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Commonly known as scale insects (Parthenolecanium corni), these pests may be difficult to identify as their appearance varies according to the host. Females are initially flattened and brown in appearance, but become hardened and round as they mature.
Scale Insects

 Mature scale insects on an elm tree.  The mobile
juveniles are visible at the bottom of the picture.

Plants Affected

  • Elm and green ash trees
  • They do not usually pose a risk to local trees unless their population is excessive.


Shiny or slippery looking leaves may be a sign of scale insect presence.  Large populations produce considerable amounts of a sticky substance called honeydew that supports growth of sooty mold.


Apply a dormant oil application to the trunk and branches in early April (before bud break).


Last updated: 9/16/2013 8:09:59 AM