Cottony ash psyllid

Damaging

Cottony Ash Psyllid (Psyllopsis discrepans)

The cottony ash psyllid is a tiny insect native to southern Europe. It has spread to most of Europe, the UK and more recently, in Canada and the US. It has devastated ash trees in many communities and is listed as an invasive species by the Saskatchewan Invasive Species Council.

The nymph feeds on and damages:

  • Black ash (Fraxinus nigra) and cultivars including ‘Fallgold’, ‘Northern Gem’ and ‘Northern Treasure’.
  • Mancana or Manchurian ash  (Fraxinus mandshurica).
  • It does not infest green ash (Fraxinus pennsylvanica).

Trees under stress from drought or other reasons are most at risk. The psyllids cause dieback over time due to stunted growth of branches and a thinning canopy. As a result, ash trees decline because there is not enough foliage to support the tree. Most trees do not recover from severe infestation and die prematurely.

Symptoms

  • Gnarled, curled or deformed leaflets.
  • Cottony substance found in the curled leaves.

Lifecycle

Tiny, hard-to-see eggs hatch in spring just before bud break. The nymphs pierce the tissue around the buds and suck on plant juices. As the tree leafs out, the tiny nymphs enter the leaf tissue. While feeding, they inject a toxin into the leaf tissue causing it to curl and deform. The second generation of eggs is laid in June and hatch out in July. These nymphs feed within the curled leaves, often secreting a cottony substance. Adults are pale yellow with clear wings and tiny black markings and are 2 – 3 mm in length.

What we know so far:

  • Trunk injections, including neem oil, are being tested but currently there is no evidence to support this approach.
  • It may be difficult for pesticide sprays to access the nymphs inside the leaves, within the curled leaves or protected by the cottony substance.
  • Although natural enemies feed on psyllids, there is no evidence that this will protect the tree.
  • No evidence that dormant oil is effective.

What may help

  • Reduce or eliminate sources of stress.
  • Water your tree deeply (1”) at the root zone once or twice a month until freeze-up.
  • Mulch to conserve moisture. 

Sources

http://www.saskinvasives.ca/index.php?id=14 (Cottony Ash Psyllid Fact Sheet)

https://www.ag.ndsu.edu/pdl/documents/Psyllid_ND.pdf

https://www.ag.ndsu.edu/archive/entomology/ndsucpr/Years/2006/may/4/hort_4may06.htm