Pythium blight makes it easy to pull dead grass from the soil. Photo courtesy Cornell University
Environmental factors the last two months have been perfect for pythium blight, which seemingly overnight creates splotches of brown, dead grass. The heat and humidity mixed with the rain causes this fungus to show up usually in low-lying areas, shallow depressions or swales in the lawn.
“This disease is most common during hot, very humid weather. The disease can spread rapidly, killing large areas of seedling or established turf in as little as a day during conditions of high temperatures, high soil moisture and little air movement over the turf,” say Cornell University turf experts.
If conditions are right and nothing is done to curb the disease, large patches of lawn will be killed. It is particularly bad on perennial rye, but if severe, can infect bluegrass and fescues, too, although these are generally more resistant, Purdue University turf experts say.
The pythium fungus winters over in the soil and, when environmental factors align, is activated by water movement, which is why low-lying areas are most affected.
For the homeowner, the use of fungicides is considered a last resort, and only if the disease has shown up two years in a row. Purdue recommends contacting a lawn service for the fungicide treatment, which may require a license to apply.
Instead, turf experts recommend cultural controls: improving drainage in low lying areas, removing the lower limbs of trees to increase air circulation and delaying mowing until the grass is dry. Avoid high nitrogen fertilizers and watering the lawn in late afternoon or evening. Pull up the dead lawn and reseed or over seed with Kentucky bluegrass.
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I’ve seen this in my neighborhood and have some in my front lawn, as well. I am planning to have someone aerate the lawn this fall and then I’ll overseed it where needed.