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Turf Disease Identification

Adapted from

Algal scum


Scientific Name: (algae - Nostoc spp., Oscillatoria spp., Chlamydomonas spp., Hantzchia spp., others)
Description: Rather than infecting turfgrass it instead is highly invasive and competes with grass for space in wet or shaded environments. It affects wet areas with poor air circulation and compacted soils, and it's growth is encouraged by extended periods of rainy, overcast and warm weather. The disease slows water infiltration, keeps thatches wet for extended periods of time, and impedes oxygen and other gas diffusion into and out of soils.
Management: Alleviate wet soil conditions by improving drainage, aeration, and proper irrigation practices. Improve air circulation by selective pruning or removal of trees and shrubs.



Scientific Name: (fungus - Colletotrichum graminicola)
Description: May kill plants in irregularly shaped patches from several inches to many feet in diameter. The overall color of affected patches goes from reddish brown to tan. Crown tissues become infected and plants yellow and die. The fungus occasionally causes reddish brown spots on leaves that then turn yellow and finally light tan to brown as they die. Grayish black mycelial mats are often found on lower sheath tissue and stems. Tiny black fruiting bodies (acervuli) form in dead leaves or stems.
Management: Proper fertility, alleviating soil compaction and traffic, and providing adequate soil moisture. Avoid applying high rates of nitrogen during periods of drought or high temperature. Avoid watering during the late afternoon or evening.

Bipolaris, Drechslera and Exserohilum Leaf Spot, Crown and Root Rot


Scientific Name: (fungi - Bipolaris cynodontis, Drechslera gigantea, Bipolaris stenospila, Curvularia spp. and Exserohilum spp.)
Description: Develops during warm weather when cyclical patterns of wetting and drying occur in the thatch layer. Symptoms often appear on leaf blades (leaf spots) in cool weather and as crown and root rots (melting-out) in hot humid weather. In early stages, severely affected turf has a purple cast and the turfgrass thins. Often the condition becomes advanced before a disease is suspected and verified by the presence of leaf spots. Fading-out is most prevalent on turfgrass weakened by other disease-causing organisms, insect pests, nematodes or improper cultural practices. Small, brown-to-purple lesions with tan centers occur on leaf blades. Leaf spots are commonly found near the collar area of the leaf blade. Severely affected leaves turn reddish-brown, then wither and die. When temperatures exceed 85 F or under severe disease conditions, a sheath and crown rot may occur with turfgrass killed in patches.
Management: Maintain adequate fertility, giving special attention to levels of nitrogen and potassium. Aerate to eliminate soil compaction. Provide good drainage. Avoid herbicide applications during periods of disease activity. Water adequately, but not excessively or too frequently. Mow at the proper height. Avoid thatch build-up. Preventive fungicide applications are more effective than treating a severe outbreak.

Fairy Rings

Fairy Ring

Scientific Name: (fungi - Agaricus spp.,Marasmius oreades)
Description: Grows in circles or crescent-shaped areas, ranging from a few inches to 50 feet in diameter, feed on organic matter in the soil and thatch layer. Areas previously covered with trees or fill which contained stumps or logs are prime candidates. They are either dark green or brown. Brown rings develop when fungal mycelium forms a hydrophobic layer. This layer prevents water from reaching turfgrass roots, resulting in drought stress. Turfgrass next to the ring may be dark green because of nitrogen released from organic matter on which the fungus is feeding. Mushrooms may or may not develop after a period of heavy rainfall or irrigation.
Management: Vertical mowing and topdressing to reduce thatch and removal of tree stumps and roots reduce the organic matter on which the fungus feeds. Fertilization may mask dark green fairy rings by stimulating growth in the rest of the turf. Aeration and drenching the soil with a wetting agent will minimize development of the zone of brown or dead grass in the area of dense mycelial growth. Difficult to control with fungicides since soil in the infected area is almost impervious to water. Sporadic success has been achieved by aerating and drenching with fungicide.

Pink Snow Mold


Scientific Name: (fungus - Microdochium nivale)
Description: Pink snow mold occasionally is a problem during extended periods of cool, wet weather with or without ice or snow cover. Patches occur as reddish-brown spots ranging from an inch to several inches in diameter. Sometimes a pink fungal mycelium may be seen at the advancing edge of the spot.
Management: Lush growth will make the turf more susceptible to snow mold. The last application of nitrogen should be early enough to give the turfgrass a chance to harden off before the grass becomes dormant. Contact fungicides provide adequate control.

Powdery Mildew


Scientific Name: (fungi - Erysiphe spp.)
Description: Powdery mildew is especially common on annual grasses used for overseeding. It spreads rapidly in shaded areas. Powdery mildew appears as a grayish-white fungal growth on the upper surface of leaves and leaf sheaths. Infected leaves turn yellow and gradually die. Repeated infestations result in eventual death of plants. Surviving plants are weakened.
Management: Reduced shading and increased air circulation will help control powdery mildew. Where these conditions cannot be changed, fungicides are available for control.

Pythium Blight, Cottony Blight, Greasy Spot


Scientific Name: (fungus - Pythium aphanidermatum)
Description: Disease is favored during rainy, foggy weather and in low lying areas where air circulation is poor. Roundish, dark, greasy to slimy patches of matted grass, from two to 12 inches in diameter, appear suddenly. On close-cut turf, pythium blight may appear as streaks that follow water drainage or mowing patterns. When disease is very active, fungal mycelium grows profusely over affected plants so that diseased areas have a cotton-like appearance. Hybrid bermudas are more susceptible to pythium than common bermudagrass. Pythium may cause seedling blight and poor stand development in perennial ryegrass overseedings. It also can cause crown and root rots which generally occur in early spring or late fall when soils are cool and excessively wet or saturated. Symptoms of Pythium root rot mimic melting out and anthracnose and there is no foliar mycelium. Diagnosis should be confirmed by a diagnostic laboratory as soon as possible.
Management: Good water management is critical. Avoid late day watering and overwatering new plantings. Remove thatch with frequent verticutting and avoid overfertilization. Improve soil drainage and aeration. Increase air movement by reducing shading, selective pruning or fans. Increasing the mowing height and other practices that promote root growth may lessen the damage from Pythium root rot. During extended periods of warm, humid weather, a preventive fungicide program is advised. Fungicide control of Pythium root rot is less consistent than control of foliar blight. If extensive damage appears, turf seldom responds to fungicide treatment.



Scientific Name: (fungus - Puccinia cynodontis)
Description: Bluegrass, ryegrass and zoysiagrass are most commonly affected. Rust diseases are favored by warm humid conditions and develop most frequently on grasses stressed by drought conditions, low nitrogen fertility and shade. Disease first appears on leaves as small orange to reddish-brown flecks that enlarge to form raised pustules. Individual pustules are usually oval or elongated and contain a powdery mass of orange to reddish-brown spores. As pustules mature, they turn brown to black. Heavily infested turf becomes thin with an overall yellow-orange to reddish-brown color. Infected leaves turn yellow, wither and die.
Management: Maintain adequate nitrogen levels, avoid moisture stress or overwatering and adjust mowing heights according to turf requirements. Use rust resistant varieties. Fungicides are available for rust control.

Necrotic Ring Spot


Scientific Name: (fungus - Leptospheria korrae)
Description: Circular patches over a foot in diameter appear in the spring, fade with warmer temperatures and then reappear with heat and drought stress. Initially, leaves are purplish colored and wilted. Plants die and turn straw colored. Because roots, crowns and rhizomes are rotted, plants are easily removed from turf. Two- to three-year old patches may have a frog-eye appearance where plants have survived or recolonized the middle of the affected area. The fungus is active in the cool wet weather of spring and fall.
Management: Adequate fertilization is required. Complete fertilizers containing phosphorus and potassium as well as slow release nitrogen carriers are the most effective. Daily irrigation, applied midday, cools the turfgrass and allows infected plants with depleted root systems to survive the late afternoon heat stress. Early spring applications of fungicides reduces severity but may not completely control the disease. Fungicides need to be drenched into the soil before they dry on the foliage because this is a root disease. DMI fungicides like fenarimol and propiconazole, which when used at the high rate necessary to control necrotic ring spot, slow down plant growth. So while they may control the fungus, recovery of the turf is not evident.

Maintenance Details

2 to 4: Weeks, the length of time that systemic fungicides may protect plants and protect new growth.

7 to 14: Days, the length of time that contact fungicides typically protect turfgrass. This type of fungicide does not protect new foliage.

Source: Penn State University

6.5 to 7: pH, the recommended maintenance level for soil where red thread has been a problem on turfgrass.

Source: Cornell University

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June 18, 2019, 8:44 am PDT

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