Oystershell Scale

family: diaspididae
species: lepidosaphes ulmi
common names: oystershell scale
hosts: elms, walnuts, ornamentals, fruit and nut trees
notes: Sexual dimorphism (males are elongated)

Agriculture and Agri-Food Canada Insect Identification Sheet No. 9 October l982 Oystershell Scale Lepidosaphes ulmi (Linne) The oystershell scale is a common pest of many fruit trees and brambles throughout Canada. Another species attacks many of our shade trees and shrubs.

Injury:

Small dark-brown scales are found adhering closely to the bark of the trees, appearing much like half of a tiny oyster shell, about 3 mm long. They are usually clustered on the bark; branches of a heavily infested tree may be entirely covered. The tree loses vigor, the foliage is undersized and speckled, and in severe infestations, the tree may die.

Life History:

The insect passes the winter in the egg stage, protected by the waxy cover of the former parent. About 50 to 150 whitish eggs may be found under each shelter. The eggs hatch in late spring, after the trees have bloomed. The tiny nymphs crawl over the bark for a few hours, then insert their beaks into the bark to feed. Soon, a waxy scale-like coating covers their bodies.

The insect becomes fully grown by mid-July after several molts. The mature adult lays eggs under its scale, and as more and more eggs are laid, its body gradually shrinks towards the small end. In mild areas of Canada, a second generation is possible.

Pest Management:

In late spring, when the trees are still semi dormant, spray dormant oil. In heavy infestations spray when the nymphs (crawlers) are emerging. For further information, consult your provincial Department of Agriculture.