By Pete Landschoot, Ph.D.

Summer patch, sometimes called Poa patch, is a root and crown disease of golf course turf, home lawns, grounds, and athletic fields.

This hot-weather disease is caused by the fungus Magnaporthiopsis poae and occurs on annual bluegrass, Kentucky bluegrass, and fine fescues. Creeping bentgrass, perennial ryegrass, and tall fescue are highly resistant to summer patch.

Symptoms and Signs

On annual bluegrass putting greens, tees, and fairways, summer patch may begin as small (<4-inch diameter) circular patches that progress to larger (4 to 18-inch diameter) patches as the disease worsens. Large patches will often appear suddenly with no indication of previous disease activity. In severe cases, patches may coalesce and destroy large areas of turf. Summer patch-diseased annual bluegrass initially takes on a yellow color, then becomes brown as affected plants die. On greens, tees, and fairways with mixed annual bluegrass/creeping bentgrass populations, creeping bentgrass will often colonize the center of diseased patches of annual bluegrass.

Symptoms of summer patch in lawns, grounds, and athletic fields typically begin as circular areas of wilting Kentucky bluegrass or fine fescue turf, progressing to reddish-brown or light brown sunken patches, often with a tuft of healthy grass in patch centers. Patches range from a few inches to over three feet in diameter and can appear as a mix of rings, crescents, or spots of various sizes. In severe cases, patches of diseased turf can coalesce, making field diagnosis difficult.

Read the full article in the Spring 2025 issue of Pennsylvanina Turfgrass – https://theturfzone.com/ptc/?ascat=72&sub=issue&issue_id=9405&rti=true&rel=2