Turf Diseases

Algal scum

(algae - Nostoc spp., Oscillatoria spp., Chlamydomonas spp., Hantzchia spp., others): Algae do not infect turfgrasses but they are highly invasive and often out-compete grasses for space in wet or shaded environments. Algal scum can be a chronic problem on greens, especially those with poor air circulation, compacted soils and wet areas. Their growth is encouraged by extended periods of rainy, overcast and warm weather. Algal scums slow water infiltration, keep thatch wet for extended periods of time, and impede oxygen and other gas diffusion into and out of soils.

Management: Control requires alleviating wet soil conditions by improving drainage, aeration, and proper irrigation practices. Improve air circulation by selective pruning or removal of trees and shrubs. Chemical applications must be done carefully since many will cause severe burning of turf.

Anthracnose

(fungus - Colletotrichum graminicola): Anthracnose 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. Leaves 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: Cultural practices that reduce disease include: proper fertility, alleviating soil compaction and traffic, and providing adequate soil moisture. Do not apply high rates of nitrogen during periods of drought or high temperature. Water turf deeply and as seldom as possible to avoid stressful conditions. Avoid watering during the late afternoon or evening. Fungicides may hasten recovery of affected turf.

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

(formerly Helminthosporium) (fungi - Bipolaris cynodontis, Drechslera gigantea, Bipolaris stenospila, Curvularia spp. and Exserohilum spp.): Helminthosporium type diseases develop during warm weather when cyclical patterns of wetting and drying occur in the thatch layer. Symptoms (photo) 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: The following cultural practices all contribute to healthy grass that resists development of weak pathogens: 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.

Fungicide applications hasten recovery of affected turf. However, they should be used in combination with good cultural practices. Preventive fungicide applications are more effective than treating a severe outbreak.

Brown Patch

(fungus - Rhizoctonia solani): The name, brown patch, is not very descriptive of the varied symptom expression caused by Rhizoctonia spp. on turfgrass. Symptoms differ on cool- and warm-season grasses and vary depending on environmental conditions and cultural practices (photo).

Turfgrass affected by brown patch generally will exhibit circular or irregular patches of light brown, thinned grass. On cool-season grasses (bent, rye and fescue) during periods of warm, humid weather, a darkened border or smoke ring may develop at the outer margin of the patches. The smoke-ring symptom is not reliable for diagnosis.

Symptoms on warm-season grasses such as bermudagrass or St. Augustinegrass include circular to irregular patches of blighted turf. Patches up to several yards in diameter commonly develop in the fall, winter and spring when these grasses are approaching or emerging from dormancy, evening temperatures are below 68 ^oF, and rainfall usually increases. Active infections are noticeable by yellow leaves at the edges of patches. Leaf sheaths become rotted, and a gentle tug on the leaf blade easily separates the leaf from the runner. Brown patch usually does not discolored roots. Disease develops most rapidly when air temperatures are between 75 and 85 ^oF and wet conditions are present and generally subsides when air temperatures rise above 90 ^oF.

Management: Water only as needed and early in the day to remove dew and allow the grass to dry quickly. Avoid over fertilization in spring and fall. Improve the turfgrass root system with good drainage and aeration to reduce damage caused by brown patch. Fungicides are most effective when used on a preventive basis.

Dollar Spot - Small Brown Patch

(fungus - Sclerotinia homeocarpa): Bentgrass, hybrid bermudagrasses and zoysiagrass are most susceptible to dollar spot (photo). Disease occurs from late spring through fall and is most active during times of warm humid days (70 to 85 ^oF) and cool nights (60 ^oF). Water, mowers and other equipment or shoes spread the fungus.

On fine textured and close-cut turf, round, bleached out or straw-colored patches occur which are sunken and approximately the size of a silver dollar. In coarse textured or high-cut turf, the dead spots are larger and more diffuse. Under these conditions, dollar spot is sometimes confused with brown patch. Characteristic spots on leaf blades readily distinguish dollar spot from brown patch. Light tan spots with reddish-brown borders radiate from the edge of the leaf blade. These spots may cover the width of the leaf. When the disease is active, cobweb-like mycelium of the fungus can be seen growing on affected areas early in the day before dew dries.

Management: Remove excess thatch. Maintain proper fertility and adequate soil moisture. Aerate compacted soils. Remove morning dew by poling, irrigating or mowing. Choose a less susceptible turfgrass. Dollar spot seldom damages St. Augustine and centipede grasses. Fungicide applications are most critical during moist weather in spring and fall when day temperatures are between 70 and 80 ^oF.

Downy Mildew

(fungus - Sclerophthora macrospora): Leaf blades have white or yellow-green linear streaks running parallel to the leaf veins (photo). Leaves turn yellow and there may be some browning of leaf tips. The disease is disfiguring and growth may be stunted. The disease is usually more severe in moist shaded areas.

Fairy Rings

(fungi - Agaricus spp., Marasmius oreades): Fairy rings grow 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 (photo). Areas previously covered with trees or fill which contained stumps or logs are prime candidates for development of fairy rings. Fairy rings are a common problem on newly established golf greens that contain a high level of organic matter. Fairy rings 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. Fairy rings are difficult to control with fungicides since soil in the infected area is almost impervious to water. Sporadic success has achieved by aerating and drenching with fungicide.

Gray Leaf Spot

(fungus - Pyricularia grisea): Gray leaf spot develops rapidly with abundant moisture and warm temperatures on St. Augustinegrass (photo). It is especially troublesome in shaded areas that remain damp for some time. Under these conditions, the disease causes serious thinning of the turf. Leaf spots first appear as tiny brown to ash- colored spots with purple to brown margins that enlarge and become diamond-shaped. In severe cases, lesions develop on stems and spikes and the leaves wither and die. Turfgrass may have a burned or scorched appearance resulting from death or spotting of the leaf blades.

Management: Avoid application of soluble nitrogen fertilizers on moderately shaded lawns during summer months. Apply water early in the morning only when water is needed. Avoid evening waterings which keep the leaf surface wet for long periods. Catch and remove grass clippings where gray leaf spot is a problem. Several fungicides are recommended for gray leaf spot control.

Necrotic Ring Spot

(fungus - Leptospheria korrae): Circular patches over a foot in diameter appear in the spring, fade with warmer temperatures and then reappear with heat and drought stress (photo). 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.

Nematodes

(nematodes - many species): Affected areas appear yellow and thin, and do not respond to watering or fertilizing (photo). Nematodes feed on turfgrass roots which prevents absorption of water and nutrients. Roots may be stunted, swollen or blackened. Symptoms often are more apparent in hot dry weather because damaged roots cannot take up water fast enough to replace that lost by transpiration. Damage may be more severe in sandy soils.

Management: Care to avoid the introduction of nematodes into the area is the best prevention. Clean all equipment thoroughly. Adequate and properly timed watering reduces the damage caused by nematodes. The effectiveness of fumigant and nonfumigant nematicides depends on the type and texture of the soil. They are most effective on light sandy soils and least effective in heavy clay soils. Heavy watering following the application of nonfumigants is necessary to move the chemical to the root zone.

For additional information Refer to general section on nematodes and root knot nematode

Pink Snow Mold

(fungus - Microdochium nivale): 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

(fungi - Erysiphe spp.): 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

(fungus - Pythium aphanidermatum): 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 (photo). 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.

Rust

(fungus - Puccinia cynodontis): 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 (photo). 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.

Seedling Disease

(fungi - Pythium spp. and Rhizoctonia spp.): Seedling blight kills the young plants either before or just after emergence, resulting in a reduced stand. Post-emergence attacks cause the seedlings to collapse and die soon after emergence. Seedling diseases are especially damaging during periods of adverse conditions, such as cool, wet weather. Improper planting such as covering the seed too deeply, also increases seedling blight.

Slime Mold

(fungi - Physarum spp. and Fuligo spp.): Dark gray-to-black crust-like material will form on the leaves and stems of turfgrass. The soot-type material rubs off easily on shoes and clothing. Slime Mold fungi feed on decaying organic matter splashed upon the leaves and stems. They do not feed on green grass and cause no damage other than shading. Slime molds can be removed from the grass by applying water under pressure with a water hose, mowing, or by brushing with a broom. No chemicals are necessary.

Smut

(fungus - Ustilago cynodonis): Smut galls replace seed in the spike (photo). The inflorescence (flower) is often distorted. Since the fungus causes a systemic infection, fungicides are not effective. Control by close mowing and proper fertilization, which keeps the grass in a vegetative growing condition, preventing seed head development.

Spring Dead Spot

(Disease complex (fungi) - Leptosphaeria korrae, Gaeumannomyces graminis var. graminis, Ophiosphaerella herpotricha): When turf begins regrowth in early spring, well-defined circular dead spots become evident (photo). Individual spots may range in size from a few inches to several feet in diameter and are usually depressed. Margins of affected areas are usually even, but may become irregular when individual spots grow together to form large areas. Leaves of affected turfgrass are a bleached straw color, while stolons and roots are black and rotted. Spring Dead Spot is a crown, root and stolon rot of dormant grass. Turf recovers very slowly during the summer from stolons creeping in from the border of affected areas. Disease develops again the following year in the same areas and spots enlarge each year.

Management: Fungicide applications must begin in late summer or early fall when the fungus is thought to be most active. Judicious use of nitrogen fertilizer helps to reduce disease severity. Ammonium-based nitrogen fertilizer combined with potassium reduce spring dead spot over time.

Summer Patch

(fungus - Magnaporthe poae): Initially, summer patch resembles dollar spot but patches quickly grow and affect large areas of turf. Affected areas may appear dark green initially and then reddish-brown to bronze colored. As leaves die, turf becomes straw-colored in irregular patches, six inches to several feet in diameter. Occasionally, a frog-eye appearance is observed where turf is green in the middle of the patch. Summer patch is more severe on heat-stressed areas such as sunny, exposed slopes and areas adjacent to sidewalks and driveways. Environmental factors important to disease development are moist soils and root zone temperatures exceeding 75 ^oF.

Management: It is essential to have adequate nitrogen levels. Slow release forms of nitrogen have been shown to be more effective. DMI fungicides (triadimefon, fenarimol, propiconazole) are effective as preventive applications while thiophanate methyl soil drenches show some curative activity. Fungicides are ineffective if turf is allowed to enter drought-induced dormancy.

St. Augustine Decline, Centipede Mosaic

(virus - SAD): In early infection stages, leaves show a chlorotic (yellow) mottling (photo). The mottling or mosaic symptom becomes progressively more severe until a chlorotic appearance is observed. In later stages of disease development, leaves and stolons begin to die and invading grasses and weeds crowd out weakened St. Augustine or Centipede grass. Infected grass does poorly in shaded areas.

Management: Plant a resistant variety - Floratam, Raleigh or Seville. Seville is very susceptible to downy mildew. Floratam is susceptible to cold injury and should not be used in more northern areas. Raleigh is adapted to the same areas as common St. Augustinegrass. No chemicals are available to treat diseases caused by viruses.

Take-all Patch, Bermuda Decline, Take-all Root Rot

(fungi - Gaeumannomyces graminis var. graminis or avenae (photo)): Take-all root rot fungus is active in fall and winter when there is abundant moisture and moderate temperatures. However, symptoms are often expressed in late spring or early summer when affected turfgrass first experiences the stressful effects of high temperature and dry weather (photo). This disease has the ability to destroy large sections of turfgrass if left uncontrolled.

The first symptom is often yellowing of the leaves which eventually die. Turf becomes thin as roots, nodes and stolons become infected and plants die. Unlike brown patch, leaves of take-all infected plants do not easily separate from the plant when pulled. Roots become rotted so damaged stolons are easily pulled from the ground, similar to white grub damage. Regrowth of grass into affected areas is often slow and unsuccessful.

Management: Controlling take-all is not easy and both cultural and chemical methods should be considered. Good surface and subsurface drainage is important. Irrigate only when required, and infrequent but thorough water is preferred to frequent shallow watering. Verticutting to remove thatch also helps. Aerification alleviates soil compactions and promotes a deeper, more vigorous root system. Balanced fertility is important. If possible, adjust the soil pH in the upper root zone to a range of pH 6.0 to 6.5. Preventive fungicides are best applied in the fall since the fungus is thought to be most active at that time.

PHYSIOLOGICAL PROBLEMS OF TURF

Soil Compaction-: Certain soils are compacted easily, especially in areas of heavy foot traffic. This condition prevents adequate gas exchange, penetration of moisture and nutrients, and restricts root growth. Aerification corrects this condition.
Dog Urine Injury-: Circular spots 8 to 10 inches in diameter may appear in areas frequented by female dogs. Heavy watering helps dilute the salt concentration and corrects this condition.
Fertilizer Burn-: Commercial fertilizers are salts and can burn turfgrass when applied excessively. This condition is most often seen where fertilizers are spilled.
Excessive Shading-: Most lawn grasses require full sunlight. When a lawn is fertilized, this in turn stimulates growth of shrubs and tress that shade turfgrass. Selective pruning of trees and shrubs helps correct this condition. St. Augustinegrass and tall fescue are somewhat more shade tolerant than other turf types.
Sun Scald-: Clipping grass too closely removes foliage necessary for food manufacturing and exposes stolons to direct sun rays. When this occurs, a brown lesion or burned areas is found on the upper surface of the stolon. Avoid mowing too closely.
Improper Fertilization-: Excessive use of an individual element, such as nitrogen, makes plants more susceptible to disease attack. Avoid this problem by fertilizing according to soil test recommendations.
Shock-: Allowing grass to become too tall before mowing causes grass to experience shock and lose vigor. Mow frequently to prevent this condition.
Permanent Wilt-: Grass allowed to become too dry may pass the permanent wilt stage where recovery is not possible. This may occur where water does not penetrate because of compaction.