IDENTIFICATION AND MANAGEMENT OF BROWN PATCH DISEASE

Agronomy Mimeo 65Revised February, 1996

 

INTRODUCTION

Brown patch or Rhizoctonia blight is a common summertime disease of cool-season turfgrasses, which is caused by the fungus Rhizoctonia solani. The pathogen attacks nearly all grasses used as turf, but is most damaging to tall fescue, perennial ryegrass, creeping bentgrass and annual bluegrass. Kentucky bluegrass, zoysiagrass and other species are occasionally injured by R. solani. Another species of the fungus, Rhizoctonia zeae, is a more potent agent of brown patch which is primarily found attacking perennial ryegrass grown on golf courses. In zoysiagrass, brown patch tends to be an autumn disease, and is uncommon in Maryland

 

SYMPTOMS

The symptoms of brown patch vary according to host species. On closely mown turf such as bentgrass, blighted patches are generally circular and range from three inches to three feet or greater in diameter. During early morning hours when there is dew, the outer edge of the patch may develop a one to two inch wide smoke ring. The smoke ring is blue-gray in color and is caused by Rhizoctonia mycelium in the active process of infecting leaves. Smoke rings are not always present and patches may have an irregular rather than circular shape. Close inspection of leaf blades reveals that the fungus primarily causes a die-back from the tip down, which gives affected turf its brown color. In tall fescue, perennial ryegrass, and Kentucky bluegrass affected areas are frequently irregularly shaped and smoke rings are only occasionally present. R. solani produces distinctive and often greatly elongated lesions on tall fescue leaves. The lesions are a tan or chocolate brown color, and are bordered by narrow, dark brown bands of tissue. In perennial ryegrass and Kentucky bluegrass smaller leaf lesions are produced and tip die-back commonly occurs. During early morning hours, when the disease is active, the cobweb-like mycelium of R. solani may be observed on leaves in the presence of a heavy dew.

 

PREDISPOSING CONDITIONS

Environmental conditions that favor disease development in cool-season grasses are day temperatures above 85F and high relative humidity. A minimum daily temperature above 61F in combination with either rainfall or relative humidity above 95% for more than 8 hours are the most critical environmental requirements for disease development. Evening or nighttime thunderstorms from mid-June to late September and a minimum air temperature above 68F are most conducive for severe brown patch. Weather conditions that result in little or no dew formation (i.e., low relative humidity or low soil moisture) or cool nighttime temperatures (i.e., less than 63F) will result in a marked reduction in brown patch severity. Late spring and summer application of nitrogen fertilizers, in particular water soluble nitrogen fertilizers such as urea and ammonium-based products, increase brown patch severity. Evening or nighttime watering or showers will greatly increase disease injury.

 

CULTURAL AND CHEMICAL CONTROL

Home lawns or athletic fields composed of tall fescue or perennial ryegrass turf are likely to be injured by brown patch during July and August. Young tall fescue or perennial ryegrass stands (during the first year of growth) are particularly susceptible to severe brown patch injury. Generally, R. solani blights leaves and sheaths, but does not kill crowns or roots. Lawns and athletic fields that are properly fertilized, irrigated and maintained at the recommended mowing height usually recover from brown patch in September. Initiating nitrogen fertilizer applications in mid-September and ensuring that blighted stands are not subjected to severe drought stress that cause turf to become dormant will help to promote more rapid turf recovery. Turfs that have been severely thinned-out due to a combination of heat and drought stress, or disease and insect pests may need to be overseeded in September. Fall fertilization (i.e., 75 to 100% of the total amount of annual nitrogen applied between September and mid-November), irrigating early in the day, and mowing turf to avoid a very high canopy are cultural practices that help alleviate brown patch. Use of slow release nitrogen sources such as IBDU, methylene urea, sulfur coated urea and natural organics in the fall also help to further reduce the severity of brown patch the following summer. On golf course fairways, it helps to collect clippings and mow early in the morning to speed drying of the foliage.

Younger stands, as well as mature turf during extended periods of high nighttime temperature and humidity, may require fungicide treatment. Fungicide treatment may be needed two to three times on tall fescue lawns in summer to protect turf from extensive blighting during high disease pressure periods (i.e., hot, humid, plentiful moisture). Perennial ryegrass should not be used as a lawn grass in Maryland because it is very susceptible to brown patch and numerous other diseases. Fungicides should only be applied by an experienced applicator. Homeowners do not have the proper equipment to apply most fungicides and many of the more effective materials are not available for purchase by homeowners.

On intensively managed golf course putting greens, tees and fairways, fungicides are frequently applied on 10 to 14 day intervals during peak disease pressure periods from late June to early September. Some effective fungicides for brown patch control are as follows: Chipco 26019, Cleary's 3336, Curalan, Daconil 2787, Eagle, Fore, Heritage, Lynx, ProStar, Sentinel, and Touche. Most fungicides would be expected to provide about 10 to 14 days of brown patch control during high disease pressure periods. Heritage (0.2 oz/1000ft2) or ProStar (2.0 oz/1000ft2), tank-mixed with either Banner (1.0 fl. oz/1000ft2), Bayleton (1.0 oz/1000ft2), and some other fungicides would be expected to provide brown patch control for 21 days or longer. Heritage and ProStar should be used in tank-mix combinations with another fungicide because this practice increases the number of diseases controlled and can extend residual effectiveness. For any fungicide or combination of materials to provide their maximum benefit, they should be applied at the onset of disease symptoms and prior to any significant turfgrass blighting. Remember, a shift in weather to cool nighttime temperatures or very dry soil and atmospheric conditions will greatly reduce disease activity, and will help to reduce the frequency of fungicide application. See Agronomy Mimeo 84 "Diagnosing Common Lawn Disease" and Agronomy Mimeo 80 "Maryland Turfgrass Disease Control Recommendations" for more information about brown patch and its control. References to trade names do not constitute an endorsement, guarantee or warranty by the University of Maryland. No discrimination is intended against products not mentioned.

Mimeo prepared by Peter H. Dernoeden, Extension Turfgrass Specialist, Department of Agronomy