disease.
What causes brown patch?
Brown patch won’t damage the lawn until the climatic and grass conditions are favorable.
Conditions that lead to brown patch disease:
- Poor soil airflow and drainage
- Too much shade or cloud cover
- Soil pH is too low — below 6.0
- Too much nitrogen or too little phosphorus/potassium
- Humid weather
- Warm temperatures — daytime temperatures are above 90 degrees Fahrenheit and nighttime temperatures are above 70 degrees Fahrenheit
How to treat brown patch
Once the brown spots overtake your lawn, you want to know how to get rid of them pronto. Fungus in the lawn can be notoriously difficult to get rid of, but don’t give up the fight just yet. Here are a few tried and true ways to help your lawn recover from this unsightly disease.
Organic treatment: If you’re looking for a natural product to treat your lawn, look for products with the active ingredient bacillus amyloliquefaciens strain D747. Most of these products will be OMRI certified, meaning they can be used in organic production.
Chemical treatment: There are several commercially available fungicide treatments for brown patch. Plan to rotate between two or more chemicals to prevent your lawn from building a resistance to one chemical.
Fungicides come in liquid and granular options. Make sure the product works for your grass type and controls brown patch. (The label lists every fungus it will treat.) Sometimes these chemicals can’t be applied once temps get too high in the summer, so look for that on the label as well.
Lawn fungicides to treat brown patch:
- Azoxystrobin (alone or with Propiconazole)
- Pyraclostrobin with Triticonazole
- Fluoxastrobin
Brown patch fungi will develop resistance to azoxystrobin or fluoxastrobin if you use these products on their own. Use either of these in an alternating pattern or choose a product with at least two active ingredients to ensure the chemicals remain effective.
If this is the first summer you’ve noticed brown patch fungus in your lawn, feel free to apply fungicides at that time. Know that a curative approach may not produce results quickly since cool-season grasses grow more slowly in the summer. And once fall is near, the conditions for the fungus decline and the turfgrass usually returns to normal on its own.
Even if your lawn looks healthy again in the fall, know that you’ll likely have the same problem next year. Whether or not you choose to take a curative approach in the summer, you can take a preventative approach next spring. Once spring nighttime temps get above 60 degrees Fahrenheit consistently, start your first round of fungicide applications to prevent another outbreak.
Cultural treatments and prevention:
You can’t change the fungi that live in your soil, but you can keep your lawn healthy. This helps prevent unnecessary stress during those transitional seasons.
| Problem | DIY Solution |
| Soil pH is too low – below 6.0 | Follow your soil test’s recommendations for how much lime you’ll need to raise the pH |
| Poor soil airflow | Aeration — fall is ideal for cool-season lawns |
| Lawn stays wet for a long time | Change your watering schedule (before 8 a.m. works best) |
| Not enough phosphorus or potassium | Follow your soil test’s recommendations for how much to add to correct the problem |
| You only have one cultivar or species planted in the lawn. | Overseed the lawn with a different cultivar or a cool-season mix that includes different species of grass. This adds genetic diversity and helps reduce the risk that the entire lawn will be equally affected by the fungus. |
| Too much shade | Consider trimming back trees or planting a grass alternative in the area |
| Too much thatch – over ½ inch or more | Rent a dethatching machine |
| How not to spread the disease while mowing | Mow the lawn to the correct height for that species. Remove the clippings on humid days and don’t mow unless the lawn is dry. Mow healthy areas first, and save the diseased areas until the very end. Hose off your blades between mowings. |
Pro Tip: Don’t apply nitrogen fertilizer while the fungus is active in your lawn.
FAQ
If you want to make those brown spots go away pronto, paint the lawn. Yes, it’s a legitimate practice, and it’s quite popular in drought-stricken areas in the West. Think of it this way: It’s like makeup for your lawn. Grass paint helps your grass look good even when it’s fungus- or drought-stricken.
Preventive treatments for fungal diseases are fairly similar:
—Water early in the morning and water infrequently
—Cut at the correct height
—Only mow once the lawn is dry
—Don’t mow diseased areas (or mow them last)
—Optimize soil pH and nutrient levels
—Minimize shade
—Aerate if soil is compacted
If you’re using natural or chemical treatments, look at the label to see if the product will treat other types of fungi.
In addition to aerating the lawn, another helpful tip is to avoid heavy mowing equipment. Having heavy equipment on the lawn consistently will compact the soil over time.
If you’d rather have a professional manage this fungal disease, contact one of our local lawn care professionals. They have the experience and expertise to deal with common lawn fungal issues.
Main Photo Credit: Mr Thinktank | Flickr | CC BY 2.0
