Azalea Bark Scale

Discovered in 1881, the azalea bark scale, Eriococcus azaleas, is a prominent pest of rhododendron, azalea, and huckleberry (Vaccinium spp.). It has been reported in the Eastern US, as well as Belgium and Russia. This is a pest that generally does not kill hosts, rather it causes aesthetic damage. Honeydew can be an inconvenience as well.

Treatment Strategy

Nymphs must be targeted as they are unprotected by the waxy covering. This means dormant horticultural oil sprays may be used after the growing season is complete. This is when nymphs are preparing to overwinter. Two other options are available to treat for crawlers; both spray and systemic.

Other Treatment Practices

  • Maintain plant health and monitor closely for this insect.
  • Adequate water is a key factor in maintaining stress free plants. A slow, deep watering event once every few weeks during dry conditions will help maintain soil moisture levels and minimize stress.
  • Mulch is very beneficial for all trees because it reduces competition with turf and moderates soil temperature and moisture levels. The addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy fibrous roots.
  • Do not over fertilize, as it can lead to increased scale populations.

Limb/Foliar Spray or Soil Application Using Transtect

Soil Application or Limb/Foliar Spray Using Xytect 2F

Soil Application or Limb/Foliar Spray Using Xytect 75WSP

Foliar Spray Using RTSA Horticultural Oil

Foliar Spray Using Proxite + RTSA Horticultural Oil

Expected Results

Management of this pest is easiest when the nymph stage is targeted.

Signs of Damage

  • Chlorosis after June/July
  • Sooty mold growing on honeydew can be found under tree or on limbs
  • Twig dieback
  • White waxy threads of the females egg sac near twig crotches prior to June/July
  • Small winged adults are males, generally on leaves around August/September
  • Crawlers are reddish, tiny, and mobile. Found around June/July or 957 GDD

Photo: Clemson University
USDA Cooperative Extension Slide Series, Bugwood.org

Photo: United States National Collection of Scale Insects Photographs Archive
USDA Agricultural Research Service Bugwood.org

Trees At Risk

  • Rhododendron spp.
  • Azalea
  • Huckleberry (Vaccinium spp.)
  • Andromeda
  • Willow
  • Maple

Biology

  • Eggs are deposited into the white waxy egg sac in early spring.
  • Crawlers hatch out of eggs in late spring –early summer (400-1500 GDD)•Crawlers prefer branch crotches and twigs where they insert their mouthparts.
  • Overwinters as nymph.
  • There is one generation per year (possibly two in southern states).

A Treatment Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments by forestryimages.org

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