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Archive date:  June 9, 2003

Brown Patch Anyone?

A turf disease that poses many problems

If the dreaded dull brown areas in your lawn have become apparent, it is likely that your lawn suffers from brown patch. The following text deals with this late spring scourge and what you can do to deal with this nemesis.

Brown Patch, also called Rhizoctonia blight, is a common infectious disease of turfgrass. All fescue turfgrasses grown in Tennessee lawns can be affected by Brown Patch. However, this disease is usually destructive only in tall fescue during warm, humid weather. While Brown Patch can temporarily harm a lawn's appearance, it usually does not cause permanent loss of turf except in plantings less than one-year old.
Brown Patch disease is sometimes responsible for poor turf quality, but it is not the only cause of brown spots or bare patches in lawns. You may need to consider other possible causes of thinning or dead grass. These may include: improper fertilization,
chemical injury, mower problems, dog or insect injury, localized dry spots, poor soil drainage, excessive thatch, competition from other plants or buried objects.

Tall fescue varieties are the lawn grasses most susceptible to Brown Patch under Tennessee conditions. Fine fescues (hard fescue, creeping red fescue, chewings fescue, and sheep fescue) and zoysia are all moderately susceptible to the disease.

Brown Patch is most destructive when the weather is humid and temperatures are stressful to the grass. Thus, in cool-season grasses such as tall fescue, the disease is most severe under high temperatures (highs above 85 F, lows above 60 F). Conversely, in warm-season grasses such as zoysia, Brown Patch is most severe in humid weather with moderate temperatures (45 - 70 F).

Application of high levels of nitrogen fertilizer, particularly during spring and summer, favors development of Brown Patch by producing lush, succulent growth that is very susceptible to Rhizoctonia infection. Other factors increase disease severity by creating a humid environment favorable for growth of Rhizoctonia fungi. These factors include: overwatering, watering in late afternoon, poor soil drainage, lack of air movement, shade, a high mowing height, and overcrowding of seedlings. Excessive thatch, mowing when wet, and leaf fraying by dull mower blades also can enhance disease severity.

Apply the bulk of nitrogen fertilizer to cool-season turf grasses in fall and early winter rather than spring or summer. Fall fertilization increases overall root growth of cool-season grasses and reduces their susceptibility to several diseases. Do not attempt to cure summertime outbreaks of Brown Patch with nitrogen fertilization, as this will simply aggravate the disease.

When irrigation is necessary, wet the soil to a depth of at least four inches to promote deep rooting. Check the watering depth by pushing a metal rod or screwdriver into the soil. It will sink easily until it reaches dry soil. Avoid frequent, light waterings. These encourage the grass to develop a shallow root system and frequently provide the surface moisture that Rhizoctonia fungi need to infect the leaves.
If a disease outbreak is evident, water early in the day so that the leaves dry quickly. If the lawn is watered late in the day, the leaves may remain wet until morning, thus providing long periods of leaf wetness favorable for infectious fungi. Removing dew, by dragging a hose across the lawn or by very light irrigation during early morning hours, will reduce prolonged leaf wetness and remove leaf exudates that encourage disease development.

Avoid using excessive seeding rates when seeding or renovating a lawn, as overcrowding can aggravate an outbreak of Brown Patch. Selectively prune nearby trees and shrubs to increase air movement and light penetration, thereby allowing leaf surfaces to dry more quickly. Avoid applying herbicides during an active outbreak, as these may aggravate the disease.

In an established lawn, fungicide sprays are not recommended to control Brown Patch. Cultural practices will usually do a great deal to reduce the disease. Even if an outbreak of Brown Patch occurs, crowns and roots of established plants often survive, and blighted turf begins to recover when cooler weather arrives. So an established, well-managed lawn often will recover from Brown Patch without fungicide applications.
Probably the principal situation in Tennessee where judicious use of a fungicide in a home lawn is necessary is to control Brown Patch in a newly seeded lawn of tall fescue. During the summer following a spring seeding, the immature plants can be easily killed by outbreaks of Brown Patch during hot, humid weather. Fungicide sprays may be helpful to protect tall fescue lawns seeded the previous spring, to prevent loss of turf during the first season of growth. Under very high disease pressure, a fungicide spray may even be needed during the first summer following a seeding made the previous autumn, especially if the lawn was sown in late autumn. During the first summer of growth in a new lawn, inspect the lawn regularly during hot, humid weather and be prepared to have a certified pesticide applicator treat the yard if necessary. The most widely available, effective fungicide recommendation is DaconilĀ®.