The Morton Arboretum reports that lecanium scale crawlers have emerged on willow. The European fruit lecanium scale is a slightly ovate, reddish brown scale about 1/8 inch in diameter as a mature female. White eggs are laid beneath the adult female’s scale cover in late spring and hatch into reddish crawlers. The crawlers settle down within a week or two. Males develop and emerge as adults later in the summer. Adult male scales are pinhead-sized insects with one pair of wings and a pointed abdomen. They have no functional mouthparts and thus live for only a few days. They fly around and mate with the still immature females, who store the sperm through winter. In spring, the females mature, and eggs are fertilized and laid.

This scale attacks a wide range of trees including maple, hackberry, oak, walnut, hazelnut, and crabapple. It tends to be more numerous on trees under stress. Many trees will have very small numbers of this scale that don’t seem to increase. Thus, trees with light populations should be monitored but will probably not require treatment. Control this scale once the crawlers have emerged. A wide range of insecticides are effective. If a purely contact insecticide (such as summer oil or insecticidal soap) is used, treatment after the crawlers have settled down and molted to the second nymphal stage will probably not be effective. Dormant oil sprays are particularly effective against this insect. Read the label to avoid spraying oil-sensitive plants.