Damage of ash leaflets caused by cottony psyllid
The cottony psyllid (Psyllopsis discrepans) is a recently introduced insect to the Edmonton area, being first discovered here in 2000. Cottony psyllids belong to the family of insects sometimes called jumping plantlice.
Attacks by this psyllid on black ash trees can be very noticeable. Natural control of this insect in our area seems to be largely lacking at this time.
These cottony psyllids attack black and Manchurian ash, but not green ash. These insects suck sap from the leaflets. This feeding causes ash leaflets to become shriveled and discoloured. The leaflets curl under from the sides to enclose the psyllids and a white, cottony material they produce.
What You Can Do
Trees that are kept healthy and in optimum growing conditions are better able to sustain insect attacks. Insecticidal soap is a less toxic product registered for the control of psyllids.
The best time to treat is just after budbreak when the young psyllids hatch. Homeowners also have the option of hiring the services of a certified tree spraying company if a serious outbreak persists.
The City of Edmonton pest management staff found little effect of horticultural oil or dormant oil against overwintering psyllid eggs. Currently the City is assessing insecticide injections on boulevard ash trees.