Azalea Bark Scale Diagnostic Guide
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.
Shrubs at Risk
Rhododendron, azalea, and huckleberry are all known to be infested by azalea bark scale.
Signs of Damage
- Leaf yellowing mid to late summer.
- Sooty mold growing on honeydew can be found under the tree or on limbs.
- Dieback from the tips inward is common.
- White waxy threads of the female egg sac near twig crotches are visible prior to June/July.
- Small winged adults (males) are on leaves around August/September.
- Crawlers are reddish, tiny, and mobile and found around June/July.
- Adult females resemble mealy bugs.
- Eggs are deposited into the white waxy egg sac in late April.
- Crawlers hatch out of eggs in June-July or 957 growing degree days.
- Crawlers prefer branch crotches and twigs where they insert their mouthparts.
- Overwinter as nymphs.
- There is one generation per year (possibly two in southern states).
Nymphs must be targeted when they are unprotected by the waxy covering. This means dormant horticultural oil sprays may be used after the growing season is complete. A more effective option is to apply a systemic insecticide either during the prior fall or spring to control feeding crawlers from the inside of the plant.
Management of this pest is easiest when the nymph stage is targeted. Soil applied systemics have made application timing and methods much easier.
A Diagnostic 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 forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org