Monday, January 14, 2008

Cottony Maple Scale



Homoptera: Coccidae, Palvinaria innumerabilis



PLANTS ATTACKED: Maples and dogwood primarily, but also many woody ornamentals.

DESCRIPTION: Heavily infested plants will have large numbers of scales on the branches and twigs. Large numbers of feeding scales will reduce the amount of nutrients reaching the leaves and will cause them to turn yellow and fall prematurely. Scale insects feed on plant sap with their long thread-like mouthparts (stylets), which are six to eight times longer than the insect itself. Feeding by scales slowly reduces plant vigor. Heavily infested plants grow poorly and may suffer dieback of twigs and branches. Occasionally, an infested host will be so weakened that it will die.

IDENTIFICATION: During the winter the cottony maple scale is in the immature stage and is small, oval and flattened in shape, and pale green in color. During the warm temperatures of spring, the scale reaches maturity and, by late spring, the brown, elongate scale has a characteristic white, cottony egg mass attached to it.

LIFE HISTORY: Eggs are laid in April and June and hatching occurs throughout the early summer. Crawlers settle on leaves and stems. Male scales complete development by fall and mate with the immature females. Before the leaves drop from the trees, the female scales migrate to the stems and twigs to overwinter. In spring the female reaches maturity and lays a distinctive cottony egg mass. There is one generation per year.

CONTROL: Crawlers are usually out between June 5 and June 25 in Virginia. Treat June 10 and 20. Adult scales are protected from insecticides by waxy coverings. Control measures, therefore, must be aimed at unprotected immatures, called crawlers, which are only out for a short time. Dormant oil can be applied to the overwintering stages in late spring before new growth starts. During the growing season, when dormant oil cannot be used, insecticide treatments must be timed correctly to eliminate the crawler stage. See the Virginia Pest Management Guides for specific insecticides for control. Care should be taken when applying insecticides, because they may deplete the number of natural enemies that normally control the pest insects.

REMARKS: Cotton maple scales are heavily fed upon by natural enemies and, in some cases, chemical controls are not needed. English Sparrows, feeding on the scales are thought to be important in reducing populations. This scale is sometimes confused with Maple Leaf Scale, which produces its egg mass on the leaves. The Cottony Maple Scale produces its egg mass primarily on the branches and stems.

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