Summer Patch on Turf

Lawns have been suffering this summer from a number of health problems. Other than the environmental problems (heat and moisture stress), one common culprit has been the summer patch fungus. Summer patch symptoms include circular patches of straw-colored grass, up to a foot or more across, often with green grass in the center of the patch. These patches are most common in sunny and hot areas (such as south-facing slopes). The browning typically starts during July or August.

Summer patch is caused by a fungus that lives in the soil and attacks the roots. It attacks roots during spring and fall, too, but symptoms are most often expressed in the summer months, when the lawn is stressed by heat and demands much water.

Summer patch damage ranges from slight to severe. A few patches may appear and fade out in September. These spots may reappear during hot weather the following summer. In other situations, hundreds of straw-colored patches may mass together, leaving only scattered tufts of green grass. When damage is severe, overseeding or resodding is usually necessary.

The summer patch fungus thrives on stressed turf. To avoid stress and subsequent disease problems, follow these suggestions:

  1. If your soil is high in clay, roots have a hard time getting enough oxygen for good growth. Aerating the lawn by removing plugs of soil during spring and/or fall can encourage growth.
  2. Aeration will also keep the thatch levels in check. Thatch is a sponge-like layer of organic matter and soil. When thatch layers become too thick, the turf is prone to desiccation injury, heat stress and disease. Thatch levels should be kept around one-half inch thick.
  3. Water thoroughly once per week during hot, dry summer periods if feasible. This usually works better than light, frequent waterings, which can encourage other disease problems.
  4. Mow high in the summer. Set your mower for 3 inches or higher in July and August to conserve water in the plants.
  5. Lush, rapidly growing grass is especially vulnerable to midsummer stress. If you fertilize your lawn, use split applications of a slow-release form of nitrogen (such as sulfur-coated urea) during spring and fall. Don't stimulate the lawn with nitrogen as the hottest months approach.
  6. Overseed damaged areas with turf-type tall fescues, perennial ryegrass, and/or resistant varieties of Kentucky bluegrass. Mixtures of resistant varieties or blends of different species tend to give the best results.
  7. Systemic fungicides have been used to suppress summer patch. Applications must be made at monthly intervals in early May and early June, before summer patch symptoms appear. Fungicides are an expensive option for homeowners, and their effectiveness can be erratic, especially when the nonchemical management tips are not implemented.

This article originally appeared in the August 23, 1996 issue, p. 149.


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