Seasonal alert from your MRCA Public Open Space Committee

 Regarding oyster shell scale on cotoneaster hedges

CRAWLER STAGE IS COMING SOON

Residents who own cotoneaster shrubs and hedges should know that the crawler stage is a 10-15 day time frame when oyster shell scale insects which suck the life out of our cotoneaster hedges, come out from underneath their oyster shell shaped armour to crawl around on the woody parts of the host plant.  The crawler stage is the only time when these critters can be killed on contact, but they will NOT be on the leaves; they’ll be on both the tiny and large woody stems, known as canes. 

For do-it-yourself spraying with hort oil in a backpack, hand held pump or hose end sprayer, you will get the best kill rate when the crawlers are at their heaviest infestation on or near June 10.  For the best outcome, drench the woody parts of the hedge with spray multiple times between June 9-15.  Since local hedges will be in full leaf by June 8, it’s helpful to use more pounds per inch force to penetrate spray to the middle of wide, tall, mature hedges.

If you prefer to hire a commercial licensed contractor to spray for you, the product used is likely  permethrin rather than horticultural oil.  Permethrin has a residual effect of about a week for any crawlers which contact sprayed stems, whereas hort oil only eradicates those insects it contacts while spraying  Permethrin is a synthetic chemical insecticide which mimics the natural extracts of the chrysanthemum flower which attack the insect nervous system.