Oyster shell scale

Credit: Vijay Cavale/Wikipedia

Oyster shell scale (Lepidosaphes ulmi) is normally a sucking rather than a chewing insect.

There can either be one or two generating per season. They overwinter as eggs under female shells and hatch in late May or June, producing young crawlers (juvenile stage) that are quite mobile. As the crawlers eventually settle down, they produce a shell shaped like an oyster shell, hence their common name.

To control this pest, try the following:

  1. Apply a spray during the summer to control the crawlers.
  2. Dormant oil can be used to control adults. Always follow the label directions. Test-spray a small portion of the plant first to check for possible side effects.
  3. Natural predators, such as parasitic wasps, can also help to control the population.