Summer Patch

Ned Tisserat
Extension Specialist, Plant Pathology

Symptoms

Summer patch, sometimes referred to as frogeye patch, is a destructive disease of Kentucky bluegrass maintained for golf course fairways, parks and residential landscapes. The disease usually appears two to three years turf establishment from seed or sod and then reappears in subsequent years in the same location.

Summer patch symptoms in Kentucky bluegrass initially develop in June through August as small patches of turf, 2 to 6 inches in diameter. Grass blades in the patch change to a dull reddish-brown, then tan, and finally a light straw color. In the final stages of the disease, doughnut shaped patches of dead grass form throughout the lawn. Healthy grass may occur within patch centers resulting in a characteristic "frogeye" pattern. When weather conditions are ideal for disease development, affected areas may overlap and blight large areas of the lawn. Roots of affected plants are discolored, although this symptom may be difficult to see without the aid of a handlens.

Figure 1. Summer patch on Kentucky bluegrass lawn. Note frogeye appearance.

Figure 2. Extensive injury to bluegrass lawn from summer patch.

Symptoms of summer patch can be confused with insect damage (grubs, billbug), herbicide injury, or drought stress. These possible causes should be eliminated before a diagnosis of summer patch is made. The best means of confirming this disease is to submit a turf sample along with photographic images of the damage to a plant disease diagnostic lab for pathogen isolation. The turf sample should be cut from the margin of the patch that contains both healthy and diseased turf. Ideally, the sample should be 6 inches X 6 inches and deep enough to include much of the root system.

Summer patch also may cause extensive damage to annual bluegrass on golf course putting greens. Symptoms are similar to those described on Kentucky bluegrass, although blighting tends to be more non-uniform. Creeping bentgrass, which is not susceptible to summer patch, remains unaffected on the putting surface. This preferential damage of annual bluegrass is a useful diagnostic feature of the disease.

Figure 3. Summer patch on golf course putting surface.

Figure 4. Runner hyphae on roots of Kentucky bluegrass.

Conditions

The soil borne fungus (Magnaporthe poae) which causes summer patch colonizes grass roots and crowns in May and early June. It first grows on the root surface but later penetrates the tissue and invades the inner root tissue. Conditions in spring are optimal for turfgrass root growth, and even though fungal colonization is occurring, the turfgrass is able to absorb water and maintain growth. Therefore, foliar symptoms do not develop at this time. However, infected roots either die or become dysfunctional during the hot, dry summer months. Root growth is inhibited by high soil temperatures, and plants cannot rapidly replace diseased roots. Infected plants are no longer able to supply adequate water to the foliage and the plant dies. Circular patch symptoms develop because the fungus tends to grow radially out from a central infection point. The fungus can survive many years in the soil, and symptoms often develop yearly in the same location.

Control

Summer patch is a difficult disease to control but several cultural practices will help reduce disease severity. Turfgrass should be maintained in a vigorous, but not overstimulated, growing condition. A balanced fertilization program is important. Avoid excessive nitrogen fertilization during the summer months. Seventy-five percent of the nitrogen fertilizer should be applied in the fall. The use of acidifying nitrogen sources such as ammonium sulfate has been shown to reduce summer patch severity. Slow-release nitrogen fertilizers should be used for spring fertilization. Mowing heights should be maintained above 2 inches on residential lawns. Thatch reduction is important for suppressing disease development, and infested lawns should be dethatched yearly and/or core-aerated.

Summer patch may develop even with optimal turf care, and certain cultural modifications may be necessary to save the turf. Seriously diseased turf should be watered (syringed) daily in the early afternoon to cool the plants and provide some moisture for the diseased roots.

Certain Kentucky bluegrass cultivars have shown some tolerance to summer patch. For example, the older cultivars A-20, A-34, Adelphi, Admiral, America, Baron, Bristol, Challenge, Columbia, Eclipse, Majestic, and Monopoly have shown a moderate resistance to the disease. Unfortunately, many of the newer bluegrass varieties have not been extensively tested for resistance to this disease. The common type Kentucky bluegrasses, including Park, Kenblue, SouthDakota Certified, Ginger, Alene and Greenley are more susceptible to summer patch and should be avoided.

Several fungicides are labeled for the control of summer patch. Chemical control has not been completely effective in eradicating the disease, but it can reduce disease severity if used in conjunction with good turf management. Timing of fungicide applications is critical for effective control . Make the first preventive application in spring when the soil temperature at a depth of 2 inches remains above 65 degrees F. This varies with geographic location, but generally the first fungicide application should be made in early to mid-May, or about 2 to 3 weeks after the crabgrass germinates. A second application should be made one month after the first. The fungicides azoxystrobin (Heritage), propiconazole (Banner and others), triadimefon (Bayleton and others), and myclobutanil (Eagle) are recommended for the early season, preventive applications. Follow label directions concerning irrigation immediately following fungicide application.

Summer patch is more difficult to control with chemicals once symptoms have developed. The fungicide thiophanate methyl (Cleary's 3336, Fungo, and others) has been reported to be the most effective curative compound and can be used to suppress further disease development.

azoxystrobin

excellent

2 applications@ 28 days in spring

Heritage

fenarimol

fair

2 applications@ 28 days in spring

Rubigan

myclobutanil

good

2 applications@ 28 days in spring

Eagle

propiconazole

good

2 applications@ 28 days in spring

Banner

thiophanate-methyl

fair

variable

Cleary's 3336, Fungo, Cavalier, Systec 1998

triadimefon

good

2 applications@ 28 days in spring

Accost, Bayleton, Fungicide VII, others

trifloxystrobin

fair - good

2 applications @ 28 days in spring

Compass

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Web updated 9/01/06
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