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The symptoms associated with this disease will vary greatly depending on the turfgrass species and cultivar, environmental conditions, cultural practices, and strain of _______. Symptoms appearing on cool-season turfgrasses will be quite different from those on warmseason turf.
Brown Patch or Rhizoctonia Blight (Rhozoctonia solani)
On close-cut, cool-season turfgrasses, the disease will occur as circular or sometimes irregular patches of light brown turf that range in size from a few inches to several feet (a few centimeters to several meters). During warm, humid conditions, a dark, purplish to grayish-black "smoke ring" or border may appear along the edges of the patches. This ring is the result of the grey pathogen mycelium growing out of the infected leaf blades. The ring is most noticeable in the early morning when dew is still on the grass or during periods of high humidity and free moisture. As the turf dries, the ring will disappear. The smoke ring does not always occur, so it should not be relied upon as the sole identifying characteristic. In most cases, the dead, light brown or straw-colored leaves will be replaced by new shoots initiated from the crown, stolons, and rhizomes.
Brown Patch or Rhizoctonia Blight (Rhizoctonia solani)
On high-cut, cool-season turf, the disease will appear as a light-browncircular patch that may be up to 2 feet (0.6 m) in diameter. The smoke ring is often not present. The diseased turf will appear sunken or flattened down. Live grass sometimes persists in the centers of the patches, creating a characteristic "frog eye" appearance. Tan, irregular shaped leaf lesions are often apparent on cool-season turfgrasses.
Brown Patch or Rhizoctonia Blight (Rhizoctonia solani)
Brown patch on warm-season turfgrasses, particularly bermudagrass and St. Augustinegrass, has a somewhat different appearance than on coolseason turfs. Warm-season turfs are most susceptible in the spring during spring green-up and in the late fall as the turf enters winter dormancy. The dead patches of leaf tissue may be as large as 15 to 20 feet (4.6 to 6.1 cm) in diameter. Leaf lesions are usually not present. However,plants at the edges of the blighted area will have off-colored shoots. Rather than occurring as a leafblight, the disease affects warm-season turfgrasses more as a shoot and crown rot. Damaged shoots can be easily pulled away from their point of attachment.
Brown Patch or Rhizoctonia Blight (Rhizoctonia solani)
On close-cut turf such as golf greens, _______ appears as bleached spots about the size of silver dollars.
On home lawns or other high-cut turf areas, the turf displays larger bleached patches (1 to 7 inches or 2.5 to7.8 cm wide) that can be so numerous that they overlap or coalesce, forming large irregular areas of damaged turf. Individual leaves on the edge of the dead areas have straw-colored bands or lesions across the blades with reddish-brown borders. In the early morning when dew is on the infected turf, a white, cottony growth of mycelia can be seen on the leaves. As the turf dries, the mycelia disappear. The white mycelium growth may be mistaken for that of Pythium, Nigrospora,or Rhizoctonia.
Lesions begin as small brown to olive-green spots on the leaves and stems. The spots enlarge to oval or circular shapes that are tan to gray with darker borders. The enlarged spots can be seen covered with gray mold or mycelia during periods of warm, wet weather. The leaves of severely infected plants will turn yellow to brown and eventually die. Infected turf areas will have a "burned" or "scorched" appearance similar to that exhibited during drought stress.
Gray Leaf Spot (Pyricularia grisea)
As the snow melts, the symptoms of this disease become apparent as circular areas of light straw-colored to grayish-white turf. The spots range in size from a couple of inches to more than 3 feet (0.9 m) in diameter. The damaged turf is often covered with a grayish-white mold (mycelium) with speckled dark flecks. This mycelium is most apparent on the outer edge of the spots. Although this disease can kill large areas of the turf, in most cases only the leaves are damaged, allowing regrowth from the crown, rhizomes, and stolons.
Gray Snow Mold or Typhula Blight (Typhula incarnata)
Infected turfgrass plants grow more upright and stiff than surrounding healthy plants. This gives the turfgrass area an uneven or clumpy appearance. Infected plants are generally stunted, showing little shoot or root growth. The first symptoms are pale-green or light-yellow blades of grass. As the disease progresses, yellow-green to black streaks run parallel along the blade and leaf sheath. These streaks are actually fruiting bodies containing large numbers of spores. The black spores will rub off as a sooty dust if touched. In the final stages of plant injury, infected blades usually curl, twist, and split between the veins from the tip down. The leaf turns light brown and dies.
Leaf Smuts (Stripe Smut, Ustilago striiformis, and Flag Smut, Urocystis agropyri)
During periods of cool, wet weather, the disease forms circular reddish brown patches ranging in size from less than 1 inch to about 8 inches (less than 2.5 cm to about 20.3 cm) in diameter. As the disease progresses, the patches enlarge and turn light-gray in color. Under very wet conditions, a white to pinkish covering of mycelia can be seen on the foliage of the diseased turf. The mycelia are usually most noticeable on the leading edge of the affected patch.
Pink Snow Mold and Fusarium Patch (microdochium nivale)
The first symptoms appear as small, isolated white patches on the blades. As the disease progresses, the entire blade is covered with white to grayish-white mycelia. At this stage the turf looks like it has been dusted with lime or flour. The advanced stages of the disease will cause the foliage to yellow, then wither, and finally die.
Powdery Mildew (Erysiphe graminis)
The symptoms of _______ are quite variable. In general, only leaves of the plant are infected. During very humid conditions, pink to red mycelia can be seen on the leaves. The red-thread-like hyphae often extend more than 0.25 inch (0.6 em) from the tips and are quite noticeable. Death of the leaf usually occurs from the tip down. Infected turf areas will often have circular or irregular patches of tan dead leaves that range in size from 2 to 6 inches (5.1 to 15.2 em) in diameter. The patches of tan or blighted grass often have a pink to reddish cast because of the red mycelia on the foliage.
Red Thread (Laetisaria fuciformis)
The first symptoms are small yellow spots or flecks on the blades and leaf sheaths. As the infection advances, these spots enlarge until the surface of the leaf splits open and exposes yellow, orange, or dark red pustules. The pustules are filled with powdery spores. Severely infected turf will show thinning and will have a yellowish-brown to orange tint.
Rust (Puccinia spp. and Uromyces spp.)
When the weather is dry and warm, reddish-brown to brown lesions may form on the leaves. The lesions are sometimes surrounded by a yellow halo. As the disease progresses, the centers of the yellow lesions turn black and the yellow halos merge, causing the entire leaf to turn yellow. The yellow leaves eventually turn tan, then brown. The diseased turf usually dies in irregular patterns from a few inches to several yards in size. The diseased areas first appear yellow in color, then change to red-brown, followed by light tan and finally brown as the turf dies. Under close examination with a 20-power hand lens, tiny, grayish-black to black structures (fruiting bodies) can be found on the dying or dead tissue. These small fruiting bodies have black spines projecting from their surface. The root-rot phase of this disease causes lower stems near the crown to turn brown and die. As the disease progresses into the crown, individual stems can be easily pulled from the crown. The entire basal crown area will appear blackened.
Anthracnose (Colletotrichum graminicola and Glomerella graminicola)
In the spring and fall the first symptoms of leaf spots appear as small purplish-black spots on the foliage. As the disease progresses, the spots enlarge in size and become oval in shape with light tan centers. As spots or lesions increase in number and size, the entire blade may wither and die. Crowns, stems, and roots can also be infected. This stage of the disease usually occurs during hot, humid weather. The infected plant part will show a reddish brown rot. The diseased tissue will eventually turn black and die. Severe infection will significantly thin, and in some cases destroy, large areas of the turf stand.
Drechslera Leaf, Crown, and Root Diseases
Leaf spots are tan with a purple to light-brown border and are irregular in shape. These lesions differ from those of Drechslera leaf spot, which are oval with a dark, purplish border. Symptoms first appear at the tips of older leaves, causing the leaf to die from the tip to the base. The symptoms of this disease can appear very similar to those of dollar spot. Crown, root, and shoot rot symptoms appear as black or darkened tissue. The turf turns tan and dies in irregular patterns that range in size from 1 to 14 inches (2.5 to 35.6 cm) in diameter. Greatest damage occurs during hot, dry conditions.
Fusarium Diseases (Leaf Spot, Crown and Root Rot)
The initial symptom ofthis disease is light-green, circular patches that are about 2 to 6 inches (5.1 to 15.2 ern) in diameter. As the disease progresses, patches can be up to 3 feet (0.9 m) in diameter; the turf turns reddish brown and finally light tan as it begins to die. The most characteristic symptom of this disease is the regrowth of the turf in the center of the tan-colored patch, giving it a "frog eye" appearance. Another characteristic symptom is dark brown roots and crown of plants growing along the margins of the patches.
Necrotic Ring Spot (Leptosphaerea korrae)
Early symptoms are dark-colored, circular or irregular spots about 1 to 6 inches (2.5 to 15.2 cm) in diameter. As the disease progresses, the spots may merge, forming large areas of dead turf. In the morning when the turf is wet from dew, or at night when the humidity is high, individual leaves have a slimy or greasy feel and are covered with a purplish-gray to white mycelium. As the leaves dry, the mold disappears, and the leaves wither and die. Some species cause crown and root rot. Infected turf usually appears yellow, thin, and lacking in vigor. Crown and root rot are most common on highly-maintained turf. Both crown and roots will be dark and discolored. Diagnosis by visual observation alone is difficult. Plant material should be sent to a plant disease clinic for positive diagnosis. Infected seedlings can suddenly turn brown in medium to large patches and die. This usually occurs in situations where drainage is poor, causing the soil and plants to stay excessively wet.
Pythium Blight, Cottony Blight, Greasy Spot (Pythium spp.)
This is a very serious disease of bermudagrass. Symptoms include circular patches of bleached, dead turf that occur at the time of spring green-up. The patches range in size from 2 inches to 3 feet (5.1 cm to 0.9 m) in diameter and will increase in size each year, often merging together, giving the appearance of winter injury. After a few years, the centers of the patches may have live turf, causing a "frog eye" appearance. The disease is also characterized by causing severe rotting of the roots and shoots.
Spring Dead Spot (Leptosphaeria narmari)
On bentgrass golf greens, symptoms first appear in the late spring as circular patches of light-brown dead grass. Patches will increase in size from a few inches to about 3 feet in diameter (a few cm to about 0.9 m in diameter), with the most severe symptoms becoming apparent in the summer after heat and drought stress. The centers of the patches often fill in with other grasses (usually annual bluegrass) or weedy species, creating a characteristic "frog eye" appearance. Roots and shoots of the affected turf become dark brown to black in color.
Take All Patch (Gaeumannomyces graminis)
Circular patterns of dark-green, fast-growing turf that occur throughout the growing season. Thin or dead turf is often found inside or outside the circle or rings of dark-green growth. The width of the green band ranges in size from 3 inches to 10 inches (7.6 to 25.4 cm), while the rings may be up to 30 feet (9.1 m) in diameter. The green band is caused by the plants' response to the release of nitrogen during the breakdown of soil organic matter by the fungal organism and by the production of materials that stimulate the turfgrass plant. On occasion, particularly after rainy weather or irrigation, mushrooms or puffballs can be seen growing in the circular band.
Fairy Ring (Many Different Soil-Inhabiting Fungi)
The first symptom of infection is a slight, chlorotic (yellowing) mottling or flecking of the leaf blades. As the disease progresses during its second year, the mottling becomes much worse. By the third year, the turf may be bright yellow and stunted, with a general thinning or death of the turf in irregular patterns. In some cases, the entire turf area may be killed. The initial symptoms of are often confused with iron or nitrogen deficiency. In the case of iron deficiency, leaf chlorosis tends to occur between the veins while the veins themselves stay green. Chlorosis induced by nitrogen deficiency affects the entire blade and produces a general yellowing. As already mentioned, leaf chlorosis has a mottled or flecked appearance (yellow flecks on green). Generally, various weedy grasses and broadleaf weeds will fill in the thin or dead areas. Infected turf is more susceptible to cold and drought stress.
St. Augustinegrass Decline Virus (SADV) (Panicum Mosaic Virus)
Although the appearance on turf may seem threatening to the turf manager, it will not kill or seriously damage the plant. These nonparasitic organisms cause a creamy white, gray to purplish-brown slime on the blades and stems of the turf. This material is actually the fruiting or reproductive structures of the fungi. Irregular patches range in size from 2 inches to 2 feet (5.1 em to 0.6 m) in diameter.
Slime Mold (Mucilago crustacea, Physarum spp. and Fuligo spp.)
Damage usually results in chlorotic, slow-growing, or stunted turf that will eventually thin and, in some cases, die. The symptoms may appear as irregular patches, or the entire turf area may be affected. Symptoms are most severe when the turf is under stress such as high or low temperature, drought, or nutritional deficiencies. Roots may be affected in various ways. Symptoms may include lesions (dark brown or black spots or areas), swelling, or knots. In severe cases the root system may be reduced in size and have an overall light to dark brown to almost black coloration.
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