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.
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 dormant oil spray applied to the trunk and branches of a tree in the spring, before the leaves emerge, may reduce the overwintering females. Dormant oil should not be used on Japanese or sugar maple.
A heavy infestation of scale may reduce the vigor of young or stressed trees if no measures are used. Apply sprays in July when young nymphs are present on the leaves. Read the pesticide label for exact usage of the product. Refer to University of Illinois Extension publication " Pest Management for the Home Landscape" for a complete listing of chemical 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.