Lawn Diseases

Although there are many different types of turf-related disease, lawn damage is almost always caused by some kind of fungus. There are a variety of fungi that can affect all species of grass. However, some target specific types of turf such as Bluegrass, Bermuda, St. Augustine, etc. Some fungal infections can be prevented while others can only be controlled.

This fungal infection is common in areas where snow remains on the ground for a long time keeping the grass and soil overly moist. Grayish white or pink mold may be visible on turf just after snow melts but disappears when the grass blades dry. Dead patches of lawn several inches to a foot in diameter are a sign of snow mold. It typically affects Kentucky Bluegrass and Fescue grasses. Good drainage, removal of fallen leaves, and lawn aeration are all effective prevention measures. Tapering off fertilization 6 weeks before the lawn becomes dormant is important. This prevents a last minute grass growth spurt that gives fungus an opportunity to flourish and cause winter lawn damage. The fungus dies out in the spring, so applying fungicide after the damage has occurred serves no purpose.

Red Thread
Fescues and Rye grasses are particularly susceptible to Red Thread fungal infection in the spring and fall when the weather is cool and moist. Pink/red fibers are visible on blades of grass in affected areas. As the grass is overwhelmed by fungus, it will die off and leave brown patches on the lawn.  Keeping thatch to a minimum, ensuring adequate levels of nitrogen and potassium, and aerating the turf regularly all help keep this fungus from taking hold. Good drainage, a morning watering schedule, and the introduction of resistant varieties of Rye grass are also useful. Fungicides such as chlorothalonil and myclobutanil can be used to eliminate Red Thread. Maintaining a soil pH of 6.5-7 is optimal for reducing the risk of recurrence.

Brown Patch
Yellowish brown circular patches of damaged turf 1-3 feet across mixed with a few blades of healthy grass on the surface are a symptom of Brown Patch. Once established, this fungus can rarely be completely eradicated. Watering in the morning instead of the evening, avoiding use of quick-release nitrogen fertilizers, and reducing shade from surrounding landscaping plants can help prevent Brown Patch. Thatch removal and lawn aeration also limit infection. Most residential lawn fungicides can be used to prevent outbreaks. However, only a few such as those containing Azoxystrobin or Myclobutinil are effective for treating an established fungal infection.

Dollar Spot
Kentucky Bluegrass and Bermuda are susceptible to lawn damage from this fungal infection in humid areas. The brown/yellow circles are often small (about the size of a silver dollar). However, they may be spaced very close together covering a large area. Thatch removal, morning watering, and lawn aeration are preventive measures. Low nitrogen can contribute to Dollar Spot infection, so appropriate use of fertilizers is recommended. Many fungicides including contact and penetrating varieties are effective for treatment if used early on. Most require multiple applications.

Kentucky Bluegrass and Rye grasses often suffer from a yellow/orange fungus referred to as Rust. It is unsightly, but only a real danger to newly seeded lawns in the spring. Shaded areas that feature compact soil which is not adequately fertilized are common locations for Rust fungal growth. Frequent mowing, early morning watering, lawn aeration, and removal of grass clippings during mowing are practices that will help prevent Rust or keep it from coming back once eradicated. DMI and QoI (strobilurin) fungicides can be used to stop Rust infestations quickly when combined with proper turf care.

Pythium Blight
Pythium Blight typically appears as matted patches of brown slime on a lawn. Sometimes, white cottony fungal fibers can be detected at the edges. The wet, greasy appearance of the damaged grass is what gives the lawn disease its common name “Grease Spot”. Rapid outbreaks typically occur when the weather is unusually hot and humid. Spots of yellow, red, and brown may spread quickly as the fungus kills large areas of turf. Best practices for Pythium Blight prevention include limiting nitrogen application, watering only in the morning, removing thatch buildup, and frequently aerating the lawn. Mefenoxam was once the preferred chemical for treatment, but some strains of Pythium have developed resistance necessitating the use of alternative fungicides. Even after treatment, a lawn may not fully recover until the next season.

Leaf Spot
Several types of Leaf Spot disease cause grass damage in different varieties of turf. Root rot in Bermuda grass caused by Leaf Spot is fairly common appearing as brown or purple spots that spread quickly. In other grasses, the lawn may turn slightly bluish-gray. Either way, it will look slightly off color when viewed from a distance. Using herbicides too frequently has been linked to the prevalence of this lawn disease in some types of grasses. Too much nitrogen in the soil, lack of aeration, and excess thatch may also contribute. However, the main problem associated with Leaf Spot is usually poor drainage or watering in the afternoon/evening. Instituting a morning watering routine and seeding with resistant grass varieties such as Kentucky Bluegrass are options for managing Leaf Spot. Fungicides containing strobilurin are the chemical of choice for treating this disease.

Fusarium Blight
This blight is also called Summer Patch because of its tendency to strike during hot weather when grass is under stress. Species such as Kentucky Bluegrass that are best suited to cool weather but planted in warm climates anyway are at high risk. When symptoms first develop, the grayish green or tan patches may be donut shaped with a small live patch of grass in the middle. Strands of pink fungus may be seen where the grass stems meet the soil and dark green spots may be apparent on individual blades. Too much nitrogen, thatch, and moisture can prompt the growth of this fungus. Dethatching, a conservative fertilization schedule, and good drainage/watering practices limit the chances of a lawn developing Fusarium Blight. Fungicides are more effective for prevention than for treatment with this lawn disease.

Take ALL Root Rot (TARR) is a disease that typically attacks St. Augustine and Centipede turf. It affects the roots causing stunted growth and eventual destruction of the lawn. Dark spots on the blades of grass and yellow patches of turf are signs of TARR lawn disease damage. Most fungicides have little effect on this fungus after the disease has taken hold. However, fungicides may be used to aid prevention in combination with cultural controls such as appropriate watering, fertilization, aeration, and dethatching. Applying sphagnum peat moss in sufficient quantities to acidify the soil appears to eventually control the disease once the fungus has already spread.

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