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Hard Scale
(Armored Scale)
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. 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.
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
Treatment
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
Treatment
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
Treatment
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
Treatment
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
Treatment
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.
Please consult with your Arborist for best treatment options.
An integrated approach
When caring for urban trees it is important to make a complete evaluation of all environmental conditions to accurately diagnose all stress factors and prescribe care based on specific circumstances. This prescriptive care will help your tree meet its full potential.
