Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Bronze Birch Borer
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The
bronze birch borer is a small slender beetle that is slightly less than
1/2-inch in length. Its larva is one of the most devastating pests of
white-barked birches in Ohio. The larval stage feeds just under the bark of
birch trees. When this larval feeding girdles a branch or tree, the result is
sudden wilting and death. This native North American insect occurs on birch
from Newfoundland to British Columbia and south to West Virginia, Ohio,
Colorado, Idaho and Oregon. Plants Attacked The
larvae have been recovered from most birch species but European white birch,
water birch, paper or canoe birch, and yellow birch seem to be the most
preferred hosts. |
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Damage Initial
damage is usually discovered when the top part of a birch tree suddenly wilts
and dies. This happens when a larva girdles one of the upper branches.
Careful examination of branches and the trunk usually reveals raised ridges
or bumps, commonly referred to as "gouting" of the branches. These
are ridges formed when a larval tunnel is closed in by callous tissue of the
tree. Often,
D-shaped holes are found in the bark and these may be stained with rust
colored sap. These holes are emergence holes made by adult beetles. Heavy
attacks and continued reinfestation results in most of the branches dying
from the top down. Eventually the trunk is girdled and the entire tree dies. |
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Description and Life Cycle Adult bronze birch borers are rarely
observed because of their secretive behavior and rapid flight ability. The
adults are slender, dark olive-bronze in color with a. bright green iridescence underneath the wing
covers. Males are usually about 3/8-inch long, while females may reach l/2-inch
in length. Most adults have a short white colored dash on the sides of the
wing covers. The
larva is atypical of most flat-headed borers in having the segment behind the
head only slightly wider than the body. The slender, cream-colored larvae
have two short spines at the tip of the abdomen. Newly hatched larvae are
about 1/16-inch long while mature larvae may be 3/4 to 11/4-inch long and
3/32-inch wide. Adults
generally emerge from mid-May to mid-June in southern Ohio. In northern Ohio,
adults may emerge into late June. Emerging adults leave characteristic D-shaped
holes in the bark. The adults feed on leaf margins for several days before
eggs are laid. Mating and egg laying activity is usually located on the sunny
side of trees. Mated females seek out crevices in the bark, especially around
branch scars. Occasionally eggs are placed under loose flakes of outer bark
or around wounded areas. The oval eggs are creamy white when new but turn
yellowish with time. The hatching larvae burrow through the attached egg
shell directly into the bark within 10 to 14 days. The larvae generally bore
in the cambium area but occasionally move into sapwood. The larvae usually
feed laterally around the branch and tunnel in a zigzag manner. Most larvae
mature by late fall and form elongate pupation cells just beneath the bark.
Farther north, many larvae over winter and take a second year before maturing.
Pre-pupae rest over winter in the pupae cell in a doubled-up position.
Pupation occurs in late April into May. Control Hints As
with most wood boring insects, the bronze birch borer is extremely difficult
to control, especially if an infestation is established. This pest seems to
prefer birches located in unsuitable habitats. Birches generally grow in
shady, cool and moist wooded areas. Thus, when birches are planted as an
accent plant in sunny, dry urban lawns, they are rapidly attacked. Strategy 1: Provide Proper
Habitat for Birch Growth – If a birch is deemed necessary for urban landscape planting,
select shaded and semi-moist areas. Use the north and east sides of
buildings. Proper fertilization and control of aphids and leaf miners will
help keep the birch vigorous and better able to withstand borers. Strategy 2: Use Birches Less
Susceptible to Borers - Though they do not have pure white bark, river birch is quite
resistant to attack and gray birch is moderately resistant. However, gray
birch is very susceptible to leaf miners and river birch is attacked by leaf
aphids. Probably the best species is the Monarch birch which has white bark
on older trees and is only moderately susceptible to leaf miners and aphids. Strategy 3: Preventive or Protectant Insecticide Applications by Calendar Dates - Susceptible birches are
rapidly attacked in sunny areas and generally require regular annual protectant insecticide applications. Protectant
surface sprays are applied to the tree bark so that residual insecticide is
present to kill larvae hatching from eggs.
This must be done before eggs are laid and reapplications are needed
if adults lay eggs over extended periods.
A thorough drenching of the larger branches (1 ½-inch diameter or
larger) and trunk is needed to insure the formation of the insecticide
barrier under loose bark and inside bark cavities – areas where eggs are
usually attached. Systemic
insecticides – sprayed, soil drenched, or injected – are applied to kill
feeding adults and young larvae entering the cambium area. Strategy 4: Systemic
Insecticide Application to Control Active Borers - This technique may reduce
damage but often considerable damage has already occurred. True phloem/xylem flowable
systemics may be applied – sprayed, soil drenched,
or injected. |
Information obtained through the Ohio State Extension Factsheet HYG-20 18-95
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES