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identify lawn diseases

We help customers treat a number of common Minnesota lawn diseases.
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Common Minnesota Lawn Diseases

Brown Patch

brown patch lawn disease


  • Rings or patches of blighted turfgrass that measure 5 inches to more than 10 feet in diameter.
  • Leaf spots and "smoke rings" - thin, brown borders around the diseased patches that appear most frequently in the early morning.

Conditions Favoring Disease:

  • Active at cool temperatures on warm-season grasses in the spring and fall (over85F during the day and over 60 F at night).
  • Occurs in areas that experience extended periods of wetness.

Fairy Ring

fairy ring lawn disease


  • Symptoms vary with causal agents.
  • Aboveground mushroom and puff ball basidiocarps may or may not occur.
  • Typically has outer rings that are either dark-green or brown in color.
  • Shape and size of rings vary depending on the species.
  • Activity in turf ceases when the individual rings come in contact with each other.
  • Some causal agents form fruiting bodies, but not rings and vice versa.

Conditions Favoring Disease:

  • Typically occurs in the summer.
  • Can also occur on cool-season turfgrass in mild winter climates

Gray Snow Mold

gray snow mold


  • Evident after snow melts.
  • Light brown, gray, or strawcolored patches 10 inches in diameter.
  • Patches can increase to several feet and coalesce
  • Rust-, brown-, or black-colored sclerotia also appear on the infected leaves.

Conditions Favoring Disease:

  • Snow cover, especially snow that lasts more than 90 days.

Leaf Spot/Melting-Out

leaf spot / melting out lawn disease


  • Purplish-brown to black spots with tan centers on the leaf blade and sheath.
  • Lower leaves of infected plants become shriveled and blighted.
  • In severe cases, almost all of the leaves and tillers die.
  • Typically follows the appearance of leaf spots on cool-weather turfgrass.

Conditions Favoring Disease:

  • Temperatures between 40°F and 80°F.
  • Areas with 10 hours a day of foliar wetness for several consecutive days.
  • High amounts of nitrogen and a low mowing height.

Dollar Spot

dollar spot


  • Sunken, circular patches that measure several inches
  • Patches turn from brown to straw color and may eventually coalesce, forming irregularly shaped areas.
  • May display small lesions that turn from yellow-green to straw color with a reddishbrown border.
  • Lesions can extend the full width of the leaf.

Conditions Favoring Disease:

  • Continuous high humidity at temperatures between 59°F to 86°F.
  • Favored by warm days, cool nights, and intense dews.
  • Infects areas with low levels of nitrogen.
  • More severe in dry soils.

Fusarium Patch

fusarium patch


  • Yellow or reddish-brown patches 1 inch to 6 inches in diameter
  • Periphery of patches are reddish-brown or pink in color.
  • “Smoke rings”—thin, brown borders around the diseased patches that appear only in the early morning—can occur.

Conditions Favoring Disease:

  • Thrives in temperatures less than 60°F in wet conditions.
  • Infects areas with slow growing conditions and heavy thatch.
  • Microdochium nivale is termed Fusarium patch when it occurs in the absence of snow cover.

Large Patch

large patch


  • Rings or patches of blighted turfgrass that measure up to 10 feet in diameter.
  • Leaf spots, blighted rings and patches and “smoke rings”—thin, brown borders around the diseased patches that appear most frequently in the
    early morning.
  • Blackened or rotted sheaths and stolons of turfgrass near the soil layer.

Conditions Favoring Disease:

  • Active at cool temperatures on warm-season grasses in the spring and fall (77° to 83°F canopy temperatures).
  • Occurs in areas that experience extended periods of wetness or low areas subjected to standing water.

Pink Snow Mold
(Microdochium Patch)

pink snow mold


  • Yellow, tan, or salmon-colored water-soaked patches that measure 1 to 8 inches or more in diameter.
  • Pale pink around the edges.
  • Spores are produced in white or salmon-colored sporodochia that are found on the dead tissue.
  • Blighting can occur in streaks from spores tracking on the equipment wheels.

Conditions Favoring Disease:

  • Favors temperatures of less than 60°F.
  • More severe where snow has fallen on unfrozen soil or in cold, rainy weather.
  • Microdochium nivale is commonly called Fusarium patch in the absence of snow cover—but the causal organism is the same.

Necrotic Ring Spot

necrotic ring spot


  • First appears as thinned yellow to light-green circular patches that are 3 to 15 inches in diameter.
  • Can expand up to 3 feet in diameter.
  • Eventually turn brown or straw-colored and die.
  • Roots and rhizomes of the affected turfgrass turn brown to black.
  • “Frog-eye”—a symptom where less susceptible grass species survive inside the diseased patch—can also occur.

Conditions Favoring Disease:

  • Initiates in moist soil.
  • More severe in higher temperatures (of up to 80°F) and drought conditions.
  • Seeded sites, as well as sodded sites in newly cleared woodlands, are susceptible.
  • Found in areas with compacted soil and that are high in nitrogen during the spring and summer.

Pythium Blight

pythium blight


  • Appears suddenly during hot, humid weather.
  • Greasy, brown circular spots that are initially about 3/4 inch to 2 inches in diameter.
  • Rapidly enlarges in size
  • Water-soaked and dark-colored early in the morning.
  • Forms fluffy white masses of fungal mycelium (cottony blight) and can coalesce to form large, irregular areas of dead turf.
  • Infected patches may appear bronzish-orange in color.

Conditions Favoring Disease:

  • Found in areas with poor drainage and air circulation as well as in locations that are high in salinity or nitrogen.
  • Favors night temperatures of over 68°F.
  • Occurs in areas that experience more than 10 hours a day of foliar wetness for several consecutive days.

Rusts: Crown, Leaf, Stem, Stripe

lawn rusts


  • Light yellow flecks initially on the leaf blades and sheaths.
  • Flecks enlarge, elongate, and turn yellow in color.
  • Infected areas rise above the epidermis and then rupture, releasing spores that are yellowish-orange to reddishbrown in color.
  • Leaf blades turn yellow, starting at the tip and progressing to the base sheath.
  • Severe disease infection can cause the shoot to turn yellowish to reddish-brown in color and slow in growth.
  • Turf may appear thin as individual shoots die.

Conditions Favoring Disease:

  • Typically occur in early spring through fall, depending on the location of the turf.
  • Favors low-light areas.
  • Depending on the species, rusts favor temperatures between 65°F and 86°F.
  • Severe rust infections occur on slow-growing turfgrass, particularly those with low nitrogen levels and/or plant water stress.

Powdery Mildew

powdery mildew


  • First appears on the leaves as individual tufts of fine, white mycelium.
  • The tufts enlarge and coalesce, causing the leaves to have a grayish-white or powdery appearance.
  • Severely infected turf turns yellow, then tan and brown in color.
  • Stressed turf that is severely infected can die.
  • Severely infected turf, especially in shaded areas, can become thinned.

Conditions Favoring Disease:

  • Favored by humid, cloudy weather with temperatures between 60°F and 72°F.
  • Occurs in areas under stress.
  • Low light and high humidity
  • Common in areas with poor air circulation, but does not require a film of water to infect turf.

Red Thread and Pink Patch

red thread and pink patch


  • Patches that are reddish-brown in color and 1 to 4 inches in diameter up to 2 feet.
  • Causes a gelatinous mass of pink mycelium with watersoaked leaves.

Conditions Favoring Disease:

  • Temperatures between 40°F to 85°F and in locations that are low in nitrogen.
  • Areas that experience more than 10 hours a day of foliar wetness for several consecutive days
  • Pink patch usually develops in the presence of red thread.
  • The two diseases often occur under the same conditions and at the same times.

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"Jared's Lawn Care does excellent work! They are always there on-time and on the day they said they would be. They are very polite when I call for any questions and go out of their way to answer and accommodate my lawn care needs. Sometimes even surprised my expectations!! Jared is always polite and has a nice, comfortable way about him and is easy to talk to. But when it came down to business he gets the job done quickly. Cleanliness is 100% and I am always proud of my lawn and excited when I come home from work and it is done. A sigh of relief and I enjoy it. Thanks guys. I love you for making my life so much easier!”
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Kevin Y., Brainerd, MN
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our property...it is so wonderful!!  We have never seen our property look so great!!  We could not believe the pictures that Jared sent us after all the cleaning out that he did.....fantastic!!!!
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Kurt, H., Baxter, MN