Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Cottony Maple Scale
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The
cottony maple scale is a highly modified insect pest that commonly attacks
silver and red maples in Ohio. The scales, are usually first noticed when the
females produce an egg sac which appears as a ¼ to ½ inch long ball of
cotton. Heavy infestations can result in branches being turned completely
white with the egg sacs. Like most scale insects, the nearly mature insects,
the adults and the eggs are resistant to pesticides and the anxious tree
owner must wait until the correct time for management. |
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Plants Attacked
Cottony
maple scales reach epidemic numbers' on silver maple but noticeable populations
can occur on red maple. It is also known to be able to survive on other species
of maple, honey and black locust, white ash, euonymus, oak, box elder, dogwood,
hackberry, sycamore, beech, elm, willow, basswood, and poplar.
Damage
Normally,
this scale is a mere curiosity and nuisance. The white egg sacs easily attract
attention and the developing scales produce honeydew. Honeydew is the excess
water and sugar excreted by many plant sap-feeding insects. Honeydew is
commonly mistaken for "plant sap" being dropped on cars, sidewalks
and lawn furniture lying under trees. When honeydew collects on leaves and
branches, bees, wasps and ants are attracted to the area. If the honeydew is
allowed to remain, molds called "sooty fungus" grow on the material,
turning the surface a gray-black color.
Occasionally,
heavy outbreaks of this scale occur, usually on weakened or stressed trees.
These outbreaks can cause the death of numerous small branches and occasionally
the death of a tree.
Description and Life Cycle
Mature
cottony maple scales are small, flat, oval, brown insects without obvious legs,
antennae or wings. They are firmly attached to the twigs and branches of various
trees and may be 1/4 to 3/8 inch in diameter. At maturity, the females produce
the white, cottony egg masses (called ovisacs) over a period of several weeks.
The “cotton" is really waxy threads and the ovisacs may contain over 1,500
eggs. These eggs hatch from mid-June to August and the young nymphs are called
scale crawlers. These microscopic crawlers are small, flat, oval insects with
two distinct eyes, short antennae and tiny legs. The crawlers walk onto the
leaves and tend to attach alongside the major leaf veins, usually on the
underside. Here, the nymphs produce copious amounts of honeydew and grow by
molting once. By this time the scales look like two different kinds, translucent
white to pink for and a larger, flat, tan form. These are males and female
scales, respectively. In September, the male scales emerge as tiny winged
gnat-like insects that move around on the leaves in search of females. After
mating, the males die and the females soon withdraw their mouthparts and crawl
back onto small twigs and branches. Here, the reinsert their mouthparts and
settle down for the remainder of their life. These females first appear
greenish with a white powdery coating and they are about 1/8-inch long. By
winter, they have turned buff in color and in the following spring and early
summer they turn a chestnut-brown. When the sap begins to flow in the spring,
the females continue to grow and' they again produce considerable amounts of
honeydew. By late May to early June the females have matured and they begin to
produce their ovisacs.
Control Hints
This
pest has numerous parasites and predators that normally keep its populations in
check. However, every few years, these natural controls seem
to fail and the cottony maple
can reach epidemic proportions. Unfortunately, weak trees can be severely
damaged during these outbreak years. Healthy trees often loose a few small
branches and have no apparent long term problems.
Strategy 1: Cultural and
Biological Control
– Silver maples in restricted street lawns or suffering other stresses from
drought, compacted soils, poor fertilization, etc. are the ones most likely to
exhibit major branch or crown dieback. Improving the tree growing conditions
will significantly help the trees survive the cottony maple scale attacks until
the natural predators and parasites build up to effective levels.
Strategy 2: Use “Soft” Pesticides – Soaps and horticultural oils
can be very effective in managing the freshly settled crawlers. Insecticidal soaps or horticultural oil must
be applied thoroughly to the leaves, both to the underside and upper surfaces,
in order to kill the scales. Soaps and
oils only kill the pests on contact.
Strategy 3: Standard Insecticide
Applications –
Several insecticides are registered for control of scale crawlers and newly
settled crawlers. These pesticides,
again, often need to be applied in sufficient spray quantity to wet both the
leaf upper and lower surfaces.
Strategy 4: Dormant Oils Sprays - Dormant oil sprays have been
traditionally used to manage many scales on ornamental trees.
Information obtained through the Ohio State Extension Factsheet HYG-20 19-95
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES