Click on any
image for a more
detailed view

Disease Management

Brown Patch
Cultural Management: Moisture and temperature are the most common factors limiting brown patch development. While temperature is not easily manipulated in most cases, several things can be done to control moisture availability. Rhizoctonia solani requires a minimum of 10 consecutive hours of leaf wetness or relative humidity ≥95% in order to initiate disease. Practices that reduce the amount of time that the turf canopy is wet or humid will therefore reduce the severity of brown patch.

Irrigation water should be applied infrequently, but in sufficient amounts to meet the water requirements of the turf. Irrigation should be timed so that the duration of leaf wetness is minimized. Early morning irrigation removes large droplets of dew and guttation water, which evaporate slowly, from the foliage and encourages rapid drying of the turf. Avoid irrigation for several hours prior to sunset; this will increase the amount of time that the turf canopy is wet and encourage brown patch development. When syringing turf during the day to reduce heat stress, ensure that the turf canopy dries completely between syringe cycles. If the turf is syringed too frequently, the turf canopy will be constantly wet, creating a perfect environment for development of diseases such as brown patch.

Early morning mowing also reduces leaf wetness duration by removal of large dew droplets and guttation water from the leaves. Alternatively, dew can be removed by dragging a pole, hose, rope, chain, or other object across the turf surface. This practice is known as "poling" or "whipping," and was the first disease control practice commonly used by turfgrass managers.

In areas where sunlight penetration and air movement are low, pruning or removal of surrounding trees and shrubs will help to reduce brown patch development by facilitating water evaporation and improving overall turf vigor. For high maintenance sites, such as golf greens, installation of high-powered fans increases air movement, speeds morning drying of the turf and reduces the incidence of several diseases.

Poor soil drainage also enhances brown patch. Where soil drainage is poor, installation of drainage tile, core cultivation to reduce soil compaction and thatch accumulation, and/or modification of the soil profile to increase porosity will reduce brown patch severity and improve overall turf quality.

Excessive levels of nitrogen fertilizer enhance brown patch activity through two mechanisms. First, high nitrogen produces soft, lush leaf tissue that is easily invaded by fungi such as R. solani. Second, nitrogen increases vegetative growth, therefore reducing air movement in the turf canopy, increasing humidity and leaf wetness. Nitrogen fertilizer should be applied in small quantities during the summer months to reduce brown patch severity.

Chemical Control: Fungicides in the following classes are effective for brown patch control: carboxamides, benzimidazoles, carbamates, dicarboximides, DMI fungicides, nitriles, and Q_O inhibitors. In warm, humid climates, where brown patch pressure is consistent throughout the summer months, preventative, calendar-based applications are recommended for brown patch control. In more temperate climates, where disease development occurs intermittently, applications may be made on a curative basis or according to a disease forecasting system.

Genetic Resistance: Turfgrass species vary significantly in their susceptibility to Rhizoctonia species. Among the bentgrass species used for golf course turf, creeping bentgrass is more resistant to R. solani than colonial bentgrass. For lawn and landscape turf use, Kentucky bluegrass and fine fescue species are often observed to be more resistant to R. solani than tall fescue or perennial ryegrass.

Within some turfgrass species, cultivars vary widely in their susceptibility to Rhizoctonia species. For information on turfgrass cultivars that perform best in your area, consult your local county extension office or visit The National Turfgrass Evaluation Program at: www.ntep.org.

Large Patch
Cultural Management: Control of moisture levels in the thatch and soil is an important aspect of large patch management. The disease is most severe in areas that have poor soil drainage, little air movement, or excessive shade. In areas that are poorly drained, installation of drainage tile, soil cultivation to reduce compaction and thatch accumulation, and/or modification of the soil profile to increase porosity will limit large patch severity and improve overall turf quality. Where air movement and sunlight penetration are low, pruning or removal of surrounding trees and shrubs is recommended. Irrigation should be applied as necessary to meet the water requirements of the turf.

Mowing height may also influence the development of large patch. On zoysiagrass, large patch severity increases as mowing height is decreased from 3.75 cm (1.5 in.) to 1.25 cm (0.5 in.). Reduced mowing heights result in a more dense turf stand, which may create a more favorable environment for large patch development by reducing air movement and increasing humidity in the lower turf canopy.

Chemical Control: Several fungicides are available for control of large patch. Fungicides in the following classes are most effective: carboxamides, benzimidazoles, carbamates, dicarboximides, DMI fungicides, nitriles, and Q_O inhibitors. In turf stands with a history of large patch development, preventative fungicide applications provide excellent control when timed properly. The first application should be made in the fall when conditions become conducive for large patch development, i.e. when the thatch temperature drops below 21°C (69.8°F) for several consecutive days. Subsequent applications should be made as specified on the fungicide label. Because the majority of disease development occurs in the fall, fungicide applications at this time are most important. However, when disease pressure is severe, spring applications may also be required to achieve adequate control.

Genetic Resistance: Little variation in large patch susceptibility is observed among the warm-season grasses. Bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass incur similar amounts of damage due to activity of the pathogen. However, bermudagrass may recover from large patch damage more rapidly than other warm-season species because of its aggressively spreading growth habit. For the most updated information on turfgrass cultivars that perform best in your area, consult your local county extension office or visit www.ntep.org.

Leaf and Sheath Spot
Control of diseases caused by R. zeae and R. oryzae is achieved through means similar to those for brown patch. In laboratory studies, turfgrass isolates of R. zeae were less sensitive to benzimidazole and dicarboximide fungicides than R. solani. Results of a field test in Georgia indicate that these fungicides are less effective than flutolanil and azoxystrobin in suppressing disease caused by R. zeae on creeping bentgrass. Isolates of R. oryzae from rice are also less sensitive to dicarboximides than R. solani in laboratory studies, but turfgrass isolates have not yet been tested. Therefore, accurate identification of Rhizoctonia species is important for selection of fungicides for control.

Yellow Patch
Cultural Management: Like other Rhizoctonia diseases, the severity of yellow patch is enhanced by the presence of moisture in the turf canopy. Increasing soil drainage, air movement, and light penetration into the turf canopy will therefore reduce the severity of this disease. Excessive foliage enhances the incidence of several winter diseases, including yellow patch. Cool-season grasses should be mowed on a regular basis from the time foliar growth begins in the spring until it ceases in the fall. Also, avoid applications of nitrogen fertilizer in the late fall. Because yellow patch occurs during cold weather, irrigation practices are not relevant to the management of this disease.

Chemical Control: Several fungicides are available for the control of yellow patch. Fungicides in the following classes are effective for yellow patch control: carboxamides, benzimidazoles, carbamates, dicarboximides, DMI fungicides, nitriles, and Q_O inhibitors. Adequate control of yellow patch is usually provided by preventative fungicide applications for snow mold diseases.

Genetic Resistance: Few options are available for management of yellow patch with genetic resistance. Yellow patch is most common on golf course greens in temperate climates. In this situation, creeping bentgrass is the only species that is currently available for use. Some improved varieties of creeping bentgrass may have enhanced resistance to yellow patch. For information, consult your local county extension office or visit www.ntep.org

RETURN TO TOP