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Cottony Maple Scale

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Cottony Maple Scale

Cottony maple scale is one of the largest and most conspicuous soft scale insects that attack ornamental plants. Its favored host is silver maple.

Cottony Maple Scale

Cottony Maple Scale

The Acer saccharinum . A large number of other deciduous trees are also attached including other species of maple, such as boxelder, A. negundo ; basswood, Tilia americana ; white ash, Fraxinus americana ; dogwood, Cornus spp ; locust, Robinia spp .; hackberry, Celtis spp .; sycamore, Platanus spp .; birch, Betula spp .; elm, Ulmus spp .; willow, Salix spp .; and poplar, Populus spp .

Eggs masses are conspicuously white and cottony in appearance. Each mass usually contains 1,000-1,500 eggs. Male scales are tiny, winged insects. Immature females are flat and inconspicuous. Mature females are pale to dark brown, convex, and about 3-6 mm long . The cottony maple scale is most easily recognized by the characteristic egg masses on twigs and branches.

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 over a period of several weeks. The "cotton" is really waxy threads and the ovisac may contain over 1,500 eggs. These eggs hatch from mid-June to August and the young nymphs are called scale crawlers.

Cottony Maple Scale 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, a translucent white to pink form 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.

Damage:Severely infested trees appear as though they were covered with a string of popcorn. Heavy scale insect populations withdraw plant fluid and cause dieback of twigs and branches. Under severe conditions an infestation may kill the entire tree. Also, when this soft scale feeds on leaves and twigs, a large quantity of honeydew is excreted. Honeydew promotes the growth of a black sooty mold, that imparts a blackened appearance to leaves, twigs, branches, and other substrates beneath an infested host plant. In some cases, premature loss of foliage may result from an infestation of this soft scale insect.

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.

Cottony Maple Scale

Cottony Maple Scale

Control:Soaps and horticultural oils can be very effective in managing the freshly settled crawlers. These materials also have a minimal adverse affect on the adult lady beetles and parasites already in settled crawlers. Insecticidal soaps or 1.5% 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. Application of soaps or oils should be made in mid-July and again in early August, if additional crawlers are found.

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. Apply registered products in mid-July and again in the second week of August for best control. See OSU Extension Bulletin 504 for insecticides currently registered for scale crawlers.Dormant oil sprays have been traditionally used to manage many scales on ornamental trees. Unfortunately, many maples are sensitive to these oil sprays and significant small branch dieback or spring leaf drop can occur, if the dormant oil was applied after the maple sap has begun to flow.

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