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 Curled and Twisted Leaves
Curled, twisted leaves (top) and cottony tufts (bottom)
are the first symptoms of cottony psyllid infestation


Cottony psyllids (Psyllopsis discrepans) are soft-bodied insects closely related to aphids.  Originally from Europe, they have killed thousands of trees in Edmonton since 2000, and were first found in Grande Prairie in August 2015.

Plants Affected

  • Black ash 
  • Manchurian ash
  • Hybrids of black and Manchurian ash


The first generation of cottony psyllid hatches early in spring and enters the bud as soon as it breaks.  They feed on the newly forming leaves, which become twisted, curled and deformed as they emerge.  The nymphs inject a toxin during feeding which contributes to deformation of the new leaves.

The second generation hatches in mid July and feeds on the new leaves that the tree produces after the first generation of psyllids damage or kill the spring leaves.  This combined feeding pressure kills the tree much quicker than pests who only have one generation per year.


Cultural or Non-chemical Controls:

  • Keeping your tree well-watered will help it withstand feeding pressure.

Chemical Controls:

  • Due to the insects being sheltered underneath the curled leaves, tree injection with a registered herbicide is the most effective chemical treatment.
  • The City recommends homeowners contact local tree service companies to ask if they provide tree injection services for privately owned trees.    
     Infested Tree
    Heavy cottony psyllid infestation results in rapid tree
    decline and mortality.

    Last updated: 7/5/2018 10:48:50 AM