Brown Patch & Large Patch Diseases of Lawns

Introduction

Brown patch and large patch are probably the most common and damaging diseases of cool-season and warm-season turfgrasses, respectively, in South Carolina. The beauty of all South Carolina lawn grasses can be quickly destroyed by these diseases, which are each caused by a different strain of the fungal pathogen, Rhizoctonia solani. These diseases can rapidly develop when there is an extended period of leaf wetness, and the temperatures are suitable for disease development.

Generally, symptoms of brown patch begin on cool-season grasses (tall fescue, ryegrass, bluegrass, and bentgrass) during the late spring and can continue during the summer. It may also occur on these grasses during warmer periods of the winter months.

Warm-season grasses most commonly affected by large patch are centipedegrass, zoysiagrass, and St Augustinegrass. Typically, bermudagrass is not as severely damaged as are the other warm season turfgrasses because its rapid growth and spread allows it to recover more quickly. The fungus causing large patch disease is most active during the late fall and again during the spring. However, most symptom development occurs in spring during the green-up of the lawns.

Symptoms

Symptoms of brown and large patch diseases may vary greatly with the type of grass and soil conditions. The diseases usually cause thinned patches of light brown grass that are roughly circular in shape. These areas range in diameter from a few inches to several feet. Damaged areas may coalesce or merge. Many times the turfgrass in the center of the patch will recover, resulting in a doughnut-shaped pattern. However, during conditions that are favorable for rapid disease spread, large areas of the lawn may be thinned and killed without the formation of noticeable circular patches. This type of pattern is commonly seen on infected St. Augustinegrass when grown in shady, moist locations.

Large patch of centipedegrass often results in a rounded pattern of dying turfgrass as the disease-causing fungus moves outward in all directions.
Gary Forrester, ©2020, Horticulture Extension Agent, Horry County, Clemson Extension

Large patch disease often becomes evident in the spring, as St Augustinegrass (above) and other warm season turfgrasses green-up. The center of this diseased area has begun to recover as the fungal activity is moving outward and because the disease primarily targets the above ground portion of the turfgrass.
Matthew Zidek, Texas A&M AgriLife Extension Service, Bugwood.org

Brown patch on turfgrass tall fescue lawn often has a smoky brown perimeter where there is active fungal growth.This coloration may be more apparent during the early morning hours.
Joey Williamson, ©2015 HGIC, Clemson Extension

Infected warm-season grasses rarely have leaf spots but instead have rotted leaf sheaths (where the leaf blades attach to the stem) near the soil surface. Therefore, it is diagnostic for the disease if one tugs gently on the leaves in the recently discolored perimeter and the blades pull free.

Close inspection of cool-season grass blades reveals small, irregular, tan leaf spots with dark-brown borders. Bentgrass may not show individual lesions, but leaves will turn brown and shrivel. Newly seeded tall fescue in the spring is more susceptible and more easily killed than mature fescue seeded in the fall.

Grasses Commonly Affected

All types of warm-season or cool-season lawn grasses grown in South Carolina can be affected by large patch or brown patch, respectively. Unfortunately, there are currently no turfgrass species entirely resistant to these diseases available.

Brown patch is the most common and important disease of tall fescue in the Southeast. In most cases, affected areas of mature turfgrass are able to recover, but tall fescue lawns less than a year old can be killed. Kentucky-31 tall fescue, which was once a more commonly planted turfgrass for home lawns, has more resistance to brown patch than all turfgrass tall fescue cultivars. Large patch is the most common disease affecting centipedegrass, although all warm-season turfgrasses are susceptible.

Prevention & Treatment

The best way to prevent brown patch or large patch in the home lawn is by following good lawn care practices. This is much easier and less expensive than the use of fungicides and can be very effective.

• Avoid high rates of nitrogen fertilizer on cool-season grasses in the late spring and summer. Avoid high nitrogen rates on warm-season grasses in mid-to-late fall or early spring before the lawn fully greens up. The disease-causing fungus readily attacks the lush growth of grass, which nitrogen promotes. Avoid fast-release forms of nitrogen fertilizer.
• Irrigate grass only when needed and to a depth of 4 to 6 inches (generally 1 inch of irrigation water per week), but do not subject the lawn to drought conditions. Water the lawn early in the morning. This disease can spread fast when free moisture is present, especially greater than 10 hours of continuous leaf wetness. For more information on irrigation, please see HGIC 1207, Watering Lawns.
• Avoid spreading the disease to other areas. Remove clippings if the weather is warm and moist to prevent spread to other areas during mowing. Mow the lawn after the morning dew has dried and mow the diseased areas last.
• Keep lawns mowed on a regular basis and to the proper height for the turfgrass species. Mowing the lawn lower than the optimum mowing height can increase disease severity, as can mowing too high, which slows the leaf drying time. Do not mow fescue lawns shorter than 2½ inches high, nor higher than 3½ inches. Mow centipede at 1½ to 2 inches high. For more information on turfgrass mowing heights, please see HGIC 1205, Mowing Lawns.
• Provide good drainage for both surface and subsurface areas. Correct soil compaction by core aeration. Prevent excessive thatch buildup. For more information on aeration and dethatching lawns, please see HGIC 1200, Aerating Lawns, and HGIC 2360, Controlling Thatch in Lawns.
• Have the soil tested and apply fertilizer and lime according to soil test recommendations. Disease may be more severe if the soil pH is less than 6.0 (except for centipedegrass). Keep the soil potassium (K) and calcium (Ca) levels at the upper end of the “sufficient” ratings on soil tests. For more information on having the lawn soil tested, please see HGIC 1652, Soil Testing.

Fungicides can be difficult to rely upon for controlling brown patch and large patch in the home lawn, but regular applications can vastly improve the lawn appearance.

Preventatively, fungicides should be applied to turfgrass tall fescue in the spring and early summer. Frequently brown patch symptoms become obvious around the first week of May in the Upstate. Curative treatments may need to be made regularly during the summer if rainfall is frequent.

Warm season turfgrasses also require fungicide treatments in the spring but are especially important in the fall for best disease control. Although the large patch fungus is active in the cooler weather of fall, symptoms usually are more prominent in the spring as the warm season turfgrasses are greening up. Make the first application on warm season turfgrasses in early October for the fall and repeat the application approximately 2 to 4 weeks later, but before the turfgrass goes dormant. Re-apply a fungicide treatment in April for the spring application.

Typically, applications are made at 14- to 28-day intervals, depending upon the fungicide. If the disease is severe enough to warrant chemical control, select one of the following fungicides listed in Table 1. It will help in disease control to alternate fungicides used with each subsequent application to prevent a buildup of resistance to a fungicide. Slightly better control may be obtained by a liquid spray fungicide application rather than by a granular application of the same fungicide active ingredient. Granular fungicides are easier to apply, but they must be irrigated after application with ½ inch of irrigation water or rainfall (follow product label directions).

Table 1. Fungicides for Control of Brown Patch & Large Patch on Home Lawns

Pesticides are updated annually. Last updates were done on 07/22 by Adam Gore.

Originally published 06/99