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

The treatment strategy for azalea bark scale primarily targets young nymphs because they are unprotected by their waxy covering.  Dormant horticultural oil sprays can be used in the fall after the growing season is complete when they are preparing to overwinter.  During the growing season spray and soil applied systemic options are available.

 

 

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Azalea Bark Scale Treatment Option 1

During the dormant season and early spring horticultural oil can be applied as a bark and limb spray to control nymphs.  Once plants have leafed out, however other options should be used

Application MethodTrunk and Limb Spray

DIY Equipment Needed:

• RTSA Horticultural Oil

• Hand pump sprayer with wand

• Gloves

• Safety glasses

Azalea Bark Scale Treatment Option 2

In spring through early summer a soil application of a systemic insecticide, such as Transtect will target feeding nymphs and adults.  Apply early in the season for season long control of azalea bark scale.

Application MethodSoil drench

DIY Equipment Needed:

• Transtect™

 Measuring or diameter tape

• For Soil Drench – bucket, watering can or soil drench kit

Azalea Bark Scale Treatment Option 3

If you choose to apply once symptoms are visible in the late spring through summer, a great option is the insect growth regulator Distance mixed with horticultural oil.  Apply the solution to trunk and major limbs for 14-21 days of control.

Application Method – Trunk and Limb Spray

DIY Equipment Needed:

 RTSA Horticultural Oil and Distance

 Hand pump sprayer with wand

 Gloves

 Safety glasses

Azalea Bark Scale DIY Kit

Option One:

Application Method – Trunk and Limb Spray

DIY Equipment Needed:

 RTSA Horticultural Oil

 Hand pump sprayer with wand

 Gloves

 Safety glasses

Option Two:

Application Method – Soil drench

DIY Equipment Needed:

 Transtect™

 Measuring or diameter tape

 For Soil Drench – bucket, watering can or soil drench kit

Option Three:

Application Method – Trunk and Limb Spray

DIY Equipment Needed:

 RTSA Horticultural Oil and Distance

 Hand pump sprayer with wand

 Gloves

 Safety glasses

How Is It Spread?

  • Eggs are deposited into the white waxy egg sac in late April
  • Crawlers hatch out of eggs in June-July or 957 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)

Susceptible Trees

Rhododendron spp, azalea, huckleberry (Vaccinium spp.).

Symptoms

  • Leaf yellowing is often visible after June or July.
  • Sooty mold growing on honeydew can be found under tree or on limbs.
  • Branch dieback.
  • White waxy threads of the females egg sac near twig crotches prior to June or July.
  • Small winged adults males are generally on leaves around August through September.
  • Crawlers are reddish, tiny, mobile, and typically found around June or July.

Lookalikes

  • Only rhododendrons and vaccinium spp. become infested
  • White stringy covering is distinctive
  • Branch crotches are preferred

Timing

Spring and Summer

Urgency

Moderate

Risk of Spreading

Moderate

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