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

  Hort Snacks - June 2018
Download 358K pdf file ("HortSnacks-June2018.pdf")PDF
     Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
     Hort Snacks HomeHort Snacks Home
 Eriosoma americanum / E. lanigerum

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
  • 1st 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; 2nd & 3rd 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
Woolly Elm Aphid - Youtube video
Share via
For more information about the content of this document, contact Robert Spencer.
This information published to the web on May 29, 2018.