The Summer Lawn Fungus That Makes Turfgrass Look Patchy

You've weeded, watered, mowed, and fertilized, but you're still dealing with unwanted brown spots in your lawn. While most lawns experience patchiness and discoloration from time to time, persistent brown or yellow patches that continue to spread can be a sign of a more serious issue. Summer patch, caused by a fungus called Magnaporthe poae, is a disease that attacks turfgrass at its crown and roots.

This disease typically affects cool-season grasses like Kentucky bluegrass and fine fescue. In the early stages, summer patch presents as wilted circles of grass, about 2 inches in diameter. As the disease progresses through the summer, these patches will turn to yellow rings or crescents and increase in size. In the final stages, the grass will die back from the tip. If you're not sure summer patch is causing your patchy lawn, you can pull up some affected grass to examine the roots. If the roots are short and black or brown, summer patch is likely. Luckily, summer patch is easy to treat and prevent. Knowing how to spot summer patch early and treat the disease is key to keeping your lawn green and lush.

Summer patch typically occurs during the hot, humid summer months. Since it thrives on moisture, heavy thatch buildup, poorly drained soils, and excessive watering create an ideal environment for summer patch to flourish. Watering your grass deeply but infrequently, as well as aerating and dethatching your lawn, can help prevent summer patch. Mowing too short can also cause stress to your grass, making it more susceptible to disease, so make sure you mow at the appropriate height for your grass type.

If your grass is already infected, you'll need to treat it as soon as possible. Regular application of penetrant fungicides, like azoxystrobin and propiconazole, is effective in treating summer patch in its active stages. Aerating and irrigating before applying the fungicide may help it reach the roots better, where it can more effectively treat the disease. These chemicals can be rotated and should always be applied according to the package's instructions. Along with chemical treatment, correcting soil compaction, reducing thatch, and adding a nitrogen fertilizer to your soil will help treat the disease. Any dead grass should be removed and the ground reseeded.