Insect of the Month - Cottony Ash Psyllid

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