Oystershell Scale

    Oystershell Scale

    Lepidosaphes ulmi

    oystershell scales

    Oystershell scales (U.S. National Collection of Scale Insects Photographs, USDA Agricultural Research Service, Bugwood.org)

    oystershell scales

    Oystershell scale adult and crawlers/nymphs (Whitney Cranshaw, Colorado State University, Bugwood.org)

    oystershell scale damage

    Oystershell scale adults  (Whitney Cranshaw, Colorado State University, Bugwood.org)

    Pest Description

    • females: 1/8 inch; brown to gray; oystershell shaped
    • immatures: crawlers (mobile stage) 3/64 inch; pale yellow; wingless
    • immatures: nymphs (sessile stage) resemble adults, but are smaller
    • scales blend in with bark and can be difficult to see

    Host Plants, Diet & Damage

    • over 128 hosts known; worst on lilac, aspen, ash, cotoneaster, willow, poplar and maple
    • feed on sap from cells of stems and branches
    • bark may become completely encrusted in scales
    • bark splitting may occur
    • dieback may occur on single branches, in clusters, or over entire plants
    • serious infestations can cause tree death

    Biology, Life Cycle & Damaging Life Stage

    • overwinter as eggs under the female’s cap
    • crawlers present from late-May to early-June
    • males and females both form scale coverings and remain stationary; males become mobile during mating
    • one generation per year; two generations in warmer regions
    • nymphs and adults are the damaging stages

    IPM Recommendations

    • Keep trees healthy and stress free.
    • Monitor scale crawlers from early-May to early-June using double sided tape wrapped around twigs.
    • Apply horticultural oil to smother scales or scale crawlers when monitoring indicates crawlers are present.
    • Apply a systemic dinotefuran soil drench, granules or bark band in early-May.
    • Imidacloprid is ineffective against hard scales.

    For more information, see our Oystershell Scale fact sheet.