Department of Crop and Soil Sciences - Cooperative Extension
Turfgrass Diseases
Summer patch, Magnaporthe poae
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 putting green.
Disease cycle
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.
Cultural control
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.
Chemical control
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 systemic fungicides are used. Application of fungicides with large amounts of water (5 to 10 gallons per 1000 sq ft) has provided superior control in some locations. Chemical control of summer patch in lawns is generally considered too expensive.
Take-all patch, Gaeumannomyces graminis
This disease has been called Ophiobolus patch or Gaeumannomyces patch. Only bentgrasses are susceptible, so it is seen most commonly on golf course greens and fairways, where it can cause serious turf losses.
Symptoms and signs
Take-all patch usually appears in the late spring or early summer as reddish-brown or yellow areas of dead grass. Infection centers appear as rings, crescents, or spots in pure bentgrass stands. The center of the patch often is invaded by annual bluegrass or other weeds. In mixed stands of turf, the bentgrass is killed and other grasses in the stand remain. Affected areas may enlarge as much as 6 inches or more in a year and eventually will exceed 3 feet. The symptoms become most conspicuous after turf has been stressed from hot, dry weather, even though moist, cool conditions favor infection and growth of the causal fungus.
Symptom of take-all patch on creeping bentgrass fairway.
Dead or dying roots may be covered with dark brown strands of fungus (runner hyphae), and dark brown to black mats of fungal growth may be present on the stem bases beneath the leaf sheaths and on the crowns and roots of the killed tillers.
Disease cycle
Take-all patch is most frequently observed on bentgrass planted in recently fumigated soils and/or in recently cleared forested or wetland areas. In these situations, the beneficial microorganisms that compete with or antagonize Gaeumannomyces are present in low populations. In most cases, the disease will decline over a period of 4 or 5 years, a phenomenon thought to be associated with the build-up of antagonistic microorganisms. The causal fungus grows on the surface of bentgrass roots and attacks the roots in cool, wet weather, although the symptoms do not appear until warm, sunny weather occurs.
Cultural control
Since disease damage is, time-wise, removed from the symptoms, it is important to implement control measures prior to symptom development. Bentgrass take-all is most serious in soils with pH above 6.0. In some cases, liming appears to stimulate the fungus. At present, the only effective control known for bentgrass take-all patch is the use of some form of sulfur or an acidifying fertilizer such as ammonium sulfate or ammonium chloride. Ammonium sulfate should be applied and watered-in two to four times yearly, in spring and fall.
Chemical control
Some of the broad-spectrum systemic fungicides may control this disease if applications are timed to prevent fungal invasion of bentgrass plants in cool, wet environments. However, results obtained from fungicide applications are erratic and rarely give complete control.