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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Rings Around the Lawn

This article was published originally on 9/15/1995
If your lawn is brown, you have lots of company. The summer of 1995 has been tough on turfgrass. Cool, wet spring weather slowed the growth of grass roots. Searing heat during parts of late June and July set the stage for a relentlessly hot, dry August and stressed-out turf.

Many browned-out lawns are just doing what comes naturally. Kentucky bluegrass, our dominant lawn grass species, is happiest in cool to mild temperatures with abundant moisture, so it grows and looks best in spring and fall. In the summer of '95, Kentucky bluegrass lawns that don't receive regular watering have gone dormant. They're not sick, just biding their time until cooler, moister weather allows them to green up and start growing again.

But some brown lawns have more complicated problems. A disease called summer patch has been unusually common and severe in Iowa and nearby states this summer.

Does your lawn suffer from summer patch? Describe your lawn problem in the following summer patch mini-quiz:

  • Do you see rings of straw-colored grass, up to a foot or more across, with green grass in the center of the ring?
  • Are the rings most common in sunny and hot areas (such as south-facing slopes)?
  • Did the problem start during July or August?
If you answered "yes" to these questions, summer patch is probably the culprit.
Summer patch is caused by a fungus that lives in the soil and attacks the roots. It nibbles on the roots during spring and fall, too, but shows its ugly self only in summer, when the lawn is stressed by heat and demands lots of water.

Summer patch damage ranges from slight to spectacular. A few rings may fade out in September, only to reappear during hot weather next summer. But under favorable conditions, hundreds of straw-colored rings can mass together, leaving only scattered tufts of green grass. This sort of wipeout usually requires overseeding or resodding to restore the lawn.

Summer patch thrives on stressed turf. So how do you avoid stressing your lawn in the summer? Here are some 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 by helping the roots breathe. You can rent or buy a core-aerator, or have the job done by a lawn care professional.

  2. Water thoroughly once per week during hot, dry summer periods. This usually works better than light, frequent waterings, which can encourage other disease problems. To relieve heat stress, some summer patch researchers recommend watering summer patch-prone areas for 10 to 15 minutes per hour during the hottest hours of the day (noon to 4 pm, for example).

  3. Mow high in summer. Set your mower for 3 inches or higher in July and August to conserve scarce water in the plants.

  4. 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.

A cost-effective defense against summer patch is to take advantage of genetic resistance. Overseed damaged areas with turf- type tall fescues, perennial ryegrass, and/or resistant varietiesof Kentucky bluegrass. Mixtures of resistant varieties or blends of different species tend to give the best results.

Systemic fungicides have been used to suppress summer patch. The catch is that applications must be made at monthly intervals in early May and early June, before summer patch symptoms appear. Fungicides are an expensive option for home lawns, and their effectiveness can be erratic, especially when the nonchemical management tips listed above are ignored. Lawns that are shielded from severe summer stress and armed with resistant genes will dodge the summer patch bullet.



This article originally appeared in the September 15, 1995 issue, p. 134.

Year of Publication: 
1995
Issue: 
IC-470(23) -- September 15, 1995