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.
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.