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Why Are Brown Spots in My Lawn: Fungal Diseases

August 12, 2021 | Categories: ,
Birdseye view of a patch of grass containing a brown spot in the shape of a question mark

There are a lot of things that can cause brown spots in your lawn, which makes it hard to get rid of the unsightly splotches. One of the more mysterious causes is fungal diseases. Three diseases all create brown patches in grass, but they each behave a little bit differently.

The first disease is brown patch. As its name suggests, this fungus shows itself in patches of brown grass ranging from four to twelve inches wide. Brown patch damages the grass blades themselves, which turn brown and form visible spots in your lawn. The spots have grayish-colored edges called smoke rings and can also have a white web-like layer called mycelium. Both of these symptoms are more visible on shorter mown lawns.

Brown patch
Brown Patch

Heat and humidity contribute to the development of brown patch. Your lawn may recover naturally from the disease as the weather cools, but you can also minimize the damage by watering and fertilizing it correctly.

Another patch disease that causes brown spots is called summer patch, which looks similar to brown patch. Summer patch also creates brown spots that can range from four to twelve inches wide, with the worst damage appearing at the edges of the patch. However, summer patch is a fungus that damages grass from the roots up rather than the blades down. You can recognize the disease by dark, rotting roots when you pull a handful of grass.

Summer patch
Summer Patch

The summer patch fungus infects roots in the spring, but the brown spots don’t appear until the heat of summer. In addition to good irrigation and fertilization practices, proper mowing height can help prevent the disease in your lawn. 

The third disease that can cause brown spots in your lawn is called dollar spot. Compared to brown patch and summer patch, dollar spot creates smaller spots that can range from two to six inches wide. These patches consist of damaged grass blades that have light brown spots on them. After a heavy dew, patches of dollar spot may also develop a layer of mycelium.

fungus in grass during cool season
Dollar Spot

Nitrogen deficiency contributes to the development of dollar spot, so proper fertilization is a good way to minimize damage. Again, good irrigation and mowing practices help protect your lawn from the disease as well. 

If you have brown spots in your lawn that look like the ones described above, then a fungal disease may be the issue. Otherwise, it could be one of a number of other problems causing the brown patches. Check back next week for another blog post addressing a different source of brown spots.