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Cottony Ash Psyllid


The cottony ash psyllid, sometimes abbreviated to CAP, is a small winged insect considered invasive by the Saskatchewan Invasive Species Council. It feeds on the leaves of Manchurian (mancana) and black ash trees as well as their hybrids. During outbreaks, the feeding damage can be severe enough to cause significant dieback or even death in stressed trees.

Signs and symptoms of cottony ash psyllid include:

  • curled, distorted leaves
  • sticky, white substance on the underside of the leaves
  • sticky surfaces below the tree
  • reduced number of leaves on the inner branches

Homeowners should reduce stress on susceptible trees by watering deeply during hot, dry weather, reducing other pests, not using herbicides underneath the tree, and preventing trunk and root damage.

Trees with cottony ash psyllid may be sprayed with insecticidal soap or an insecticide registered for use on trees at bud break, approximately the first week of June, or at the emergence of adult psyllids in July. Spring insecticide treatments are most effective, but summer treatments are useful to protect leaves that have not yet been distorted. Always read and follow label directions when applying a pesticide or hire a professional applicator.

More information and photos of cottony ash psyllid damage can be found at:

For more information, contact the Parks & Recreation Department here or phone (306) 694-4447.

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