Insect of the Month - Woolly Elm Aphid / Woolly Apple Aphid

Crops Affected:
Saskatoon berries (WEA/WAA), elm (WEA/WAA), apple (WAA), hawthorn (WAA), mountain ash (WAA)

Life Cycle:

• Overwinters as an egg in bark crevices on elm
• 1^st generation (wing-less) feeds on elm leaves
• Winged generation produced in mid-June to mid-July
• Migrate to Saskatoon plants (about 2 weeks after purple lilac blooms) throughout month of July
• Nymphs born upon landing on plants; migrate to roots; rapid population increase
• Colonies found on roots July through October
• Winged generation produced in September and returns to Elm (do not overwinter on roots of Saskatoon)
• Younger, more succulent roots = most susceptible to infestation; 2^nd & 3^rd growing season

• Above ground
  • Lack of vigour in young plants
  • Failure to leaf out or partial leafing out, followed by early season plant death
  • Early/premature fall colour change (late July/early August)
• Below ground
  • White, woolly masses on plant roots
    • Typically found late in the year of infestation or in the following year
  • Infected roots may have a purplish / blue to whitish discolouration
  • Roots may be swollen and puffy
• Presence and damage may not be noticed until after infestation (too late?)
• Symptoms on elm
  • Causes curling of elm leaves
  • Produce copious quantities of honeydew and secrete a powdery white wax

Curled elm leaf, with Woolly Elm Aphid & their honeydew & waxy flocculence evident
Swollen roots and fluffy/woolly residues – indicates a past/present WEA infestation
Photos by Robert Spencer

• Watch for development of above-ground symptoms in spring
• Inspect roots of symptomatic plants by digging a 15cm (6 inch) trench 30cm (12 inches) away from the base of the plant, removing soil from the outside of the trench towards the base of the plant.
• Yellow sticky traps can be used to monitor aphid migration.

• Orthene 75%SP (acephate) application (soil injection) can be made to bearing and non-bearing plants (11 month PHI on bearing plants)
  • Apply mid-July to early August (better as early as possible) – after harvest for bearing plants
• Admire 240F / Alias 240SC (imidacloprid) – soil drench spray application to bearing and non-bearing plants (14 day PHI on bearing plants)
  • Apply early to mid-July – when 75-100% of aphids have migrated
• Avoid planting near American Elm stands