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Description
Lecanium scales vary greatly in size, color, and shape, depending
somewhat on the host plant they inhabit. In general, after egg-laying
the female scale turns brown, becomes brittle, and hemispherical.
Before egg-laying, the scale may be quite flat or highly convex
and may range from a light tan to a purplish-white. The lecanium
scales range in size from the 1/8-inch terrapin scale up to the
1/2-inch hickory lecanium scale.
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The
different lecanium scales show distinct preferences for particular
hosts. Fletcher scale prefers arborvitae and yew; terrapin
scale, maples and peach; hickory lecanium scale, hickory and
elm; globose scale, stone fruits; and European fruit lecanium
scale, a wide variety of shade and fruit trees, shrubs, and
woody ornamentals.
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Click on image for larger
version
Figure 1. Lecanium Scales
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Life
History
Most species of lecanium scale deposit their eggs during June or
early July. As the eggs are laid, the body of the female becomes
increasingly dry and hemispherical. The dead, brittle body of the
female, the "scale," protects the eggs until they hatch.
The emerging crawlers migrate to the leaves, except for Fletcher
scale crawlers which remain on the branches of the arborvitae and
yew throughout the year. In the late summer, after shedding their
skins once, the crawlers return to the twigs to overwinter. The
scales resume that development the following spring and undergo
a period of rapid growth that continues into early summer and egg-laying.
The
terrapin scale differs from most lecanium scales in that the young
are born as crawlers in the spring. These crawlers migrate to the
leaves where they remain until just before frost. It is the adult
female, not the second-stage nymph, that overwinters. Generally,
the terrapin scale and other lecanium scales have only one generation
a year.
Damage
The lecanium scales, like other scale insects, feed on the sap of
the host plant. If a tree is heavily infested, the competition for
moisture among the lecanium scales will cause some dieback of twigs
and branches, and premature leaf drop. During severe moisture stress,
a heavy infestation could kill the entire tree. The heaviest damage
occurs during the spring and early summer. In addition to causing
moisture loss, lecanium scales produce honeydew that is colonized
by black, sooty, mold fungi. Fletcher scale seldom causes any visible
injury to arborvitae, but is a serious pest of yews.
Nonchemical
Control
As with other scale insects, the populations of lecanium scale normally
are regulated by the physical environment and natural parasites
and predators.
Chemical
Control
Crawler sprays should be applied around mid-June, and repeated two
weeks later. Dormant oil sprays may also used for overwintering
immature females.
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