The primary hosts of cottony maple scale (Pulvinaria innumerabilis) are silver maple and boxelder. It can also infest other maples, white ash, hackberry, dogwood, beech, apple, oak, linden, elm, black and honey locust.
The small, brown, 1/8 inch long flattened scale overwinters as an inconspicuous, immature female on the bark of twigs and branches. By late May or early June the female scale has matured and begins to lay hundreds of eggs within a white frothy wax. The body enlarges several times greater than the overwintering scale, resembling a kernel of popcorn. The eggs hatch into pale yellow-green crawlers in late June or July and migrate to the underside of leaves, feeding along the veins and midrib by withdrawing sap from the plant parts.
In late summer, mature winged males mate with immature females. The males, lacking feeding mouth parts, die a few days after mating. Before leaves begin to drop in fall, the immature females migrate to the twigs where they attach themselves for overwintering. They produce one generation per year.
Damage to the host tree is caused when heavy populations of cottony maple scale withdraw sap from the plant, resulting in branch and twig dieback. Leaves may turn yellow and drop prematurely. In extreme conditions, a tree may be killed. Frequently, feeding results in the secretion of a clear sticky substance called honeydew. Honeydew often drops onto leaves or plants below. If abundant, a sooty mold fungus may colonize the honeydew, resulting in a black sooty appearance on the leaves, twigs, and branches.
Serious outbreaks of the cottony maple scale may last for two to three years, but their numbers become greatly reduced when natural predators, including a number of wasps and fly parasites, are present. The major predator of the immature scale is the twice-stabbed lady beetle. The adult beetle is black with a red spot on each wing. The immature lady beetle resembles a mealy bug and can be found buried in the cottony egg mass. Both adult and immature beetles feed on eggs and nymphs of the scale. When beneficial insects are present, spraying should be avoided.
A heavy infestation of scale may reduce the vigor of young or stressed trees if no measures are used. Contact the Plant Clinic (630-719-2424 or firstname.lastname@example.org) for current recommendations. Use pesticides safely and wisely; read and follow label directions. The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.