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Importance - Many different
types of scales effect hardwoods and conifers throughout the
United States. A large scale population can reduce growth,
weaken the tree, and cause branch or crown dieback. Scales
are usually of greatest concern in nursery stock, seed
orchards, and shade and ornamental trees. Honeydew and sooty
mold, associated with scales, usually mar the beauty of
ornamentals.
Scale insects are often inconspicuous pests of
many evergreen and deciduous plants. They can occur
on leaves, twigs, branches or trunks. Their small
size and general lack of mobility make them
difficult to notice by the casual observer. Scales
derive their name from the shell-like, protective
covering they form over themselves. Scale insects
are broken into two categories:
Soft Scales—generally
secrete an attached, thin, waxy layer over
themselves. The soft covering they secrete
cannot be separated from the scale's body. Soft
scales typically move between branches and
leaves during their lifecycle. They also produce
honeydew.
Armored (Hard) Scales—use
shed skins and wax that is unattached to their
body to form their hard, shell-like cover. These
covers can be separated from the scale's body.
Hard scales typically do not move to leaves
during their lifecycle and also do not produce
honeydew.
Immature scales, upon hatching from eggs, are
soft-bodied, mobile and are termed "crawlers." These
crawlers seek suitable sites in which to feed,
secrete their protective shell, and mature to
adulthood. The immobile, "shell stage" of scales are
adult females; males are small, fly-like and
infrequently seen. |
Identifying the Insect -
Scale insects vary in shape and form. There are soft bodied,
hard-bodied or armored scales. They may resemble a small
turtle or oyster shell or even part of the bark of the tree.
Some scales are white and very obvious; others are dull and
perfectly match their host's color. Therefore, close
examination is very important. They can range from 1/50 to
3/10 inch (1/2 to 7 mm) in length. Scale insects can be
found on any part of a tree.
Identifying the Injury -
Trees with poor vigor or with branch and crown dieback
should be examined closely for scales. Scale feeding may
cause some abnormal plant growth at the point of attack,
such as stunting of leaf or shoot growth, leaves turning
yellow or red, and branch gouting. Other symptoms to look
for are early leaf drop or dieback or "flagging" of newly
formed terminals, branch ends, and new leaves. Ringlike
swellings or pits in the bark cause a rough appearance of
branches. Heavy infestations will kill trees. Sooty mold and
ants frequenting a tree are good indicators of scale
infestations. |
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