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When the snow finally melts, and warmer weather arrives in Minnesota, we all want a lawn that looks great and lets us enjoy time outside! Lawn diseases can be a real challenge for many homeowners. Fungal infections like dollar spot, red thread, and snow mold can damage grass, leaving unsightly patches and weakening your lawn's health. These diseases may thrive under conditions such as poor drainage, overwatering, or compacted soil. We'll help you identify and prevent these issues to maintain a lush, green lawn throughout the growing season.
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Below are some of the common lawn diseases we see here in Minnesota. Need help identifying and addressing your lawn issues? Contact us or give us a call at 763-682-5134 - we're happy to help!
Brown Patch
Symptoms:
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Rings or patches of blighted turfgrass that measure 5" - 10' in diameter
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Leaf spots and "smoke rings" - thin, brown borders around patches that appear most frequently in the morning.
Conditions Favoring Disease:
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Active at cool temperatures on warm-season grasses in the spring and fall (over 85°F during the day and over 60°F at night).
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Occurs in wet areas.
Dollar Spot
Symptoms:
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Sunken, circular patches that measure several inches
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Patches turn from brown to straw color; may coalesce, forming irregularly shaped areas
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May display small lesions that turn from yellow-green to straw color with a reddish-brown border; can extend the full width of the leaf.
Conditions Favoring Disease:
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Active at cool temperatures on warm-season grasses in the spring and fall (over 85°F during the day and over 60°F at night).
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Occurs in wet areas.
Fairy Ring
Symptoms:
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Symptoms vary with casual agents
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Mushroom and puff ball may occur
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Typically has outer rings that are dark-green or brown; shape and size may vary
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Activity stops when rings touch each other
Conditions Favoring Disease:
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Typically occurs in the summer
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Can also occur on cool-season turfgrass in mild winter climates
Fusarium Patch
Symptoms:
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Yellow or reddish-brown patches 1" - 6" in diameter
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Edge of patches are reddish-brown or pink
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"Smoke rings" - thin, brown borders around the diseased patches can occur in early morning
Conditions Favoring Disease:
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Thrives in temperatures less than 60°F in wet conditions
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Infects areas with slow growing conditions and heavy thatch
Gray Snow Mold
Symptoms:
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Evident after snow melts
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Light brown, gray, or straw colored patches 10" in diameter; can increase to several feet & converge
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Rust, brown, or black-colored sclerotia appear on infected leaves
Conditions Favoring Disease:
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Snow cover, especially snow that lasts more than 90 days
Pink Snow Mold
Symptoms:
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Yellow, tan, or salmon-colored water-soaked patches measuring 1" - 8"+ in diameter
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Pale pink around the edges
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Spores are produced in white or salmon-colored sporodochia found on dead tissue
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Blighting can occur in streaks from spores tracking on equipment wheels
Conditions Favoring Disease:
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Favors temps of less than 60°F; more severe where snow has fallen on unfrozen soil or in cold, rainy weather
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Commonly called Fusarium patch in the absence of snow cover; causal organism is the same.
Necrotic Ring Spot
Symptoms:
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First appears as thinned yellow to light-green circular patches, 3 - 15" in diameter; can expand up to 3'.
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Eventually turn brown or straw-colored and die.
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Roots and rhizomes of the affected turfgrass turn brown to black.
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"Frog-eye" - where less susceptible grass species survive inside patch.
Conditions Favoring Disease:
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Initiates in moist soil; more severe in higher temps (up to 80°F) & drought conditions
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Seeded sites, as well as sodded sites in newly cleared woodlands, are susceptible.
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Found in areas with compacted soil that are high in nitrogen during spring and summer.
Powdery Mildew
Symptoms:
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First appears on the leaves as individual tufts of fine, white mycelium
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Tufts enlarge & combine, causing leaves to have grayish-white or powdery appearance
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Severely infected turf turns yellow, then tan/brown color.
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Stressed, severely infected turf may die or become thinned.
Conditions Favoring Disease:
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Favored by humid, cloudy weather with temps between 60° to 72°F.
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Occurs in areas under stress, with low light and high humidity, poor air circulation (but doesn't require a film of water to infect turf).
Pythium Blight
Symptoms:
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Appears suddenly during hot, humid weather
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Greasy brown circular spots initially 3/4" to 2" in diameter; grows rapidly.
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Water-soaked and dark-colored early in the morning.
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Fluffy, white masses of fungal mycelium (cottony blight) and can combine to form large, irregular patches of dead turf
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Infected patches may appear bronzish-orange in color
Conditions Favoring Disease:
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Found in areas with poor drainage and air circulation, as well as high in salinity or nitrogen.
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Favors night conditions with temps above 68°F.
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Areas that experience 10+ hours a day of foliar wetness for several days
Red Thread & Pink Patch
Symptoms:
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Patches that are reddish-brown and 1" to 4" in diameter, up to 2'.
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Causes a gelatinous mass of pink mycelium with water-soaked leaves
Conditions Favoring Disease:
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Temps between 40° to 85°F and in locations low in nitrogen
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Areas that experience 10+ hours / day of foliar wetness for several days
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Pink patch usually develops in the presence of red thread
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The two diseases may occur under the same conditions at the same time
Rusts: Crown, Leaf, Stem & Stripe
Symptoms:
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Light yellow flecks initially on the leaf blades & sheaths; flecks enlarge and turn yellow.
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Infected areas rise above the epidermis and then rupture, releasing yellow/orange, reddish/brown spores
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Leaf blades turn yellow, tip to base
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Severe disease can cause the shoot to turn yellow to reddish-brown in color and slow growth; turf may appear thin and die.
Conditions Favoring Disease:
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Early spring through fall depending on location
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Favors low-light areas
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Depending on species, favors temps between 65°F and 86°F.
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Severe rust infections occur on slow-growing turfgrass, particularly those with low nitrogen levels and/or water stress.
Ascochyta Leaf Blight
Symptoms:
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Large, irregular patches turn straw-brown in color; appear dead.
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Looks similar to drought stress but appears quickly or overnight
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Infected leaves show a bleached tip, fading with a pinched look between healthy and infected areas
Conditions Favoring Disease:
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Prefers wet and humid weather
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Thick thatch, poor soil quality, over/under fertilizing, and dull mower blades may contribute to the severity of the disease
Photo credit: JayDee Gunnell, Utah State University Extension