SUMMER PATCH DISEASE OF LAWN GRASSES

Agronomy Mimeo 81Revised February, 1995

INTRODUCTION

SYMPTOMS

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Symptoms of summer patch initially appear as wilted, dark-green, and roughly circular areas of turf that are 1 to 2" in diameter. The affected turf soon turns a straw-brown color, leaving patches that initially resemble the symptoms of dollar spot disease. These patches increase in size and may take on crescent shapes, elongated streaks, or circular patches. The outer periphery of patches may have a yellow or bronzed appearance, and leaves die back from the tip. Healthy turf may persist in the center of blighted patches producing rings or "frog-eye" symptoms. The most common symptoms are circular, straw-colored patches that range from 3 to 12 inches in diameter. There may be living plants in the center of patches, but distinct frog-eyes are not too common. Circular depressions, called "crater pits", are occasionally present. Affected regions may coalesce, and large areas of turf can be destroyed within a 7 to 21 day period. Creeping red fescue turf develops orange or bronze-colored patches prior to affected plants turning straw-colored. Crater pits are more common in creeping red fescue than Kentucky bluegrass.

Summer patch most commonly occurs in Kentucky bluegrass lawns that are 2 years of age or older. The disease seldom causes significant injury to Kentucky bluegrass younger than 2 years of age. The disease may appear in newly sodded lawns because sod is often 2 or more years of age before it is harvested. Summer patch, however, frequently appears in the summer following a fall seeding of creeping red fescue.

 

PREDISPOSING CONDITIONS

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Environmental conditions play a significant role in the predisposition of turf to summer patch. The disease is always more severe in full sun. Symptoms generally appear in late June or early July when day time temperatures above 90°F prevail. Soil temperatures above 78°F in the root zone and moist soils are critical factors in predisposition of turf to summer patch. The activity of the disease declines with the advent of cooler weather in mid-to-late September. Summer patch is most severe on sunny, exposed slopes or other very warm areas of a lawn such as those adjacent to walks and driveways. Conversely, it tends to be less severe in shaded sites. Drought stress following warm and wet periods, and compacted soil are other factors that enhance summer patch. Other predisposing factors include: spring applications of high levels of nitrogen fertilizer, accumulation of thatch, and frequent light irrigations or rain storms. Low mowing is the major cultural factor that contributes most to increasing disease severity. Scalping lawns by mowing very low after allowing the turf canopy to grow too high can trigger the disease.

CONTROL

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Chemical control of summer patch is difficult and expensive. The most cost effective method of fighting any plant disease is through planting of resistant species or cultivars and increasing mowing height. As noted previously, Kentucky bluegrass and creeping red fescue are most susceptible to summer patch. Other lawn grasses such as tall fescue and zoysiagrass are resistant and possibly immune to this disease. Many Kentucky bluegrass cultivars used in the past are known to be susceptible to summer patch, especially Merion', Baron, Windsor' and Fylking'. Cultivar evaluations conducted at the University of Maryland indicate that Aspen', Classic', Eclipse', Freedom', Georgetown', Kelly', Liberty', Lofts 1757', Monopoly', Suffolk' and Trenton' have good summer patch resistance. These Kentucky bluegrass cultivars, however, may become susceptible to the disease if mowed below 2.0 inches during summer. All cultivars of creeping red fescue appear to be susceptible to summer patch. Cultural and chemical approaches to summer patch control are as follows:

Cultural Approaches

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1. Avoid excessive nitrogen fertility, especially in the spring. Use an acidifying, slow release nitrogen source such as sulfur coated urea. Apply 75% or more of the total annual amount of nitrogen fertilizer per year during the autumn months.

2. Increase mowing height to 2.5 to 3 inches

3. Avoid light, frequent applications of water. Irrigate when turf shows initial signs of drought stress. Apply enough water to wet soil to a depth of 3.0 inches or deeper.

4. Reduce thatch when the layer exceeds inch thickness. (See Agronomy Mimeo 76 for thatch control procedures).

5. Core cultivate compacted soils in the spring, and if necessary, repeat core cultivation in the fall.

Fungicides

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Banner, Bayleton, Eagle, Heritage, Rubigan and Sentinel are among the more effective fungicides used for preventive control of summer patch. The initial, preventive application of a fungicide should be applied mid-to-late June in Maryland, followed by a second application 21 to 28 days later. The use rate of Sentinel is 0.33 ounces per 1000 ft2; Heritage is 0.4 oz/1000 ft2; Eagle is 1.2 oz/1000 ft2; whereas, Banner, Bayleton or Rubigan are applied at 4.0 ounces of product per 1000 ft2. Using lower rates will not provide effective control; whereas, higher rates are not likely to provide a significant improvement in summer patch control. Additional applications of fungicide may be required on an as needed basis.

These fungicides should be applied in at least 2.5 gallons of water per 1000 ft2 and when there is a heavy dew on the lawn. Except for Sentinel, watering-in fungicides to wet the soil to a one inch depth may improve fungicide effectiveness. Curative applications of fungicides (with the aforementioned fungicides or Fungo 50 or Cleary's 3336) should begin immediately following observance of disease symptoms. At least two applications of a fungicide, 14 to 21 days apart, will be needed to arrest disease development. It is important to note that the effectiveness of a fungicide will be negated if turf enters a state of drought dormancy. Frequently, the beneficial effects of curative fungicides will not be observed until early autumn when environmental conditions are more favorable for growth and recuperation of injured plants. Lack of preventive control of summer patch with Bayleton indicates that the disease problem may be necrotic ring spot. Necrotic ring spot is controlled with Banner, Fungo 50, Heritage, Eagle and Rubigan, but not Bayleton.

Prepared by Peter H. Dernoeden, Extension Turf Specialist, Department of Agonomy