Identify Specific Fungal Disease

Using the symptom description in the left hand colun try to identify the disease that is attacking your lawn. Then click on the name of the disease for more details about the symptoms and recommendations for possible solultions.

Disease by Symptoms
SymptomProbable Fungal Disease
Brown or Tan Rings with Green CentersFusarium blight
White or Tan Cobwebby SpotsDollar spot
Patches Surrounded by “Smoke Rings”Brown patch
Blackened Wet PatchesPythium blight
Fine Threads on Grass BladesRed thread
Gray or Pink Patches after Snow MeltSnow mold
Lush Growth Surrounded by Dead ZoneFairy ring
Pale; Distorted Grass BladesLeaf smut
Purplish Black Spots on BladesLeaf spot
Brown Rings Appearing SuddenlyNecrotic ring spot
White or Gray Fuzz on GrassPowdery mildew
Orange or Brown Pustules on GrassRust
Small Gray or Yellow Blobs on GrassSlime molds
Mushrooms Emerge Through TurfBuried wood

Fusarium Blight

Brown or Tan Rings with Green Centers Indicate Fusarium Blight
Reddish-brown circular spots in the lawn 2 to 6 inches in diameter indicate Fusarium blight (Fusarium tricinctum). Eventually the spots turn tan, then yellow, and increase in size until they grow together. Healthy turf may grow in the center of each infected circle, giving it a characteristic “frog’s-eye” look. Roots and crowns of grass plants are rotted.
Fusarium blight chiefly affects Kentucky bluegrasses and can ruin an entire lawn. It occurs as temperatures approach 90° F in sunny areas, often beginning near a walkway or driveway. If the weather remains unusually warm and dry, it may persist through the summer. Fusarium is common in lawns with thick thatch, and/or that have been improperly watered and fertilized.
Control Fusarium by mowing the grass high (3 inches tall in hot weather) and bagging and discarding the clippings. Dethatch and fertilize only in the fall or very early spring. Because drought encourages Fusarium, proper deep watering will help control it. Eventually, lower temperatures and increased precipitation deactivate the disease, so infected lawns usually recover in the fall. At that time you may have to overseed a severely damaged lawn. Look for a seed variety with resistance to Fusarium blight.

Dollar Spot

White or Tan Cobwebby Spots Caused by Dollar Spot
Symptoms of dollar spot (Sclerotinia homeocarpa) resemble those of Fusarium blight. This fungus appears as tan or straw-colored spots the size of silver dollars. It thrives on dry, undernourished lawns, attacking all grasses except centipedegrass, St. Augustine grass, and tall fescue. Small, white, cobwebby spots appear in the morning and turn brown later in the day. Infected areas may increase in number but they rarely grow together. Dollar spot is most likely to occur in moderate temperatures (60° to 90°F) where there is heavy thatch. Lawns that are underfertilized and growing in acidic soils are prone to attack. High humidity within the turf activates this fungus.
Spray a general garden fungicide containing sulfur on infected areas every 3 to 5 days until symptoms disappear. Spray the grass with a quick-acting liquid lawn fertilizer twice, about 2 weeks apart, to boost nitrogen levels and help the grass fight off the dollar spot. Water the lawn deeply every week during dry spells. Also, recent studies show that spraying a diluted plant tonic containing seaweed extracts on the grass once a month helps control this fungus. When mowing infected grass, bag and dispose of clippings in the trash to avoid spreading the disease. To help avoid the problem next year spread granular lime in the fall if your lawn soil is too acidic.

Brown Patch

Discolored Patches Surrounded by Smoke Rings Suggest Brown Patch
Also called summer patch, brown patch fungus (Rhizoctonia solani) kills oval to circular areas of grass up to 2 feet in diameter. All grass species are vulnerable. Infected areas turn from purplish green to brown. A “smoke ring” of grayish-black fungal threads is often visible fringing the infected patch. Inside the patch, the grass dies and stays upright. A few plants of green grass may remain. A severe attack kills all the grass and leaves bare patches. This disease may strike virtually overnight if conditions are right--hot humid weather and temperatures of 75° to 95°F. Other risk factors include excess nitrogen fertilizer, thatch buildup, and poor drainage.
For immediate treatment, spray a general garden fungicide containing sulfur on the infected and adjacent areas according to label instructions for turf. An important long-term treatment is to remove thatch with a dethatching rake and dispose of it in the trash. Avoid overfeeding the lawn with nitrogen fertilizer, especially in the summer. If soil needs improved drainage, aerate and topdress the lawn with organic matter. Avoid late afternoon watering during hot weather. Improve poor air circulation by thinning nearby tree or shrub branches.

Pythium Blight

Blackened Wet Patches Caused by Pythium Blight
Also known as cottony blight, grease spot, and damping-off, Pythium fungus disease is especially likely to appear in new lawns that have been seeded too densely. It is a serious pest of annual and perennial ryegrass and Kentucky bluegrass. Symptoms are blackened, watersoaked patches of flattened grass blades 2 to 6 inches in diameter enlarging to 2 feet across. In humidity, the diseased areas may also develop visible cottony fuzz. Grass usually dies in 24 hours, and new grass does not grow in denuded areas.
Pythium blight is often spread by water, so infected areas may appear as streaks indicating the direction of runoff. Do not walk through infected turf, as this spreads the fungal spores. Hot, humid weather encourages this disease, but cool, dry weather stops it, so it’s a good idea to delay any seeding until fall if possible. Control by mowing higher, correcting drainage problems, and removing excessive thatch. Avoid watering the lawn in the evening during hot, humid weather.

Red Thread

Fine Threads on Grass Blades Caused by Red Thread
Circular or irregular patches of scorched grass and fine red or rusty threads sticking up from diseased grass blades and stretching from leaf to leaf indicates red thread (Laetisaria [Corticium] fuciforme). Pink, gelatinous masses indicate the presence of pink patch (Limonomyces roseipellis). These fungi are related and occur most often in the Northeast and the Pacific Northwest, in their cool, damp conditions and moderate temperatures (67° to 75°F). Red thread occurs primarily on perennial ryegrasses and fine fescues and somewhat less on Kentucky bluegrasses. It occasionally attacks Bermudagrass and Zoysia grass in the South. Red thread does not spread by spores, but by bits of infected tissue (and “threads”) that are spread around by mowing.
Turf that is nitrogen deficient is often prone to infection by red thread. Spray infected grass with a quick-acting liquid lawn fertilizer to stimulate growth. Mow to cut off infected blade tips, but be sure to bag the clippings and dispose of them in the trash.

Snow Mold

Gray or Pink Patches after Snow Melt Indicate Snow Mold
Snow mold is a collective term for fungal diseases that infect grass under snow cover. Two different fungi cause this problem. Gray snow mold, or Typhula blight (Typhula sp.) is most common on lawns that have been covered by heavy snow throughout the winter. When the snow finally melts in spring, it reveals patches up to 2 feet across covered with white or gray fungus. Another culprit, Fusarium patch, produces white or pink dead patches of matted grass 12 or more inches across. Fusarium patch may occur even if it doesn’t snow, but patches will be only 1 to 2 inches across. They change from purple to tan to white and may develop pink mold. Both diseases thrive in cool to cold, wet weather from late fall to early spring when temperatures are 28° to 45°F. Often they occur where snow is packed down by foot traffic.
To repair damaged areas, loosen up matted grass to improve air circulation, and spray a general garden fungicide containing sulfur according to label instructions for turf. Aerate the soil and improve drainage if needed. Avoid overfeeding with nitrogen fertilizer in the fall, and remove thatch if it is more than ¼ inch thick. Avoid walking on the lawn during the winter, especially if there is snow cover.

Fairy Ring

Lush Growth Surrounded by a Dead Zone Indicates Fairy Ring Fungi
Bright-green circular areas in the lawn growing more rapidly than the rest the turf suggests that the grass is infected with one or more species of fairy ring fungi, chiefly Marasmius oreades. This lawn disease attacks all grass species. Fairy ring fungi grow in decaying organic matter, such as old tree roots, just below the soil surface. This releases extra nitrogen into the soil, which accounts for the luxuriant grass growth in the rings. The zone of overstimulated growth may be 4 to 12 inches wide, but the ring itself may reach 50 feet across. Eventually the overgrown patches of grass decline, and a circle of mushrooms often develops around the infected area.
The disease typically develops during moist warm spells in spring and fall. Sometimes it develops after a sprinkler system has been installed in the yard. To control fairy rings, try liming the lawn with granular lime to reduce soil acidity. Mow closer than usual (about 1-1/2 inches or so) and collect then discard the clippings. Drench the soil in the ringed areas with copper sulfate or iron sulfate according to label instruction to kill the fungus. More drastic action involves digging out the infected areas of the lawn to a depth of 2 feet and extending 1 foot beyond the diseased patches in all directions, then filling in with new soil and reseeding those areas.

Leaf Smut

Pale, Distorted Grass Blades Caused by Leaf Smut
A pale green cast and stunted growth of grass blades are signs of leaf smut, also called stripe smut (Ustilago sp. and Urocystis sp.). On individual blades, narrow gray or black stripes develop, which rupture and release masses of spores. The infected blades curl, tear easily and look shredded. If you drag a white cloth across the infected grass, it will be discolored by the black spores. Leaf smuts primarily attack Merion Kentucky bluegrasses and thrive in cool, moderate to moist conditions in spring and fall.
Control leaf smuts by mowing the lawn frequently to cut off the infected blade tips. Collect and discard the clippings. Do not allow the thatch layer to get thicker than ¼ inch.

Leaf Spot

Purplish Black Spots on Blades Caused by Leaf Spot
Reddish-brown to purplish-black spots with pale centers on grass blades are caused by leaf spot fungi (Drechslera[Helminthosporium] sp.). The spots develop on the blades, stems and crowns. Eventually the blades shrivel, crowns and roots rot and die and then irregular patches of thin grass develop in the lawn. The disease is often mistaken for drought injury, so check suspicious grass blades carefully. It is especially likely to occur on common Kentucky bluegrass varieties.
Symptoms occur in early spring and late fall when the weather is cool and moist. Spray affected areas of the lawn with a general garden fungicide containing sulfur as directed on the label until symptoms disappear. Avoid overfeeding with nitrogen fertilizers.

Nectrotic Ring Spot

Sudden Brown Rings Mean Necrotic Ring Spot
Necrotic ring spot, also known as spring dead spot (Leptosphaeria korrae) causes grass, especially Bermudagrass, to look tattered. Roots and runners (stolons) become discolored and rotted. Brown rings develop over the lawn. They usually appear suddenly in grass that very recently seemed perfectly healthy. The disease is promoted by thatch buildup and poor air circulation near the soil.
To control ring spot, remove thatch, mow the grass high and adopt proper watering and feeding practices to reduce stress to the grass. Improve air circulation by pruning nearby shrubs and trees carefully.

Powdery Mildew

White or Gray Fuzz on Grass Means Powdery Mildew
A thin white or grayish powdery coating on grass blades is a sure sign of powdery mildew (Erysiphe graminis). It often occurs in shaded areas when nights are cool and humid, especially on Kentucky bluegrass. Severe infection causes the grass to turn yellow and die.
Control by spraying the infected turf and adjacent areas with a general garden fungicide containing sulfur as directed on the product label until symptoms disappear. All turfgrasses need some sun or bright light to thrive, even those labeled for “shade”. If your grass has chronic mildew problems and you cannot provide more light for it, substitute an evergreen groundcover such as pachysandra, liriope or ivy for grass.
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Orange or Brown Pustules on Grass Means Rust
Rust disease (Puccinia sp.) first appears on grass blades and stems as small orange to reddish-brown powdery pustules. As they mature they turn from brown to black. Heavily infested turf becomes thin with an overall yellow-orange to reddish-brown color. Infected leaves turn yellow, wither and die. Rust usually occurs in late summer in warm, humid conditions. It often develops on grasses that are stressed by drought, low nitrogen, low mowing height, and shade. Bluegrass, ryegrass and Zoysia grass are most commonly affected.
To control rusts, spray infected areas with a general garden fungicide containing sulfur according to instructions on the label until symptoms disappear. Fertilize by spraying turf with a quick-acting liquid lawn fertilizer to stimulate growth, and mow more frequently, making sure to collect and discard the clippings. Adjust mowing height to the type of grass on your lawn. Try overseeding with resistant varieties of Kentucky bluegrass and perennial ryegrass.
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Slime Molds

Small Gray or Yellow Blobs on Grass Mean Slime Molds
Slime mold (Physaricum cinereum) first appears as white, yellow or gray puffy or slimy growths on grass blades, forming powdery puffs as they dry. Usually this growth appears in area of the lawn that is moist, shaded, and has poor air circulation. Fortunately, slime molds do not really harm the grass; they feed on decaying organic matter or thatch. They usually disappear as soon as the weather gets drier. However, if the growth is abundant, it may suffocate grass plants and cause turf to thin out. Control this fungus by simply sweeping it off the grass with a broom or washing it off with a garden hose.

Mushrooms In Grass

Mushrooms Emerge in Turf Due to Buried Wood
A crop of mushrooms in the lawn usually means that something is decaying under the lawn’s surface. An old stump or scrap of wood from construction, for example, can be the source of decaying material for many years. If wood chips are incorporated into your topdressing material, you’ll have mushrooms for awhile.
There is no way to eliminate mushrooms from turf. However, they do not damage the grass, and they are easily removed by handpicking them or mowing them over. They often pop up after a spell of damp weather, but wither as soon as the soil dries out. Eventually the woody subsoil material decomposes completely and the mushrooms go away. NOTE: None of the mushrooms that grow in lawns are edible.