Origin:
Uncertain, as some references indicate it is a native species while others indicate it entered the U.S. in San Francisco in the early 1900’s, and from there spread throughout the U.S. Now an extremely common pest of ornamental trees and shrubs, including liquidamber, elm, magnolia, locust, crabapple, maple, pyracantha, and all stone fruit trees such as peach, apricot, and plum.
Biology:
Typical scale biology with mature females overwintering on the host plant, producing eggs beneath their wax shell in the spring, with first instar crawlers emerging in mid to late spring. The crawlers are mobile and move to the leaves to feed on them during the summer. Prior to molting to the second instar they move back down to tender stems where they become sessile and create the wax shell over themselves, and never move from that spot.
Identification:
A very distinctive scale with a large wax shell that is solid black with 4 rows of white to yellowish spots across it. As they age the lighter spots tend to diminish in size, but are still faintly visible.
Characteristicts Important to Control:
The major problem is the heavy production of honeydew, and light infestations cause no visible damage to the trees. Heavy infestations can cause stunting of the terminal leaves. Dormant or summer oils may be effective in killing the scales, as well as contact insecticides applied when the first instar crawlers are present. A systemic applied to the trunk or soil may also be effective as the scales ingest the material, and this will provide a much longer residual effect in the foliage. The application of a labeled IGR also may be effective if timed for the presence of the crawlers.
