Blue Spruce Spider Mite Infestation: Identification and Miticide Options

Brown, Web-Covered Clumps on Blue Spruce in Maryland

7-foot spruce has brown, cone-shaped masses of dead needles and webbing. Identified as spruce spider mites.

Damage

• Mottled, yellow-to-brown needles.
• Premature needle drop, twig/branch death.
• Heavy infestations can kill trees, especially during drought.
• Silk webbing collects dust and debris, giving gray appearance.

Management

• Avoid drought-prone, nutrient-poor sites.
• Water heavily during dry periods.
• Chemical: Insecticidal soaps (multiple applications) or miticides (preferred).
  Examples: dicofol, dimethoate.
  Avoid broad-spectrum insecticides—they kill mite predators.
• Do not spray mid-summer (mites less active).
• Spray foliage thoroughly; repeat as needed.