Oystershell scale is affecting many cotoneaster hedges throughout the city of Calgary. We have also seen this insect pest affect; apples, mountain ash and hawthorn trees. In most cases if an infested hedge looks like it’s dead or dying, rejuvenation and post application of oil and monitoring are required. Prior to application carefully examine your tree or shrub to identify the target pest or problem. Most spray insecticides are non-selective and will also kill beneficial insects. Dormant oil must be applied early in the spring prior to leaf out. The reason applications must be made while trees and shrubs are dormant is that the product will cause damage to the leaves. Never spray on evergreens as this will cause permanent damage and sometimes discoloration of blue species.
A few exceptions are Pure Spray Green because the product label states that application is safe on leafed out plants, the next exception would be on a cotoneaster hedge that has been freshly rejuvenated. When applying make sure that you coat every portion of the plant until the product begins dripping off of the plant being treated. This assures that you get all of the insect shells covered with the insecticide. Make sure to read and follow the product label and wear appropriate personal protective equipment.
You will need
2 Dial calibrated hose end sprayer +/- $20
3 Horticultural oil or Dormant oil or Pure Spray Green +/-$20
1 Read labels
2 Wear personal protective equipment (plastic dish gloves, eye protection, hat, clothes to cover your skin)
3 Set the dial to 20 on the hose end sprayer and fill it with the oil
4 Thouroughly spray the plant until every portion is covered
5 Continue monitoring pest activity and reapply if required when plants return to a dormant state