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Learn Your Lawn: Summer Patch Disease

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Summer Patch is a disease that affects cool-season grasses, such as Kentucky Bluegrass, Tall Fescue, and Fine Fescue. As the name suggests, it typically occurs during the hot and humid summer months, particularly in areas with poor soil drainage or heavy thatch buildup. Symptoms include yellowing and browning grass with patches of dead or dying turf. These patches may be circular or irregular in shape and can range in size from a few inches to several feet in diameter.


Summer Patch is caused by a fungus called Magnaporthe poae, which attacks the roots and crown of the turfgrass plant. Damage from this disease will often occur where the grass receives direct sun and is located on south-facing slopes or near sidewalks, driveways, buildings, or otherwise stressed areas. In the cool weather of autumn, the grass may begin to grow into these dead areas again. 




Summer Patch is very difficult to control, as it thrives in hot and humid weather conditions. In most cases, the spread of the disease will be reduced by changes in weather, but you can also adjust some cultural practices to improve the health of the lawn and limit the spread. However, depending on the size of the infestation and the scope of the damage, other forms of control may be necessary and you may need to repair heavily damaged areas with sod or the appropriate grass seed. 


A thick, healthy, well-maintained lawn is the best line of defense. Here’s how you can adjust your beneficial cultural practices to reduce the spread of Summer Patch:

  • Avoid Watering: Under normal circumstances, you should be watering each area of your lawn for 30-45 minutes, twice per week, in the early morning so the turf is dry by nightfall. However, you should avoid watering when the disease is active, as it thrives with moisture.

  • Avoid Mowing: You should avoid mowing when the disease is active. If you do have to mow, make sure your mower blade is razor sharp, so that the blade does not fray the tips of the grass, spreading the disease. Maintain a regular mowing schedule throughout the growing season. In general, you should keep your lawn between 2 ½ and 3 ½ inches high, but during the hottest weeks of summer, you may allow the grass to grow as high as 4 inches. Never remove more than ⅓ of the grass blade at each mowing.

  • Fertilize Regularly: Regular applications of Weed Man’s specially formulated, slow-release granular fertilizer will help provide your lawn with adequate nutrients. These applications are timed specifically to avoid over fertilizing the lawn.

  • Core Aeration: Aerating your lawn can improve soil drainage and help reduce the likelihood of lawn diseases. This will also alleviate soil compaction and allow water and nutrients to penetrate deeper into the soil.


Your local Weed Man professional may be able to offer other solutions and recommend the best form of treatment that is available to improve the conditions of your lawn.