Turf Magazine - June, 2009

TURF SCIENCE

Diagnosing Lawn Problems

By John C. Fech
Photo by Tom Eickhoff, UNL.
Billbug damage to turf.

Some turf managers go about lawn problem diagnosis systematically; others use an accumulated set of anecdotal experiences. It’s all about paying careful attention to the signs and symptoms and narrowing down the list of possible problems.

One of the most important factors is the influence of the season on the likelihood that a particular causal agent is responsible. It’s rare that turf declines from only one cause. In almost all cases, factors such as thatch, soil drainage, traffic and pH work with a disease or insect to cause the problem.

Consider options by season

Early spring—cold weather, 32 to 45 degrees
Relatively few problems occur solely in cold weather.

• Are there irregular patterns or streaks in the turf?

Possibilities:

  1. Winter Desiccation—bleached or dead grass, especially in windswept areas.
  2. Spring Frost—new leaves killed back following freezing temperatures.

• Is the turf dead in the wettest areas?

Possibilities:

  1. Water or Ice Damage—affected areas follow drainage patterns.
  2. Pink Snow Mold—circular patches of dead turf, 2 inches to 2 feet in size. Wet grass covered with white to pink mold; no sclerotia present.
  3. Gray Snow Mold—circular patches of dead turf, 2 inches to 2 feet in size. Wet grass covered with white to gray to bluish-gray mold; minute yellow to brown to reddish sclerotia present.

Spring—cool weather—45 to 60 degrees
A larger group of possible causes can injure turf in cool weather.

• Are there circular patches or rings of adversely affected turf?

Possibilities:

  1. Fairy Rings—arc-shaped rings 3 to 15 feet across; outer ring usually contains darker green grass.
  2. Zoysia Patch—patches of dead grass 2 to 10 feet appear as dormancy breaks in spring.

• Are there irregular patches of adversely affected turf?

Possibilities:

  1. Powdery Mildew—milky white to gray mold; found mostly in shade; turf becomes thinned.
  2. Stripe Smut—gray to black streak in leaves; leaves split into ribbons and curl. Grass later dies in irregular patches and undergoes a general thinning.
  3. Red Thread/Pink Patch—pink to reddish cottony growth on leaves and sheaths, and/or red, threadlike growths extending beyond the leaf tip; may appear tan in patches.
  4. Bipolaris/Dreschlera Leaf Spot—leaves with purplish to brown spots, usually causes thinning and crown rot.
  5. Ascochyta Leaf Spot—purplish to chocolate brown spots that enlarge and become tan to straw colored.

Late spring, early summer, early fall—warm weather—60 to 75 degrees
Perhaps the largest group of possibilities occur in warm seasons.

Photos by John Fech, UNL.
Dollar spot damage. Waterlogged soils can impact turf injury.

• Are there round straw-colored patches in turf, 2 to 7 inches across?

Possibilities:

  1. Dollar Spot—whitish leaf spots with brown or reddish borders. Patches 2 to 4 inches across.
  2. Pythium Blight—sunken, straw-colored patches, 2 to 6 inches, grass leaves matted down.

• Are there patches or rings 2 to 3 feet across, usually with green centers?

Possibilities:

  1. Necrotic Ring Spot/Summer Patch—Tan to reddish-brown patches or rings with blackened stem bases and roots.

• Are there rings or arcs 3 to 15 feet across?

Possibilities:

  1. Fairy Rings—arc-shaped rings 3 to 15 feet across; outer ring usually contains darker green grass.

• Are there mostly irregular patterns in turf?

Possibilities:

  1. Powdery Mildew—milky white to gray mold; found mostly in shade; turf becomes thinned.
  2. Rusts—bright yellow-orange or reddish-brown pustules present.
  3. Slime Molds—turf laden with superficial blue gray, ash gray, creamy yellow or black powdery structures on leaves; easily wiped off.
  4. Red Thread/Pink Patch—pink to reddish cottony growth on leaves and sheaths, and/or red threadlike growths extending beyond the leaf tip; may appear tan in patches.
  5. Bipolaris/Dreschlera Leaf Spot—leaves with purplish to brown spots, usually causes thinning and crown rot.
  6. Bluegrass Billbugs—leaves are straw brown and easily pull loose from crown with a light tug. Inside of stems hollowed out with beige powdery frass present.
  7. Ascochyta Leaf Spot—purplish to chocolate brown spots that enlarge and become tan to straw colored.

Summer—hot weather—over 75 degrees
In the summer heat, the effects of most causal agents are intensified by heat stress and drought.

• Are there round patterns in the turf?

Possibilities:

  1. Pythium Blight—sunken, straw-colored patches, 2 to 6 inches, grass leaves matted down.
  2. Dollar Spot—whitish leaf spots with brown or reddish borders. Patches 2 to 4 inches across.
  3. Necrotic Ring Spot/Summer Patch—Tan to reddish-brown patches or rings with blackened stem bases and roots.
  4. Brown Patch—light brown, grass blades usually not matted down. Irregular blotches appear on the leaf blades.
  5. Fairy Rings—arc-shaped rings 3 to 15 feet across; outer ring usually contains darker green grass.

• Are there irregular patterns in the turf?

Possibilities:

  1. Bipolaris/Dreschlera leaf spot—leaves with purplish to brown spots, usually causes thinning and crown rot.
  2. White Grubs—roots eaten, leaves brown and thin, turf pulls back like a piece of carpet.
  3. Bluegrass Billbugs—leaves straw brown and easily pull loose from crown with a light tug. Inside of stems hollowed out with beige powdery frass present.
  4. Rusts—bright yellow-orange or reddish-brown pustules present.
  5. Slime Molds—turf laden with superficial blue gray, ash gray, creamy yellow or black powdery structures on leaves; easily wiped off.

Maladies that occur regardless of season or weather conditions

• Has the turf gradually become pale green to yellow, is growing slowly and has thinned?

Possibilities:

  1. Iron Chlorosis—interveinal yellowing of younger leaves, chlorosis of older, lower leaves
  2. Nitrogen Deficiency—stunting of growth, older leaves lose green color, resulting in a thin stand.

• Does the turf suddenly appear scorched?

Possibilities:

  1. Chemical or Mower Burn—brown leaves and stems, usually in patches, streaks or bands.
  2. Fertilizer Burn—bands, streaks or irregular patterns; grass is stimulated at margins of injury.
  3. Dog Injury—ring of dark green grass at margin; patches are up to 1 foot across.
  4. Scalping Injury—entire turf area or patches over slight elevations or mowing corners are yellow to brown.
  5. Dull Mower Injury—leaf tips are shredded; appear gray, then tan.

• Are there regular to irregular patches of dead and dying turf?

Possibilities:

  1. Thick Thatch or Buried Debris—thatch in excess of 5/8 inch or construction remnants present.
  2. Sod Webworms—thinned turf; presence of tunnels, silken webs and webworms.

• Is the turf bare or thinned (often in traffic areas) with dense shade or waterlogged soils?

Possibilities:

  1. Algae—greenish to brown scum that later forms a black crust.
  2. Moss—small green plants that grow on soil in slight mounds.
  3. Compaction—soil hard in heavily trafficked areas, on paths, under playground equipment.

• Is the turf dry, bluish green, wilted, and turned brown?

Possibilities:

  1. Drought, Wilt or Improper Watering—plants with slow growth, withered stems.

Once you’ve determined the likely cause, confirm your suspicion in various turf pest books, including “Controlling Turfgrass Pests” by Shurtleff, Fermanian and Randell, “Managing Turfgrass Pests” by Watschke, Shetlar and Dernoeden and “The Turfgrass Problem Solver” by Turgeon and Vargas.

John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln.