Insect of the Month - Cottony Ash Psyllid

  Hort Snacks - November 2018
Download 533K pdf file ("HortSnacks-Nov2018.pdf")PDF
     Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
     Hort Snacks HomeHort Snacks Home
 Causal Organism: Psyllopsis discrepans

Crops Affected: Select Ash tree species (black, mancana, manchurian, hybrids of black/Manchurian ash, etc.) – not green or white ash

Life Cycle:

  • Aphid-like insect that feeds by piercing and sucking, injecting saliva into the leaf
  • Adults are small (~3mm in length), light green to light yellow with black markings and mostly clear wings (shaded towards tips)
    • At least 2 generations are present each year
  • Eggs overwinter in tight bends (crotches) between twigs and buds
    • Eggs hatch around the time of bud break
    • 2nd generation eggs are laid along the top of the midrib of the leaves
  • Nymphs feed on expanding leaves
    • Nymphs exude a white, waxy substance, leading to the characteristic appearance of “cotton”
    • 2nd generation nymphs feed within the curled/deformed leaves and on other, unaffected leaves
  • Feeding by nymphs causes leaflets to curl along the edge and be deformed – most obvious symptom
    • Leaflets roll under and curl towards the midrib of the leaf
    • Leaflets of ash trees may show browning or yellowing in addition to curling
    • Severe curling is referred to as “cauliflower” appearance
  • White, cottony material may be observed along the midrib of an uncurled leaf
  • Tree crown may appear thinner over time
Cottony ash psyllid adult
Curled / distorted leaves caused by Cottony ash psyllid nymphal feeding
Photo by City of Saskatoon
Photo by City of Edmonton
Photo by City of Saskatoon

  • Monitor trees early for 1st generation nymphal feeding (to allow treatment) and throughout the summer for 2nd generation damage
  • Watch for curling and for cottony material
  • Ensure that trees are kept healthy – ensure good drainage, adequate water and nutrients and freedom from compaction, crowding or other stresses
    • Some literature suggests that watering trees can help to minimize observed damage in trees
      • Control weeds at the base of trees to reduce competition for moisture
      • Bark mulch or other materials can reduce water requirement
  • Control products available for treating trees are limited, particularly in urban and residential situations
    • Some domestic products (e.g. insecticidal soaps) are registered and can be used for control of the pest
    • Treat plants shortly after bud break as the eggs are hatching
    • Treatment later stages (particularly with contact-type products) will be less effective
  • Systemic products are effective but are restricted and not available to everyone
Share via
For more information about the content of this document, contact Robert Spencer.
This information published to the web on October 30, 2018.