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Shelterbelt Centre Pest Leaflets
Ash Borer
Hosts: Ash and lilac
Appearance and Life History: The ash borer requires two years to
complete its life cycle. The
adult is a
clearwing moth that resembles
a small wasp. Adults are
present from late May to late
July and deposit clusters of
eggs in bark crevices and in
wounds caused by pruning or
previous borer attacks. After
hatching, the larvae bore into
the tree and feed on the inner
wood for almost two years. In
the spring of the third year the
full grown larvae make a
tunnel almost to the exterior,
leaving only a thin covering of
bark. The full grown larvae
are white with reddish-brown
heads and are 18 to 25 mm
long. Just before the adult
emerges the pupa twists and
turns until it breaks the thin
layer of bark. As the adult
emerges, it leaves behind a
pupal skin protruding through
the opening.
Damage: The ash borer
attacks trees of all ages, but
younger, weakened trees are
most susceptible. The insect
causes damage by making 8
mm diameter tunnels that can
extend 100 mm within the
wood. Severely-infested trees
may contain 50 or more borers
that cause weak limbs to break
during high winds. Ash borers
seldom kill trees directly, but
their damage allows other
insects and diseases to enter
the tree.
Control: Wrap burlap around
infested trunks to prevent adult
emergence and egg laying.
Probe active burrows with
flexible wire to kill the larvae.
Remove and burn heavily
infested trees. The insecticide,
chlorpyrifos can be applied to
the lower 3 m of the tree in late
May and again in late June for
control of the ash borer.
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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