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Shelterbelt Centre Pest Leaflets
Elm Aphids
Hosts: American elm
Appearance and Life History:
There are two different species
of aphids that feed on American
elm; woolly elm aphid and
woolly apple aphid. Both
species overwinter in the egg
stage on American elm. As the
buds begin to break, the aphids
emerge and begin feeding on the
developing leaves. Once
mature, the aphids produce a
generation of young. The
feeding action of these aphids
cause the leaves to curl and
develop abnormally. Within the
damaged leaves the aphids
produce two more generations.
By late June, early July the
aphids migrate to their
secondary hosts. Several more
generations of aphids are
produced on the secondary
hosts. In the fall the aphids
migrate back to the American
elm where overwintering eggs
are produced.
Damage: Both species of
aphids cause damage by
sucking sap from the host. The
feeding action of the woolly
apple aphid causes a stunting
and curling of leaves,
forming a rosette-type
deformation. By mid-June, the
host may consist of many
rosettes which appear
extremely unsightly. The
feeding action of the woolly
elm aphid causes the leaves to
swell and curl downward along
the leafs edge. As the woolly
elm aphids continue to feed and
multiply they excrete an
excessive amount of sweet,
sticky substance called
honeydew. The honeydew is
extremely annoying especially
when it covers walks, cars and
other objects under the trees.
Neither species of aphids cause
permanent damage to the elms.
Control: Satisfactory control of
the elm aphids may be achieved
by pruning out and destroying
the aphid-infested leaves.
Control of the aphids can be
achieved by applying
insecticidal soap, malathion or
diazinon just before bud break
and again ten days to two
weeks later.
For more information contact:
PFRA Shelterbelt Centre
Indian Head, Sask. S0G 2K0
Phone: (306) 695-2284 or Fax: (306) 695-2568
E-mail: pfratree@agr.gc.ca
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