Summer patch, sometimes called Poa patch, occurs on Kentucky bluegrass and fine fescues on lawns and grounds, and on annual bluegrass on golf course greens and fairways.
Symptoms and signs
Symptoms of summer patch on lawns, grounds or golf course fairways appear identical to necrotic ring spot. Hence, diseased specimens may have to be examined by a qualified diagnostician if positive identification is necessary.
Symptoms of summer patch disease on Kentucky bluegrass lawn.
On putting greens, summer patch may begin as small (2- to 3-inch) circular patches that progress to larger (up to 12 inches) patches if conditions favor disease development. More often, large patches will appear suddenly with no indication of previous disease activity. In severe cases, the patches may coalesce and destroy large areas of turf. The patches initially take on a yellow color, then turn tan or a straw-brown color as the plants die. On greens with mixed annual bluegrass/bentgrass populations, the bentgrass usually will colonize the center of patches of affected annual bluegrass, creating a ring-shaped appearance.
Symptoms of summer patch disease on annual bluegrass
The causal fungus, Magnaporthe poae, colonizes grass roots in advance of disease causing activities. When conditions are favorable for disease activity, the fungus will invade the roots. Summer patch commonly occurs in midsummer during extended periods of high temperatures (> 82°F) following wet weather or heavy irrigation. The disease does not appear during the cool weather of spring and fall. Summer patch is more frequently observed in areas that receive heavy traffic, poor air circulation, and inadequate drainage.
Since summer patch is a root disease, cultural practices that promote good root growth will aid in reducing disease severity. Increased aeration and improved drainage on compacted and poorly drained soils will alleviate some root inhibition and enable the turf to better resist infection by Magnaporthe poae. Because low mowing heights are conducive to shallow rooting, raising the height of cut may result in less summer patch injury.
On golf courses, summer patch can be controlled with fungicides provided that applications are made on a preventative basis (3 to 4 weeks prior to symptom development) and high rates of penetrant fungicides are used. Application of fungicides with large amounts of water (5 to 10 gallons per 1,000 sq ft) has provided superior control in some locations. Chemical control of summer patch in lawns is generally considered too expensive.