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Learn to Diagnose and Treat These 8 Lawn Diseases

Joe Churchill

By Joe Churchill

Updated on Jan. 05, 2024

Like people, lawns get sick. It can be minor, like a cold, or more serious. Learn how to identify these diseases so you can treat and defeat them.

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Snow Mold Web on Grass
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Snow Mold

Also known as:

  • Pink Snow Mold (Microdochium nivale)
  • Gray Snow Mold (Typhula incarnata and Typhula ishikariensis)

Where is it found?:

  • Any place where it snows.
  • Other regions where spring weather can be cold and wet.

What causes it?:

  • Cool, wet weather during snow melt.
  • Unfrozen ground.

Brief physical description:

  • White or tan crusted circles that appear matted, like papier maché.
  • Patches can merge into larger areas.
  • Fuzzy-looking mycelia is often present.

Best way to treat or prevent:

  • Do not apply fertilizer late in the fall.
  • Keep grass mowed late into fall.
  • When matting or mycelia appear, carefully rake and remove it.
  • Chemical treatment is rarely needed.

Good to know:

  • In most cases, snow mold lawn disease is cosmetic and will not cause severe lawn damage.
  • It can also reappear in late spring under cool, wet conditions.
  • Kentucky bluegrass, perennial ryegrass and tall fescue are the most susceptible.
  • Snow Mold is a big problem on golf courses and can cause severe damage there.
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Dollar Spot

Also known as:

  • Scerotinia homoeocarpa
  • Clarireedia jacksonii

Where is it found?:

  • Throughout the U.S. in all types of lawn grass.

What causes it?:

  • Not enough nitrogen fertilizer.
  • Excess moisture in the soil and thatch layer.

Brief physical description:

  • Clusters of small white or tan patches ranging from a few inches to a foot in diameter.
  • Spots can coalesce into more prominent areas of discolored grass.
  • Hour-glass lesions on individual leaf blades.

Best way to treat or prevent:

Good to know:

  • As is the case with managing most lawn diseases, maintaining best management practices, such as proper mowing, watering, core aeration and fertility, will go a long way in reducing the occurrence of dollar spot lawn disease.
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Red Thread

Also known as:

  • Laetisaria fuciformis

Where is it found?:

  • Throughout the U.S. in all types of lawn grasses.
  • In shady areas and other areas that remain wet.

What causes it?:

  • Undernourished lawns are susceptible.
  • Over-watering.
  • Poor drainage.
  • Prolonged overcast conditions.

Brief physical description:

  • Areas appear water-soaked.
  • Leaf tip dieback with red, thread-like filaments appearing.
  • Irregular beige patches from a few inches to a few feet in diameter.

Best way to treat or prevent:

  • Collect clippings when the disease is present.
  • Apply a high-nitrogen-source fertilizer at the recommended rate.
  • Disease should disappear in a couple of weeks with adequate fertilizer. If not, you can use a broad-spectrum fungicide like Scotts DiseaseX Lawn Fungicide.

Good to know:

  • Red thread lawn disease often appears in spring and fall during humid, cool conditions.
  • Reseeding with disease-tolerant lawn seed varieties will help.
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Brown Patch

Also known as:

  • Rhizoctonia solani
  • Smoke Ring

Where is it found?:

  • Throughout the U.S. in all types of lawn grasses.
  • Tall fescue and perennial ryegrass lawns are most susceptible.

What causes it?:

  • Hot, humid weather.
  • Excessive fertilizer and water.

Brief physical description:

  • Small to larger light-brown circular patches, most times with a very distinct outer margin.
  • Irregular lesions with a purplish to brown border and tan center may show.

Best way to treat or prevent:

  • Reduce nitrogen fertilizer.
  • Reduce watering frequency and amount.
  • Improve drainage and air circulation.
  • If treatment is necessary, try Scotts DiseaseX Lawn Fungicide or a similar broad-spectrum lawn fungicide.

Good to know:

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Pests and disease cause amount of damage to green lawns, lawn in bad condition and need maintaining
Singjai20/Getty Images

Summer Patch

Also known as:

  • Magnaporthe poae
  • Poa Patch

Where is it found?:

  • Most prevalent in northern U.S. in cool-season lawn grasses.

What causes it?:

  • Prolonged hot, humid conditions.
  • Compacted soils that don’t drain well.

Brief physical description:

  • Can begin as small circular patches that grow into larger patches up to 18 inches in diameter. These patches can coalesce into larger areas.
  • Affected areas can appear wilted, progressing into reddish-brown or light-brown sunken patches, often with a tuft of healthy grass in the patch’s center.

Best way to treat or prevent:

Good to know:

  • Summer patch is a root disease and, if left unchecked, can damage your lawn.
  • Kentucky bluegrass and fine fescues are most susceptible.
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Necrotic Ring Spot

Also known as:

  • Ophiosphaerella korrae
  • Frog Eye
  • Patch Disease

Where is it found?:

  • Mostly in northern U.S. states.
  • In Kentucky bluegrass lawns.

What causes it?:

  • Cool, wet weather conditions, followed by heat and drought stress.
  • Over-management of your lawn (too much fertilizer and water).
  • The presence of a thick thatch layer.

Brief physical description:

  • Light-green to straw-colored patches usually less than 12 inches in diameter.
  • Regrowth may occur in the center of the patch, creating a “frog eye” appearance.

Best way to treat or prevent:

  • Reduce nitrogen fertilizer.
  • Core aerate regularly to reduce soil compaction and thatch layer.
  • Plant disease-tolerance seed varieties.
  • Fungicide treatments can be iffy, but using a professional-grade fungicide, like Syngenta Headway G or Quali-Pro Propiconazole 14.3 will give you a fighting chance. Make sure you follow label instructions.

Good to know:

  • Buying sod consisting of newer varieties resistant to this disease will help.
  • Sowing your lawn from seed will reduce your odds of getting necrotic ring spot.
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Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the fungus Puccinia graminis, which causes significant disease in cereal crops
Tomasz Klejdysz/Getty Images

Leaf Rust

Also known as:

  • Puccinia spp.

Where is it found?:

  • Throughout the U.S. in all types of lawn grasses.
  • Most commonly, on perennial ryegrass.

What causes it?:

  • The most common cause is the lack of nitrogen fertilizer.
  • Low soil moisture and high humidity.
  • It is most problematic in late summer or early fall.

Brief physical description:

  • Yellow flecks appearing on leaf blades are the first sign.
  • Lawns can take on a yellow or orange tint.
  • These yellow flecks advance into pustules that can burst causing orange powdery spores to release.
  • These rust-colored spores can cover shoes, mowers and even pets. They are not harmful to humans or animals.

Best way to treat or prevent:

Good to know:

  • Leaf rust is a nuisance lawn disease that causes no harm to your turf.
  • A single application of nitrogen fertilizer will provide quick results.
  • No fungicide applications are recommended or needed.
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Barley powdery mildew or corn mildew caused by the fungus Blumeria graminis is a significant disease affecting cereal crops.
Tomasz Klejdysz/Getty Images

Powdery Mildew

Also known as:

  • Erysiphe graminis

Where is it found?:

  • In heavy shade.
  • In slow growing lawns.

What causes it?:

  • Low light intensity.
  • Cooler temperatures, between 60 and 70 degrees and high humidity.
  • Poor air circulation.

Brief physical description:

  • Cobwebby-type growth on the upper surface of leaf blades.
  • In advanced cases, leaf blades appear completely coated with talc or flour.

Best way to treat or prevent:

  • Increase light penetration and air circulation by pruning or removing trees and other vegetation.
  • Reduce watering if areas remain unusually wet for long periods.
  • Lightly fertilize to promote foliar growth. That way you’ll remove the infected leaf blades quicker.

Good to know:

  • Powdery mildew is not harmful to your lawn. There is no need to chemically treat.
  • It can also show up in gardens, perennials and other ornamental plants.
Author
Joe Churchill
Joe Churchill is a self-proclaimed turf nerd with more than 40 years in the professional turf industry, working with professional grass growers from lawn care operators to pro league sports turf managers. His idea of a perfect workday is writing a fertility program or walking a baseball field with a client. He’s always happy to coach beleaguered ...
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Joe Churchill