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Pest Information

Wooly elm aphid

  • Latin Name: Eriosoma americanum
  • Common Name: Wooly elm aphid
  • Other Names: N/A

Pest Details


A native species in eastern North America, and found wherever trees such as Saskatoon (= Juneberry, Serviceberry, wild plum) and American Elm are grown.


These aphids are very similar in appearance and habits to the Woolly Apple Aphid, attaching themselves to the thin bark of twigs or roots to suck plant fluids. The effect on the plant is to cause swollen and knotted areas that may lead to the death of that twig or root beyond the feeding site. In colder regions they overwinter as eggs or nymphs and in warmer areas may overwinter on the bark as mature females. Eggs are deposited in the fall and hatch in early spring, and after 2 generations on a plant winged forms are produced that may then migrate to other nearby plants. Damage to foliage is also seen as badly twisted individual leaves.


The aphids themselves are small and purplish in color, but usually covered with a dense layer of cottony white wax.

Characteristicts Important to Control:

A mature group of woolly aphids has enough wax to repel light mistings of insecticide, so either a powerful spray or the addition of a wetting agent will be helpful to get the material to the aphids. Treatments early in the spring will be more likely to contact the exposed, susceptible crawlers, and dormant oil applications to the bark can kill overwintering eggs, nymphs, or adult females. Once the aphids are infesting the roots of a plant control is nearly impossible with insecticides.

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