Insect Blog

Oystershell Scale

May 14th, 2019

Plants Affected:

Predominantly lilac, ash, poplars, cottonwood, aspen, cotoneaster and to a lesser extent birch, maple, walnut and dogwood.


Oystershell scale is a sucking insect that implants itself into a twig and sucks the nutrients out resulting in a dieback that can be of a general nature throughout the entire plant or limited to certain infested branches.

Life Cycle:

Young crawlers that hatch about mid-June are small white specks that move about for short distances before attaching themselves to a branch.  As they grow, they secrete a hard wax coating over themselves that causes them to resemble a small oystershell about 1/8″ long.  Eggs are laid in the late summer and the scale dies.


Scale is an insect that predominantly attacks stressed plants.  It is advisable to deep root fertilize the infested plants to invigorate them.  Additionally, a yearly spray is timed to coincide with egg hatch that usually occurs in June.  Old, dead scales from previous years do not fall off unless brushed off.  Scale can cause considerable damage and can take up to five years of repeated treatments to control on certain plant species.  Checking for scale on the new growth can aid in determining future spraying needs.