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Shelterbelt Centre Pest Leaflets
Cankerworm
Hosts: Maple, elm and ash
Appearance and Life History: There
are two species of cankerworm, spring
cankerworm and fall cankerworm. Adult
spring cankerworms emerge and deposit
eggs in late March and throughout April,
whereas fall cankerworm adults emerge
and deposit eggs from late September
throughout October. Adult males are
small-bodied, brownish-grey moths with
a 25 mm wing span, whereas females
are dark brownish-grey, wingless and
12 mm in length. The larvae of both
species emerge in the spring just as the
leaves begin to appear and will feed on
the foliage until mid-June. Full grown
larvae measure 30 mm in length and they
range in color from yellowish-green to
brownish-green to black. The only
means to distinguish cankerworm during
the larval stage is to view the false legs
at the rear of the caterpillar. Spring
cankerworm have two pairs of false legs
compared to three pairs on the fall
cankerworm. When feeding is complete,
the larvae enter the soil where they
remain until they emerge as adults, that
fall or the following spring depending
on the species.
Damage: Cankerworm cause
damage by defoliation during
the larval stage. Initial feeding
causes a shot-hole appearance
in the leaves, but advance
feeding results in the entire
leaf being consumed except
for the main veins. Most trees
will re-leaf within three
weeks after a severe attack.
Trees that are defoliated
several years in a row will
show branch die-back in the
crown area.
Control: If you have a small
number of trees, tree banding
is an effective method for
controlling cankerworm. The
bands are covered with a layer
of sticky adhesive which
prevents the wingless females
from climbing the trees to lay
eggs. For the spring
cankerworm, the bands must
be in place from mid-March to
late April, whereas for the fall
cankerworm, the bands should
be in place from late
September to early November.
Chemical control can be
achieved by using carbaryl or
methoxychlor. A biological
insecticide known as Bacillus
thuringiensis is a safe
alternative to chemical
control.
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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