9 Common Lawn Disorders & How To Prevent Them

Even correctly established, well maintained lawns have their bad days. Among the pests that afflict turf grasses are fungi, mosses, weeds, and insects.

Poorly established or badly maintained lawns, those with poor soil aeration or drainage, improper fertilizing, or clipping are likelier to have diseases than those without these problems. The following are a few of the most common lawn diseases:

  1. Fungi: Brown patch is a fungus disease of nearly all turf grasses, but is worst on Kentucky bluegrass, bentgrass, ryegrass, centipede grass, St. Augustine grass, and fescues in the west. It causes irregular brown spots 1" to several feet in diameter. There is a dark "smoke ring" outer edge where the fungus is active. Excessive nitrogen fertilization aggravates the disease. Control by cutting back nitrogen, minimizing shade/ irrigating deeply, and applying a recommended fungicide.
  2. Dollarspot: Dollarspot is a fungus disease most severe on Kentucky blue-grass, bentgrass, ryegrass, centipede grass, and St. Augustine grass. It causes wet looking, straw-colored spots the size of a silver dollar, which often merge to form large irregular areas of damage. De-thatch, water deeply, and apply a high-nitrogen fertilizer. Fungicides can help control it.
  3. Fairy ring: Fairy ring appears as growing rings of dark green grass, with or without mushrooms, which leave dead grass behind them. Aerate, apply a high-nitrogen fertilizer, and water heavily for up to five days. Fungicides don't work here.
  4. Fusarium: Fusarium patch is common in the central and northeastern U.S., showing up as 2" to 12" tan spots with thin white threads in thatch or dewy grass. Reduce shade, aerate, and improve drainage if possible. Cut down high-nitrogen fertilizers and apply a fungicide in early fall.
  5. Grease spot: Grease spot makes dark and matted leaves in greasy streaks across the lawn. It prefers new lawns. Minimize shade and cut down on water. Check on the best chemical control.
  6. Leafspot: Leafspot causes reddish-brown to purple-black spots on Kentucky bluegrass, and may reach the crown and cause serious damage. To limit damage mow no shorter than 2 inches, fertilize well, over seed with Merion Kentucky bluegrass. Use fungicides 7 to 10 days apart.
  7. Red thread: Red thread is a cool, moist weather fungus that causes small patches of dead grass snarled in bright pink threads, which spread out in 2" to 12" yellowed patches. Reduce shade and apply a high-nitrogen fertilizer in late fall.
  8. Rust: Rust looks like its name and comes off as an orange smudge if you rub the grass with a white cloth. Water, apply a high-nitrogen fertilizer and the right fungicide.
  9. Snow mold: Snow mold is a fungus disease common in the northern region in late fall, winter, and early spring. The fungus cause of the disease likes the cool moist conditions of melting snow. It first appears as a white cottony growth on the leaves, which will kill and turn them brown and matted. Treat by providing adequate drainage, less fall fertilizer, and raking leaves from the lawn.

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