Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001722
11/12/99
Scale insects
Proper plant care, including pruning of heavily
scale-infested branches (Vis. 1), is a primary management
strategy for scale insects. With certain host plant/scale
combinations, however, supplemental controls are needed.
Most scales overwinter on the plants as eggs underneath
the female scale covering. Many of these can be killed by
dormant oil sprays applied in spring before egg hatch.
Dormant oil applications every few years are capable of
controlling all but the most stubborn scale problems.
Some phytotoxicity or other undesirable effects may result
from use of dormant oils in inappropriate situations. For
example, the waxy "bloom" on blue spruce may be removed by
such a treatment.
Controlling scale insects with insecticide sprays requires
timing the application to coincide with scale egg hatch.
The brief period after egg hatch is the "crawler" stage of
the scale, when the insect is mobile and has not yet
produced a protective waxy coating. When the crawler
stage occurs differs with the scale species and the
weather. After the insect settles and secretes wax, it is
largely impervious to insecticides.
Some insecticides with systemic activity (such as Orthene
or acephate) can be injected into plants or used as a soil
treatment to kill established scale insects. These
materials generally are translocated within the plant in
highest concentrations to the newer growth.
Armored scales
Many people do not recognize these scales as insects.
Instead, they think they are part of the tree or shrub
itself. This is understandable because armored scales are
small (1 to 2 mm), permanently attached, hard, flat,
circular to elongate, crusty scales. Mature scales lack
a distinct head, legs or antennae. Eggs mature underneath
the female scale. The first larval stage hatching from
the egg is called the crawler stage. This is the only
mobile life stage other than the adult male, which is
rarely seen and lives only a few days. Crawlers move
about for several days before permanently settling down on
the plant to feed. Crawlers and very young scale insects
are the life stages most susceptible to insecticides.
Soft scales
These scales have a life cycle similar to that of armored
scales. Soft scales are frequently much larger (up to 6
mm) and softer bodied, and some may move about as adults.
Many soft scales are hemispherical and dark. A related
group of scales produces cottony wax and includes the
cottony maple scale.
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to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
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a commercial product or company.
This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
For more information about this data base or its contents please contact
heatley@msue.msu.edu . Please read our
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