Disease Library

Summer Patch

Usually seen on Kentucky bluegrass and fine fescues, this a root disease commonly occurs mid-summer when there are extended periods of high temperatures (greater than 82°F) with wet weather or heavy irrigation. Summer Patch is seen more often in areas that have heavy traffic, poor air circulation, and inadequate drainage. It begins as 2 – 3 inch circular or irregular shaped patches and can get up to 12 inches and can appear yellowish or bronze in color. It can also appear as “frog eye” patches, meaning a circle patch of the diseased turf with healthy turf in the center, giving it a “frog eye” appearance. One way to manage summer patch is by avoiding mowing too – especially during times of extreme heat. Fertilize as recommended and it’s a good idea to aerate and overseed in the fall.

Gray Snow Mold

Occurs during winter or late spring, under snow coverage. You’ll start to notice gray snow mold once the snow melts in the spring. There will be circular areas of light, straw-colored or grayish to white turf. It’s commonly found in areas with the greatest snow accumulation like under snow drifts and along driveways. The damaged turf is often covered in a grayish-white mold (mycelium) with speckled dark flecks. The areas can range from a few inches to a few feet in diameter. This fungus may kill the blades of the plant but will not kill the crown or roots. To help manage gray snow mold, keep mowing well into the fall to avoid tall grass that can fall over and create matting. It’s also a good idea to avoid creating snowbanks from plowing or shoveling.

Pink Snow Mold

Is a lawn fungus that develops under snow cover. Activity of the disease is greatest during periods of wet, humid weather when temperatures range from 32° – 45°F. It forms circular, reddish-brown patches less than 1 – 8 inches in diameter. Under very wet conditions, a white to pinkish covering of mycelia can be seen. To help manage pink snow mold, avoid letting grass grow high as it can fall over and mat under the snow. Avoid creating snowbanks from plowing or shoveling. Remove wet pile of leaves as they are a favorable environment for the disease.

Brown Patch

The grass species that are most susceptible to brown patch are perennial ryegrass, tall fescue, bentgrasses, and sometimes Kentucky bluegrass in mid to late summer during long periods of high temperatures and humidity. Patches of the disease can vary from a few inches to several feet in diameter. It can appear as irregular tan or light brown lesions with dark brown borders. Disease activity of brown patch becomes prevalent when the surface moisture is high, temperatures at night are above 68°F, and daytime temperatures average at 80°F or above. Rainy weather will cause the disease to develop faster. One way to help manage brown patch is by mowing early in the morning to knock dew off the turf.

Dollar Spot

Diseased areas will appear white or tan and can range from 2 – 4 inches in diameter. The spots may also overlap, forming large irregular areas of damaged turf. Individual grass blades may have straw colored bands or lesions with reddish-brown borders. White mycelium may also be seen. Dollar Spot symptoms occur from early to late summer and reaches its peak activity when the temperature is around 80°F with high humidity. Some ways to help prevent the spread of dollar spot is to water the lawn deeply and infrequently and make sure you mow the lawn in the morning. This will knock the moisture off the plant, preventing the fungus from spreading. If possible, collect the clippings after mowing.

Fairy Ring

Appear as rings of dark green, fast growing turf. Thin or dead turf is often found inside or outside of the ring. The circles can range from 4 – 12 inches in diameter, but, when combined, can be a total of up to 200 feet. Sometimes, after rain or irrigation, mushrooms or puffballs will grow in the circular band. To help manage the symptoms of Fairy Ring, continue to fertilize with adequate amounts of nitrogen.

Leaf Spot/Melting-out

Kentucky bluegrass is particularly susceptible to this disease. The first signs of leaf spot and melting-out are small brown spots. As it worsens, the grass blades will expand and become a dark purplish-red oval with a tan center. The spots will enlarge until the entire blade is infected. This disease is active during cool, wet weather between April to early May. Some ways to help manage leaf spot and melting-out include avoiding excessive nitrogen applications in early spring and try to aerate and overseed in the fall.

Red Thread/Pink Patch

This disease develops when temperatures are between 65° – 75° F with prolonged periods of wetness and/or humidity. It will appear the grass to appear reddish or pink in color (hence the name). Some ways to help manage Red Thread and Pink Patch is to apply an adequate amount of nitrogen, do not mow until morning dew has dissipated, and if possible, collect grass clippings after mowing to help prevent it from spreading.

Powdery Mildew

The first sign of powdery mildew is isolated patches of white/gray patches on the upper area of the grass blades. As it progresses, it will cover the entire blade. It may look like it is covered with flour. Favorable conditions for powdery mildew are areas with poor air circulation, high humidity, shade or low light, and cool temperatures. You will usually see this disease in Kentucky Bluegrass. One way to help manage powdery mildew is to reduce shade by trimming surrounding trees and shrubs for better sunlight and air circulation.

Pythium Blight

Also known as grease spot or cottony blight, the first symptoms of this disease are dark irregular-shaped or circular spots. The spots may merge and form large dead areas of turf. The individual grass blades may have a slimy or greasy feel in the morning from dew or at night from high humidity. They may also be covered with white or purplish-gray mycelium. Pythium blight can spread rapidly if conditions are favorable for the disease. Favorable conditions are warm, wet weather (temperatures between 85° – 95°F) You can help manage pythium blight by ensuring the area has good drainage, following proper irrigation practices, and avoiding excessive amounts of Nitrogen when fertilizing


More commonly seen on areas of high-maintenance turf like creeping bentgrass or annual bluegrass on golf courses, anthracnose is diagnosed with a hand lens. The disease produces small, black, pin cushion-like spore structures called acervuli. The roots and crown of the plant can also become affected. This is called basal rot. Symptoms will vary depending on the species of grass, but normally the base of the plant will be dark brown to black in color. As the disease progresses, it will travel up the stem. Some ways to help manage anthracnose is to maintain good soil conditions and fertility, avoid over watering, and improve drainage.
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