DISEASES OF TURFGRASSES

ON ATHLETIC FIELDS IN NORTH CAROLINA

Leon T. Lucas

Extension Plant Pathology Specialist - Turf

Electronic version TG03 - Revised May 15, 1995

A number of diseases can cause serious damage to turfgrasses on athletic fields in North Carolina. Many of the problems are caused by fungi and nematodes, but other problems are caused by management and/or environmental factors. An accurate diagnosis is the first and most important factor in the control of turfgrass diseases. Diseases of the commonly used cool season turfgrasses (tall fescue , bluegrass , and ryegrasses ) and the warm season turfgrass (bermudagrass ) used in North Carolina are described along with diseases common to all turgrasses, and methods of disease diagnosis and management. The cool season grasses are used mostly as permanent turf in the mountain regions and ryegrasses are sometimes used overseed bermudagrass in eastern regions of the state. The more cold tolerant bermudagrass cultivars such as Vamont and Midiron are used in the northern regions of the Piedmont.

Tall Fescue Diseases

Brown patch is the most serious disease of tall fescue. The early symptoms of this disease are small circular brown patches about 1 foot in diameter that develop during hot-wet weather. More patches develop and the older patches may continue to enlarge up to 4-6 feet in diameter during hot weather. Lesions that are olive color in the morning when dew is present, or during rainy weather, develop rapidly on young leaves. As the tissue dries the lesions become very light tan. Lesions may girdle leaves causing the portion above the lesion to die. Webby mycelium of the fungus may be seen on the lesions and the surrounding grass blades in the morning or during extended periods of humid and cloudy weather in the summer. Vigorously growing plants that have received higher than recommended rates of nitrogen fertilizer during the spring are more susceptible to the disease. Tall fescue established less than one year can be completely killed by this disease. Affected areas may need renovating to correct soil pH and fertility problems and replanting in September or October. Well-established fields may be damaged during the summer months, but with proper maintenance (proper soil pH, low nitrogen levels in the summer, infrequent irrigation, regular mowing when the grass is dry, and fall fertilization) the grass will usually recover during the fall. Fungicides such as Daconil 2787, Dyrene, Tersan 1991, or Fore applied once every 3 weeks during favorable weather conditions for disease development will give good control of brown patch. This treatment is expensive and should not be needed on athletic field if the tall fescue is managed properly.

Helminthosporium net blotch occurs on tall fescue but usually does not cause severe damage. The symptoms of this disease are dark brown "net" patterns on the leaves. Young seedlings may be killed by the disease, but old plants will usually overcome the damage during favorable growing periods.

Rust occurs on tall fescue and is seen most often in late summer. The symptoms of rust on tall fescue are small yellow spots on leaves with masses of yellow to rust colored microscopic spores in the center of the spots. The number of spots may become so numerous that the entire leaf becomes yellow and dies slowly. The turf will recover from rust during favorable growing conditions. Drought and heat during the summer can damage tall fescue. Seedlings that are less than one year old may be killed by drought. Old tall fescue plants may go dormant during dry weather in summer and turn yellow or brown. Many of these plants will resume growth during cooler weather when adequate moisture is present. Young tall fescue fields need irrigating during hot-dry weather. Older, well established fescue will remain greener with irrigation. In both cases, irrigate infrequently (once every week during dry weather) and enough water should be applied to wet the soil at least 6 inches deep. A good management program to encourage the development of a healthy root system in the fall and spring will help tall fescue tolerate hot and dry weather.

Bluegrass Diseases

Helminthosporium leaf spot occurs frequently on bluegrass. The leafspot symptoms are small dark spots on the leaves that increase in number and size and cause the leaves to die. Leaf-spots develop in the spring and often continue to develop throughout the summer and fall. The disease will cause a brown color and will reduce the vigor of the turf. Some of the fungi that cause leafspots cause root and crown rots that result in melting-out or fading-out in the summer. Broad spectrum fungicides such as Daconil 2787 or Chipco 26019 can be used to control these diseases in the spring before leafspot symptoms become severe. Good management programs that avoid excessive rates of nitrogen and use of irrigation infrequently, but enough each time to wet the soil 6 inches deep to prevent water stress will help prevent damage from Helminthosporium diseases on bluegrass. Some of the new bluegrass varieties have more resistance to these diseases and should be used.

Red thread is a common disease on bluegrass in the mountains during summer. The symptoms of the disease are small circular brown areas .5 to 1 foot in diameter. The symptoms are very similar to brown patch that sometimes develops on bluegrass. Red thread can be identified by the presence of a small "red thread" of the fungus that causes the disease at the tip of many of the dead leaves. Small amounts of nitrogen fertilizer can be used to stimulate bluegrass to overcome the disease. Some fungicides can be used to control the disease.

Rust is a serious disease on some bluegrass varieties. The symptoms of rust are small yellow or brown spots on leaves that enlarge and increase in number until entire leaves are affected. Masses of orange to rust colored microscopic spores develop on the lesions. Affected leaves die slowly giving the turf a yellow to brown appearance. The turf will usually become thin and may be more susceptible to other diseases and weed invasion. If a white cloth is rubbed on the affected turf, a rusty color which are the spores will be present on the cloth. Broad spectrum fungicides can be used, but the best control is the use of improved varieties and good management programs.

Southern blight is a disease that occurs on bluegrass in the mountains of North Carolina. The symptoms of this disease are dead circular areas .5 to 3 feet in diameter that usually have a tuft of green grass in the center. The disease develops rapidly during hot and wet weather. Even clover and other weeds in the affected spots are usually killed by the fungus. White masses of the fungus and small yellow sclerotia of the fungus are usually present near the soil surface at the advancing edge of the spots. Bluegrass usually spreads back into the spots with good management.

Dollar spot sometimes occurs on bluegrass and appears as small circular spots 2-4 inches in diameter. A cottony growth may be present in the morning on leaves in affected spots. Good management practices and the use of small amounts of nitrogen will help overcome the effects of this disease.

Ryegrass Diseases

Diseases discussed under tall fescue and bluegrass such as brown patch, red thread, Helminthosporium diseases, dollar spot, and rust occur on perennial ryegrasses with similar symptoms. Some ryegrass cultivars are very susceptible to rust

Pythium blight and brown patch are often serious problems on ryegrasses used to overseed bermudagrass in eastern North Carolina. Symptoms of Pythium blight are rapid death of seedlings in circular to oblong areas during warm-wet weather. Sometimes gray masses of the fungus may be present in the affected areas giving the condition called cottony blight. Planting ryegrasses in the fall when the weather is cooler will help avoid damage from these diseases. Also, treatment of seeds before or soon after planting with certain fungicides, such as Subdue or Koban will give good control. Proper watering will help prevent these diseases and improve seedling survival.

Bermudagrass Disease

Spring dead spot is a serious disease of bermudagrass on some athletic fields. Symptoms of this disease are small circular dead spots .5 to 2 feet in diameter in the spring as bermudagrass resumes growth from winter dormancy. This disease usually develops in 4 to 6 years old bermudagrass that has been managed at a high level. Bermudagrass grows over the spots slowly, or weeds invade the affected spots, during the summer. The spots may occur in the same place and enlarge for 2 or 3 years and then disappear. Factors associated with development of this disease are high rates of nitrogen fertilizer and accumulation of excess thatch. An application of the fungicide, Tersan 1991, at 8 oz. per 1000 sq. ft. in October or Rubigan at 6 oz per 1000 sq. in September to turf that was affected in the spring has given good control of this disease the following spring. Management practices that use lower rates of nitrogen and thatch removal will help prevent spring dead spot.

Nematodes which are microscopic eel-like worms in the soil, can cause serious damage on bermudagrass, especially in sandy soils in southeastern North Carolina. Several nematodes including sting, ring, stunt, lance, stubby-root, and spiral nematodes are commonly found in soil from bermudagrass turf. Serious damage to bermudagrass has been associated with the sting nematode. The symptoms of damage by the sting nematode are poor turf that does not respond quickly to nitrogen fertilizer and wilts quickly during dry weather. The roots are stunted and very shallow. Nematicides will control the sting nematode, however, nematicides are very toxic and must be applied by licensed applicators. A good management program that includes fertilizer and irrigation to prevent drought stress will help bermudagrass overcome the effect of these nematodes.

Dollar spot is sometimes a problem on bermudagrass turf in late summer. Symptoms of this disease are small brown spots 1 to 3 inches in diameter. The spots may become so numerous that the turf has a general brown appearance. The disease usually develops on bermudagrass turf that has not been fertilized adequately with nitrogen. The use of good management practices including proper amounts of nitrogen and water will help bermudagrass overcome this disease.

Other Problems On All Types Of Turfgrasses

Fairy rings cause dead, green, or a combination of dead and green rings in turf from a few to many feet in diameter. Mushrooms may be present in the dead or green rings at certain times of the year. Sometimes fairy rings occur as rings of mushrooms without any apparent effects on the turfgrass. The rings occur in the same area for a number of years and enlarge a few inches or feet each year. The fairy ring fungi grow in the soil and cause the green rings by releasing nitrogen from organic matter, or kill the grass by releasing toxins into the soil or preventing water from entering the soil. The fungi usually begin growing on some source of organic matter such as old stumps buried in the soil. Removal of soil from affected rings and replacement with clean soil and replanting with healthy grass is recommended, but is usually not practical. Rototilling the soil in and around the rings and replanting healthy grass has controlled fairy rings in some cases. Loosening of the soil and watering the area frequently may help control some fairy rings. Grasses that spread rapidly such as bermudagrass often will spread into the affected areas whereas grasses such as tall fescue may be killed and areas fill in with weeds.

Slime molds appear as a grayish growth on grass leaves in small circular spots. These fungi produce a slimy growth on the leaves in wet weather that develops into a powdery mass of spores. Slime molds can shade the leaves, but usually do not cause serious damage. The fungi can be removed by brushing or mowing the fungus off the affected leaves.

Algae are single celled plants that grow on the surface of wet soils. Algae may appear as a black slimy growth on the surface of a poorly drained soil in wet weather and may crack and curl when the soil becomes dry. It is usually a problem in an area that does not drain properly and may have a low soil pH. Algae can be controlled by correcting soil drainage and soil nutrient problems.

Soil compaction is probably the most serious problem on athletic fields and causes poor growth of turfgrasses. Compaction results from traffic such as practicing, playing or marching on the fields. Proper oxygen and water relations in the soil for turfgrasses are disrupted by the soil particles being pressed together. The soil should be loosened by renovating or aerifying to relieve the compaction for better growth of turfgrasses. Limiting access for the use of athletic fields must be a part of a good turf management program

Diagnosis And Management Of Diseases

Diseases and other problems can be diagnosed by using the descriptions given in this and other publications. Assistance in identification and control recommendations can be obtained from your local Agricultural Extension agent. Soil samples should be taken regularly to identify nutritional and nematode problems. Pesticide and fertilizer suggestions are updated annually in the N. C. Agricultural Chemicals Manual, which would be a good reference. Many different diseases and problems occur on turfgrasses in North Carolina because of the diverse climatic regions in the state. The selection of the best turfgrass and proper management program will help prevent and overcome many of the diseases.