Origin:
Native to the mountains of Mexico, but now present in several states in the U.S., including California and Pennsylvania, and north into western Canada. It also is found in Australia.
Biology:
The preferred host of this scale is walnut, and it is the most important soft scale pest of walnut in California, but it also attacks a great many other trees and shrubs, including stone fruits, pistachio, apple and pear, locust, grape, rose, elm, birch, laurel, sycamore, raspberry, and others. It overwinters as a nymph on small twigs, resuming its growth and change to the adult stage in the spring. While feeding it produces large amounts of dripping honeydew and the resultant sooty mold. The female produces large numbers of eggs in late spring and dies afterward. The mobile crawlers then move to the foliage to feed on the undersides of the leaves throughout the summer, molting to the next nymph stage which then moves back to the twigs for the winter.
Identification:
Mature females are large, oval, dark brown, and with a very distinctive coating of powdery white wax over the entire wax shell. It is very similar to the European Fruit Lecanium scale, which differs by not having the powdery coating of white wax.
Characteristicts Important to Control:
For ornamentals dormant or summer oils may be effective in killing the scales, as well as contact insecticides applied when the first instar crawlers are present. An IGR applied when crawlers are present also may be effective. A systemic applied to the soil can also provide effectiveness in killing the feeding scales. For food-bearing trees a registered insecticide needs to be used as a topical treatment.
