The cottony maple scale is a large, flat, brown scale insect found on the twigs and branches of various trees. The white cottony egg masses, which resemble popcorn, are the most distinguishing feature of this scale. A favored host is silver maple, but it will attack other species of maple as well.
Other host preferences include:
- black locust
- white ash
Effects on the host tree
Injury to trees is caused by the scale insect sucking juices from the twigs and branches. Small twigs begin to die first, followed by leaves becoming stunted and a black, sooty mold appearing on the tree and objects beneath the tree. A heavy infestation of two or three years may result in death of large branches.
Spread of the infection
The fertilized, immature females spend the winter on the twigs and small branches of the host. In the spring, they resume their feeding and development. In late May, the females begin producing eggs that are deposited into masses covered with white silken fibers. The young scales, called "crawlers," begin hatching in mid-June through early July.
The crawlers then move up and down twigs and out onto leaves before settling down to suck juices and secrete a waxy coating over themselves. Just before leaf drop in the fall the mated females migrate back to the branches where they settle and overwinter.
Treatment and Management
A horticultural oil treatment may be applied before growth starts in the spring or after leaf drop in the fall. An additional treatment may be applied in mid-August or September after the crawlers have hatched and settled on the leaves. However, do not treat sugar maples with oil; this species reacts adversely to oil and branches may die.
It is extremely important to restore plant vitality, because tress weakened by the scale are more susceptible to other insects, diseases and environmental stress. Fertilizing, mulching and watering, especially during dry periods, are recommended to help maintain tree health.