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Wood boring beetles fall into two major categories, those that infest
only live trees or recently harvested wood and those that infest dry,
seasoned wood. For all practical purposes, it is not necessary to treat wood
for beetles such as round head borers, flat head borers, ambrosia beetles,
or bark beetles since they will not re-infest dead wood. However, emergence
holes on exterior surfaces should always be filled to prevent water from
penetrating into the wood, causing decay.
Anobiid Beetles
The most commonly encountered wood boring beetle infestation is caused by
the anobiid beetle. Although often called a "powder-post" beetle, it is not
a true a powder-post or lyctid beetle. One reason for its widespread
presence is its ability to infest both hardwoods and softwoods. Since most
modern construction uses spruce, pine, and fir softwood species, wood
members such as floor joists, beams, sills, and studs are susceptible to
attack by anobiid beetles. Most infestations start in crawl spaces or other
moist areas then move to other sections of the home. Since most infestations
develop rather slowly, damage is usually detected in homes older than ten
years.
Fine sawdust or frass coming out of small holes in the wood is typically
the first sign of the presence of anobiid beetles. The frass has a gritty
feel to it as opposed to the talcum powder consistency of lyctid beetle
frass. One of the challenges when dealing with an anobiid beetle infestation
is the determination of whether the infestation is active or old. A good
method is to cover a six-inch area of suspect wood with one layer of masking
tape in early to late spring. If after a couple of weeks there are no small
holes in the masking tape the chances are that the infestation is old and
inactive.
TREATMENTS
Treatments for anobiid beetles should always start with moisture control.
Anobiid beetles prefer moist wood and high moisture levels shorten their
life cycle and speed the development of the infestation.
The most effective chemical treatment is the application of borates such
as Shell-Guard and Armor-Guard. These products make the wood toxic to the
developing beetle larvae and prevent newly laid eggs from hatching. Usually
it takes from two to three months to eliminate an anobiid beetle
infestation. We recommend the use of Shell-Guard® for treating active
infestations and Armor-Guard® for protecting un-infested wood from future
attack.
Lyctid Beetles
The true powder-post or lyctid beetle attacks only hardwoods such as oak,
ash, hickory, walnut, and mahogany. Infestations are most likely to occur in
hardwood flooring and paneling. Other common infestation sites include
bamboo furniture and trim and picture frames made from tropical hardwoods.
Like anobiid beetles, the first sign of an infestation is usually fine
talcum powder-like frass coming out of tiny round holes in the wood. Another
indicator is the presence of small, elongated black beetles on windowsills
and other surfaces.
Lyctid beetles are typically introduced into a home as eggs or larvae in
firewood or in new molding that has been improperly stored or dried. They
have a relatively short life cycle and an infestation can spread to
unpainted wood surfaces within a year or two. The female lays her eggs in
the pores of the wood and if these pores are filled with a paint or stain,
the wood will not be susceptible to infestation.
TREATMENTS
Treating for lyctid beetles is similar to treating an anobiid beetle
infestation. Lyctid beetles are particularly sensitive to borates and both
Armor-Guard and Shell-Guard will eliminate an existing infestation and
protect the wood from future attack. However, an infestation of lyctid
beetles often becomes evident after the infested wood has been coated with a
finish. For example, infested wood flooring may show no signs of an
infestation until a year or so after it has been installed and finished. In
order to properly treat the floor with a borate it will be necessary to
entirely remove the finish by coarse sanding. Once the floor has sanded and
cleaned the borate (in this case we recommend Shell-Guard because of its
penetrating ability) may be applied. Once dry, the floor may then be fine
sanded and the finish reapplied.
Old House Borers
Old house borers present the greatest control challenge to the pest
management professional. They are large insects with a life cycle that can
extend to 10 or more years. The old house borer attacks only softwoods and
the initial introduction typically occurs while lumber is being stored in a
lumberyard. Although named the old house borer, the first emergence of these
beetles in a home usually appears within five to seven years after
construction.
The earliest indication of an old house borer infestation is usually the
noise made by older larvae chewing in the wood. This can be very
disconcerting to the homeowner, especially in the middle of the night when
larvae are most active. The appearance of oval emergence holes is the next
step in the process. The frass consists of fine powder and small tightly
packed pellets. Like an anobiid beetle infestation, most structural damage
is caused by water infiltrating into exterior emergence holes, thus
promoting decay.
TREATMENTS
Treating a home for old house borers takes some patience on the part of the
homeowner. The only quick remedy is a structural fumigation. However, few
homeowners are willing to bear the cost of fumigation or the inconvenience
of leaving their home for a few days. Borate treatments work but they take
time, sometimes lots of time before total control is achieved. It is not
uncommon for old house borer activity to continue for up to a year and a
half after a borate treatment.
Additional borate treatments will not speed the control process. Since
older beetle larvae are large insects and at that stage of their lives eat
little wood, their tolerance to borates is quite high. They will probably
complete their life cycle and emerge as adult beetles. The presence of
borate in the wood does two things; first it kills younger beetle larvae
that are feeding in the wood, and second it prevents any old house borer
eggs from hatching. Thus, the borate treatment interrupts the beetle's life
cycle and eventually the infestation will end.
Armor-Guard and Shell-Guard
Both Armor-Guard and Shell-Guard are highly effective against wood boring
beetles. We recommend using Shell-Guard for eliminating active infestations
because the glycol components aid the penetration of the borate into the
wood where the beetle larvae are most active. This results in quicker
control. Areas that have been treated with Shell-Guard will also be
protected against future infestations.
Armor-Guard is best used as a preventative measure since it typically
stays near the surface where it prevents beetle eggs from hatching. For
example, if an active infestation of anobiid beetles is found in a crawl
space, we would recommend that Shell-Guard be applied to those areas where
activity is noted and Armor-Guard be applied to the remainder of the crawl
space as a precaution against future infestations.
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