Looking Out for Common Diseases on Your Lawn

Just a quick reminder on common lawn diseases that you might encounter as we head into the summer season. For diseases with an irregular pattern, be on the lookout for powdery mildew, rust, and leaf spot or melting out. Here are a few quick visual diagnostic tips for these diseases:

  • Powdery mildew - dusty white to light gray powder on leaf surfaces; leaf yellowing
  • Rust - From a distance, turf appears orange to rusty in color. On close examination, leaf blades have bright orange to reddish-brown pustules.
  • Leaf spot or Melting out - elongated to circular spots with purple to black margins and brown, or light tan centers with yellow area surrounding leaf and crown lesions.

If affected areas are circular in pattern, watch out for dollar spot, fairy ring, necrotic ring spot, and summer patch.

  • Dollar spot - affected areas extend 2 to 6 inches in diameter, leaf lesions are irregular and bleached white or tan surrounded by dark brown to reddish-purple margins and typically appear in the middle of the leaf.
  • Fairy ring - an outer ring of dark green grass surrounds dead grass inside. Patch can grow up to 20 feet in diameter.
  • Necrotic ring spot and Summer patch - small circles of dead grass surrounding a tuft of green grass ("frog-eyes"), 6 to 12 inches in diameter. Necrotic ring spot occurs in wet cool conditions (58 to 82F) and summer patch is more active on high summer temperatures (85 to 95F).

    Preventing fungal lawn diseases is a lot easier than trying to cure them. This can be done by planting resistant varieties; aerating to improve root growth, soil drainage and air exchange; dethatching, fertilizing properly, and watering deeply but infrequently especially during dry periods of summer and fall. Chemical sprays may be helpful but are only effective when applied before the disease becomes severe, and may not be necessary when proper cultural practices are followed.

    This article originally appeared in the June 11, 1999 issue, p. 77.

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