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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

Symptoms:

  • 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:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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

Symptoms:

  • 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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