ASK the Expert – What are the brown spots in my lawn?

As the weather warms up from spring to summer, you may notice your lawn struggling to stay green and even develop brown patches. It’s always a good idea to implement good cultural practices to keep your lawn healthy, such as an adequate watering schedule, regular mowing, and minimal heavy traffic. But what about severe and persistent brown patches that basic lawn care won’t help?

You may be wondering if there’s a problem with your soil, such as a pH imbalance or a nutrient deficiency. However, the likely culprit for distinct brown patches in your grass is actually a fungal infection. Fungal lawn diseases tend to form circular patches or rings in lawns of different sizes and shades of yellow or brown. They usually require chemical fungicide application for effective treatment. Here are some common diseases your lawn might experience with the names of the fungi that cause them:

Brown patch (Rhizoctonia solani). These patches can be several feet large.

Microdochium patch, also called fusarium patch (Microdochium nivale). These brown patches are usually less than 8 inches big, but patches can connect to cover larger areas. Often they are pinkish or reddish.

Dollar spot (Clarireedia jacksonii). These brown spots tend to be the smallest, the size of a silver dollar.

Necrotic ring spot (Ophiosphaerella korrae). These light green, yellow, or brown patches tend to have fairly healthy grass at the center.

Fairy rings (Maramius oreades and others). Fairy rings are famous for being circles of mushrooms that pop up in your yard, but some versions instead manifest as a large circle (or semicircle) of brown grass. They can be up to 15 feet across, or even larger in some cases.

Shown Above – Fairy Rings

When recovering from a fungal infection, removing, and disposing of grass clippings from the infected lawn can help prevent the disease from spreading. It’s also important to limit watering to what is necessary since fungi thrive in damp conditions. However, as with human disease, prevention is the best cure! Annual soil testing to determine the right fertilizer rate for your lawn—and adding neither too little nor too much—can keep your grass at its strongest and lower susceptibility to fungal diseases before they appear. Let’s also not forget that many soil fungi are beneficial for your lawn because they form symbiotic relationships with plant roots and assist with water and nutrient uptake. Regular lawn care and monitoring to catch diseases early can help reduce the need for fungicide applications and keep your lawn green and healthy.