Lepidosaphes ulmi
Pest description and damage Scale insects are small (less than 0.125 inch in length) soft insects that live beneath waxy scales. These insects are often identified by the shape and size of their scales, the description of adult males and females, immature crawler stage, color of eggs, and host plant preferences. The mature oystershell scale is approximately 0.125 inch in length, with a scale cover that is brown or gray , and usually elongated and slightly curved like an oyster or mussel shell. Oystershell scales are on trunks, branches, and twigs. They occur less frequently on the leaves and fruit. Scale infestations often are limited initially to isolated colonies on single branches or twigs. Newly emerged crawlers look like tiny bright white pimples on the bark.
For biology, life history, monitoring and management
See:
Ash (Fraxinus)-Oystershell scale
Management-chemical control
See Table 1 in: