Common Lawn Diseases

Learn about how to control the most common lawn diseases.

Lawn Diseases: Anthracnose

Reddish-brown spots on leaves • blighted areas of lawn can vary in size from 2 inches to 10 feet.

Favorable Conditions1

Warm to hot weather (75 to 95 degrees) • high humidity • excess rain. Over-fertilizing and heavy thatch also encourage disease.

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Lawn Diseases: Brown Patch

Leaves and stems die out in large, circular patches in lawn • one of the most common fungus diseases of fescue lawns.

Favorable Conditions1

Warm to hot weather (75 to 95 degrees) • high humidity • excess rain. Overfertilizing and heavy thatch also encourage disease.

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Lawn Diseases: Copper Spot2

Grass blades develop small red spots that enlarge and become darker red • grass is infested in small, circular patches 1 to 3 inches wide • grass within the spots dies • can look like Dollar Spot.

Favorable Conditions1

Mild to warm temperatures (70 to 80 degrees); high humidity. Over-fertilizing and heavy thatch also encourage disease.

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Lawn Diseases: Dollar Spot

Grass dies in small, circular spots 4 to 12 inches wide • spots may fuse together in big blotches.

Favorable Conditions1

Mild to warm weather (60 to 85 degrees) • excess moisture • under-fertilization. Over-fertilizing and heavy thatch also encourage disease.

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Lawn Diseases: Powdery Mildew2

White to light gray moldy-looking growth on grass blades

Favorable Conditions1

Mild temperatures (65 degrees) • damp weather and excess moisture • shady areas. Overfertilizing and heavy thatch also encourage disease.

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Lawn Diseases: Red Thread

Tan to bleached-looking grass blades that shrivel from the tips • small patches of dead grass • in wet weather you may see small pink thread in the grass.

Favorable Conditions1

Mild temperatures (60 to 75 degrees) • high humidity • misty weather • under-fertilization. Over-fertilizing and heavy thatch also encourage disease.

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Lawn Diseases: Rust

Dust-like orange-colored spores cover grass blades • affected areas of lawn have a rusty look • doesn't usually hurt the grass, but is a nuisance.

Favorable Conditions1

Mild temperatures (60 to 75 degrees) • dry weather or conditions that favor the slow growth of grass. Overfertilizing and heavy thatch also encourage disease.

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Lawn Diseases: Stripe Smut2

Grass blades turn pale green and are stunted • spores form long black stripes on grass blades • grass blades curl and die.

Favorable Conditions1

Cool temperatures (50 to 60 degrees) • excess moisture. Over-fertilizing and heavy thatch also encourage disease.

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Lawn Diseases: Summer Patch, a.k.a Frog Disease

Grass forms light green patches up to 24 inches wide that later turn a reddish brown • some patches may have circle of green grass in center

Favorable Conditions1

Warm temperatures (80 to 95 degrees) • high humidity • drought-stressed grass Overfertilizing and heavy thatch also encourage disease.

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1. Overfertilizing and heavy thatch also encourage disease.

2. Reprinted with permission from the American Phytopathological Society, St. Paul, MN.

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