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Description
The overwintering form of the cottony maple scale is a small,
brown, flattened 1/8 inch long scale attached to the bark
of twigs and small branches. During the summer, the scale
enlarges by secreting wax resulting in a body several times
greater than the overwintering form. The body of the scale
is white and resembles a kernel of popcorn. The immature scale
is flat, oval shaped, and light yellow to green. The eggs
are usually brown.
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version
Figure 1. Cottony Maple Scale
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Life
History
The cottony maple scale is common on maple, boxelder, hackberry,
dogwood, beech, apple, oak, linden, honeylocust, and elm. The scale
overwinters as an immature female on the twigs of the host. By late
spring the insect has developed into a mature female and begins
laying as many as 1,000 eggs. The eggs hatch into crawlers in late
June and July and move from the twigs to the leaves where they feed
along the midrib or the veins. Late in the summer, mature winged
males mate with immature females. The males die within a few days
after mating as they are unable to feed. Before leaf drop in the
fall, the immature females move back to the twigs to overwinter.
There is one generation per year.
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Figure 2. Cottony Maple Scale on Silver Maple Leaf
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Damage
Damage to the host tree is caused in several ways. If scale
populations are heavy, dieback of branches and twigs may result.
In severe cases the tree may die. Feeding by the scales may
result in heavy concentrations of honeydew. This honeydew
is readily colonized by sooty mold fungi which will result
in a blackened appearance to leaves, twigs, and branches.
In some cases, premature leaf drop may also occur due to scale
feeding. The honeydew also becomes a nuisance due to deposits
on automobiles and lawn furniture located under infested trees.
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Nonchemical
Control
There are a number of natural enemies of the cottony maple
scale including a number of wasp and fly parasites. Natural
predators such as various species of lady beetles feed on
the immature scales situated on the leaves. Outbreaks generally
buildup over a period of years and then disappear due to natural
enemies and climatic factors. Well established and vigorously
growing trees are usually able overcome the infestation.
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Figure 3. Cottony Maple Scale Crawlers
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version
Figure 4. Wasp Parasite of Cottony Maple Scale
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Chemical
Control
If scales are heavy on stressed or unestablished trees, a
crawler spray may be applied in July in order to prevent dieback
and decline. A dormant oil spray applied to the trunk and
branches of the tree may also be used to reduce overwintering
female populations and eliminate the risk of killing off beneficial
insects such as lady beetles and parasites.
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