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Questions?
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Beetles & Hardwood
Floors
- How
does
wood
become
infested?
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Summary: Wood flooring can become
infested with damaging beetle larvae when eggs are
laid on unfinished wood surfaces. Hatching
larvae bore into the surface and begin a process
that can result in extensive damage. Even kiln-dried
wood can become infested. Wood flooring can be
protected by sealing the surface and/or treating it
with borate insecticide.
Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
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Wood floor
infestations
There are a number of
insects that develop in recently dead trees or
milled lumber. The larvae of these wood borers feed
on starch and other nutrients in the wood that were
formed when the tree was alive. Most of these
insects, however, cannot infest live trees
because of the tree's natural defenses. While most wood boring
insects need relatively fresh wood, certain ones,
like powderpost beetles, can re-infest older,
seasoned wood.
Powderpost beetles
(see What are
Powderpost Beetles?) lay their eggs on the
bare wood surfaces and tiny beetle larvae (sometimes
called woodworms) bore into the wood through
surface cracks. Extensive internal damage can be
done by the larvae during the months or years in
takes to complete development (see A
Picture of a Lyctid Powderpost Beetle Larva).
Adult beetles emerge through circular emergence
holes (right).
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Round
emergence hole in oak flooring. These
holes often have fine, powdery wood
particles around them. The ruler marks are
1/16" apart.
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Wood may even be infested
even after it has been kiln-dried and milled into
lumber. Infestation occurs when dried wood is
improperly stored near an active infestation (see
below). Kiln-drying alone does not protect
against infestation, it only eliminates larvae that
are present at the time the wood entered the dryer.
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Is the infestation still
active?
This is one of the first
questions usually asked. Since emergence holes are
permanent it is impossible to know for certain if the
infestation is active if you find holes in the floor
as pictured above. The best indication of an active
infestation is the presence of fine, powdery
boring dust associated with emergence holes.
Another good indicator is the condition of the
emergence holes themselves.
Use your hand lens or
magnifying glass to look carefully at the emergence
holes under a good light. If the walls of the hole are
covered with floor finish (below right) you can
conclude that the holes were made before the finish
was applied and may indicate a old, inactive
infestation. On the other hand, if the walls
appear fresh you might conclude that beetles emerged
recently indicating an active infestation.
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Elongated emergence
holes (right) also indicate that the holes were
made before the wood was cut into flooring.
Emergence holes are normally round, elongated holes
occur when a round log is cut at an angle to the
original surface. Another way to distinguish active
from inactive infestations is to mark all existing
holes with a grease pencil so that new ones can
be spotted. You probably won't find beetles flying
around the room.
Control of wood
destroying insects
There are two products
that can be used to protect new floors from wood
destroying insects and fungi. These products are based
on insecticidal borates (see What
are Borate Insecticides?). Bora Care (tm)
(Nisus Corporation) and Shell-Guard (tm)
(Perma-Chink Systems) are glycol-based borate products
while Timbor, also from Nisus Corporation, is
a pure borate powder without any glycol additive.
Timbor is mixed with water to apply. Some studies
indicate that glycol helps to carry the borate into
the wood, other studies found no difference.
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Elongated
emergence holes in oak flooring. These
holes are made when the log is cut at an angle
to the original surface to make flat boards-
indicating that the holes were present
when the wood was milled into lumber.
Note also - floor finish inside holes,
another indication that holes were already
present when floor finished was applied. Ruler
marks are 1/16" apart.
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All borate products
should be applied before wood is stained and sealed
for best results. Bora Care is a 40% solution whereas
Shell-Guard is a 25.3% solution. Keep this difference
in mind when comparing costs. Timbor is cheaper than
either of the glycol-based borates but does not have
the possible benefits of the glycol penetrant.
Borate solution should be
applied to the unfinished back and to
the tongue and groove edges with a small brush or
paint roller. Apply solution to the top only if it is
unfinished. After the solution dries the wood will be
impregnated with borate which will prevent beetle
larvae from boring into the underside, or edges, once
the floor is installed. Don't
get the wood too wet as the flooring may warp. And,
allow it to dry completely before installation. This procedure won't stop
beetles already in the wood floor from emerging but it
will prevent new attacks.
For infestations in existing floors
you'll need to first determine if the infestation is active
(see discussion above). If the infestation is active
see Treating Active Beetle
Infestations in Wood Flooring.
Other Insects That
Damage Wood
What is Timbor
Insecticide?
What are Bora Care
& Shell -Guard?
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Jack DeAngelis,
Ph.D.
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