Oyster Shell Spraying Starts Today June 7th!

Hello Mount Royal Residents!

In recent years the City of Calgary has had an increasing problem with oyster shell scale (Lepidosaphes ulmiect). This insect is not native to North America and can decimate cotoneaster hedges and other species such as fruit trees, lilac, dogwood, maple, poplar, and willows. 

MRCA invites everyone to learn more about the invasive oyster shell scale in hopes of protecting our community  hedges and trees.

Treatment is highly time specific. The only opportunity to kill the scale insects on contact with smothering oil is the two week long crawler stage, right after they hatch.

What you can do

Over the next ten days or so (approximately June 7th-June 17th, 2021) apply a heavy spray of oil and water mixture to the stems and canes of your cotoneaster plants. This insect will be on the woody parts, not the leaves.  Unless you have a high pressure sprayer, it’s difficult to hit enough insects to achieve control with a single spray, so try to spray 2-3 times over the ten day period.  Most folks use horticultural oil because it’s cheap and effective when mixed according to instructions on the bottle.  Certainly, other oils (linseed, neem) have been used, but hort oil is easy.

Since the City of Calgary is not currently treating for scale on boulevard cotoneaster, you are wise to spray nearby cotoneaster to prevent spread to your private property shrubs.

More resources:

The City of Calgary Oystershell Scale

CBC News “Oystershell scale spreading through Calgary hedges”