Armored Scales

Hard or Armored Scales are aphid-like insects that produce a hard waxy shell to protect themselves from predators and environmental conditions. Armored scale females resemble legless bumps and damage plants with their sucking mouthparts. The smaller male scales have wings and while in the nymph stage also feed on plants. Female scale continue to feed as they produce hundreds of eggs under each shell . The mature adult female dies, but the eggs survive the winter under the protection of the shell. In the spring and summer of the following year, the eggs hatch into an immature stage called the “crawler” stage.

Armored Scales

The crawlers, also called nymphs move out from under the shell and find a new location on which to feed. As they settle they begin to produce their hard shell. Armored scales feed primarily on the woody tissue of trees. Unlike soft scales and aphids, which feed from the circulatory system of the tree, armored scales feed on the contents of individual cells. Since they destroy cells, they can cause significant dieback of infected stem tissues and in severe infestations, even the death of trees.

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The following scales are common on landscape trees throughout the Twin Cities. Most scale identification will require an experienced professional with a hand lens in order to be correctly identified.

Scurfy Scale
(Chionaspis furfura)

Attacks: young elms, apple, willow, and dogwood
 
What you will see:
 
  • Limb dieback on young trees
  • Small elongate (1/10"), dirty white, pear shaped scales
  • Scales lay flat against the bark

Life cycle:
 
  • Overwinter as adult females
  • Lay eggs in the spring
  • Crawler hatch and emergence occurs in May

Cultural Practices:

  • Maintain tree health
  • Reduce water stress
  • Root enhancement system
  • Mulch

Chemical Treatments:
 
  • Systemic soil application
  • Horticultural oils in Fall
  • Crawler sprays

Obscure Scale
(Melanaspis obscura)

Attacks: Pin and red oaks
 
What you will see:
 
  • Dieback on small branches
  • Small (1/16"), round gray scales
  • Twigs appear covered with silver shells
  • Scales have a black central nipple

Life cycle:
 
  • Overwinter as nymphs
  • Adults develop in the spring
  • Mate and lay eggs in May& June
  • Crawler hatch and emergence occurs in mid to late July
     
Cultural Practices:
 
  • Maintain tree health
  • Reduce water stress
  • Root enhancement system
  • Mulch

Chemical Treatments:
 
  • Systemic soil application
  • Horticultural oils in Fall
  • Crawler sprays

Oystershell Scale
(Lepidosaphes ulmi)

Attacks:Lilac, ash, birch, boxwood, elm, maple, poplar, cotoneaster, willow and many other deciduous trees and shrubs
 
What you will see:
 
  • Dieback in small and large limbs
  • Adult female convex, oystershell-shaped
  • Gray to brown in color
  • Eggs and crawlers are white

Life cycle:
 
  • Overwinter as eggs
  • Crawlers hatch in late May to early June
  • Nymphs mature in late summer to mate
  • Eggs are laid in the summer to early fall
 
Cultural Practices:
 
  • Maintain tree health
  • Reduce water stress
  • Root enhancement system
  • Mulch
     
Chemical Treatments:
 
  • Systemic soil injection
  • Horticultural oils in Fall
  • Crawler sprays

Spruce/Pine Needle Scale
(Chionaspis pinifoliae)

Attacks:Colorado, Norway, white spruce, Arborvitae, cedars, Douglas fir, Hemlock, Junipers, Larch, and Pine.
 
What you will see:
 
  • Thin sparse needles
  • White spots on needles
  • White, waxy scale covering
  • Small infestations can increase within one growing season
  • Extensive needle and branch mortality

Life cycle:
 
  • Red-colored eggs over-winter under the scale covering
  • Eggs hatch in late-May / early June
  • The new crawlers emerge over two week period
  • After mating, the males die and females and produce eggs
  • Two generations per year
  • Second emergence of crawlers appears in late July
  • Each female produces over 100 eggs
 
Cultural Practices:
 
  • Maintain tree health
  •  Reduce water stress
  •  Root enhancement system
  •  Mulch
     
Chemical Treatments:
 
  • Systemic soil injection
  • Horticultural oils in Fall (on non-blue cultivars)
  • Crawler sprays
     
Oak Pit Scale
(Asterolecanium minus)

Attacks: English Oak and White oaks
 
What you will see:
 
  • Immature small yellow scales
  • Mature adult pits (raised bark around the scale)
  • Dead limbs
  • Dieback of small branches
     
Life cycle:
 
  • Oak pit scales overwinter as adults
  • Scale nymphs (crawlers) are produced starting June
  • Crawlers can be produced for as long as five months
  • The highest crawler population occurs in early summer
  • Crawlers colonize current season and one year old wood
  • One generation per year
     
Cultural management:
 
  • Ineffective with large populations
  • Enhance tree vigor to replace infected tissue
     
Chemical Management:
 
  • Systemic soil injections
  • Horticultural oils
  • Long residual insecticides (must time for crawler stages)

Management of armored scales is more difficult than for soft scales and aphids, since their hard shells protect them from most topical insecticides. Fortunately there are insecticides that can be used to systemically treat hard scales. The scales ingest this insecticide while feeding and one treatment will usually provide enough control to reduce most hard scale populations to non-damaging levels.
In severe scale infestations this soil injection treatment should be combined with a growing season spray for the susceptible crawler stage of the scale species followed by a late season horticultural oil spray to suffocate any remaining over-wintering scales. Horticultural oils should not be applied when the temperature will be above 80° F or on plants with a blue coloration. Oils will remove the blue color from blue spruce, fir and other plants where the wax is blue.