Oystershell Scale (Lepidosaphes ulmi)
Figure 1. Oystershell scale adult and eggs. Photo by W. Cranshaw, Bugwood.
Figure 2. Oystershell scale infestation on the trunk of an aspen tree. Photo by W. Ciesla, FHMI, Bugwood.
Hosts
Aspen, ash, cotoneaster, willow, and lilac
Damage and Symptoms
Branch dieback can occur with heavy infestations.
Life Cycle
Eggs hatch around mid-late May. The crawlers then feed, settle, mate, and produce an armored shell on branches for overwintering. The female produces eggs and remains protected underneath the shell throughout the winter.
Management
In small numbers, oystershell scale rarely affects plant health. The scale is typically controlled by natural enemies later in the season. If practical, scrub the branches lightly with a plastic brush. If chemical control is necessary, apply a dormant oil before bud break. Monitor for the crawler stage and follow up with a contact spray if populations are heavy.
Figure 3. Oystershell scale eggs. Photo by W. Cranshaw, CSU, Bugwood.
Further Information
To learn more about the topics discussed on this page, contact MSU Extension arthropod diagnostician Dr. Laurie Kerzicnik. If you suspect an infestation on your property, contact your local extension agent, the Schutter Diagnostic Lab at Montana State University, or the Montana Department of Agriculture.
This fact sheet is also available as a printable PDF (419KB).
Disclaimer: These recommendations are provided only as a guide. It is always the pesticide applicator’s responsibility, by law, to read and follow all current label directions for the specific pesticide being used. The authors and Montana State University assume no liability resulting from the use of these recommendations. The Montana State University Extension Service is an ADA/ EO/AA/Veteran’s Preference Employer and Provider of Educational Outreach.