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University
of Rhode Island GreenShare Factsheets
Dogwood
Borer Synanthedon
scitula (Harris)
Lepidoptera: Sesiidae
The
dogwood borer, which occurs throughout the eastern United States,
is probably the most destructive pest of established flowering dogwood
trees. Young trees may die completely and older trees may be left
with dead or dying branches. Damage by this insect severely limits
the success and attractiveness of dogwood. Borer-infested
trees show swollen, knotty, calloused or gall-like areas on the
trunk. Dogwood borer adults, which are clear-winged moths, make
irregular burrows under the bark on the trunk, especially at ground
level and around the base of limbs or at the edges of wounds or
scars on the bark. Fresh sawdust-like borings are usually present
on the bark near active borer sites. In young trees, the crown is
attacked, resulting in wilting and die-back. Dogwood
borers overwinter as immature larvae (caterpillars) in tunnels under
the bark. Full-grown larvae are 25 mm (1 inch) long and white to
cream in color with reddish-brown heads. Larvae change to pupae
during spring and adults begin to emerge by early June. Adults
are most abundant in July, though some emerge throughout the remainder
of the summer months. Adults are clear-winged moths, active during
daylight hours. They have blue-black bodies with a yellow stripe
on the second and fourth segments of their abdomen; the legs also
have yellow bands. The wings are narrow and transparent. Female
moths lay eggs on smooth or rough bark. On older trees, they lay
eggs in scars and rough areas of bark on the trunk and larger branches.
Caterpillars
hatch in 8 to 10 days and wander around the bark until an opening
is found for their entry into the cambium; the larvae are unable
to chew through bark. Once inside, they are well protected and difficult
to control. Larvae feed in this protected area throughout most of
the year. One generation occurs each year.
Cultural control:
The general prevalence of dogwood borers and the ease with which
they penetrate injured bark makes control difficult. Preventative
control measures include: • Avoid physical
injury to the tree by unnecessary cutting or bruising. Be careful
in use of mowers near the base of trees. • Brace newly
transplanted trees to protect against strong winds. • In some cases,
wrapping the trunks of new trees will reduce egg-laying of
female moths. • Plant non-native
dogwood varieties less susceptible to dogwood decline, since
trees affected by this disease are more likely to be attacked
by dogwood borers. See GreenShare Factsheet on Dogwood
Diseases for more information. • Maintain optimum
growing conditions for trees and remove dead or cankered branches
in dry weather. Chemical
Control: Dogwood
borers are difficult to control once the larvae have gained entry
under the bark of a tree or branch. A residual insecticide applied
in June may help reduce damage and reduce the number of adults which
lay eggs on host trees, but coverage of trees is often expensive
and difficult. Adapted
from the Delaware Cooperative Extension, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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