Rough-hewn logs

Mr Storch offers a perfectly reasonable approach for helping to
ensure that wood brought into displays is not infested with wood
destroying beetles. But, one has to be very good to inspect freshly
cut timber and distinguish between the evidence of beetles that can
and cannot reinfest cut or seasoned lumber. Likewise, examining kiln
dried wood and distinguishing between old and new damage can be very
tricky (even many seasoned--no pun intended--pest control operators
have a tough time determining whether infestations are old or
active).

Certainly of his first three steps the crucial one is to kiln dry
the wood. Kiln drying typically reduces moisture content to between
6 and 12% and, in the process, kills beetles, larva, and eggs that
might be present.

Don't, however, be fooled into thinking that this is sufficient.
Once installed, most wood products (such as logs even inside museum
buildings) will exhibit increased moisture levels as they soak up
water from their surroundings. In the humid southeast they tend to
stabilize at the upper level, probably around 12%.

There are several beetles, primarily the lyctids and bostrichids,
which can be found in wood with moisture levels as low as 6%. Of
course the lyctids only attack hardwoods, although the bostrichids
are more open minded and can be found in both hardwoods and
softwoods (sometimes even in heartwoods). The bostrichids, however,
also tend to prefer higher moisture contents.

There are also three types of powder post beetles and the old house
borer which can reinfest seasoned or kiln dried wood. So, once
installed, even if the wood is free of pests, there is a chance they
will return. That chance, of course, depends on conditions within
the museum and, as Mr. Storch implies, the diligence used to keep
them out.

Institutions which are determined to bring wood products like logs
into their facilities might want to explore the use of a residual
pesticide to prevent (or at least discourage) reinfestations. Since
most preservatives are not suitable for interior use, the most
likely candidate are the borates (such as Bora-Care and Tim-Bor),
which are beginning to be widely used and with very good success. Of
course, we've found that the borates tend to penetrate better when
the wood has a higher moisture content than is typical for freshly
kiln dried materials.

The point that might be worth making is that while general advice
can certainly be offered, its always good to focus the solution on
the particular institution, their particular needs, and their
particular abilities. Some institutions can, as Mr. Storch suggests,
provide continual monitoring. Many, however, can't. As a result,
approaches must be different.

For those that would like a few references on wood destroying
beetles, these are good introductions:  Wood Destroying Insects'
Manual (1986, National Pest Control Association); Determining Active
and Inactive Infestations (n.d., National Pest Control Association);
Exterior Wood in the South: Selection, Applications, and Finishes
(1991, USDA, Forest Service); "Old House Borer Control," Pest
Control Technology, October 1992; "Diagnosis and Management of
Powderpost Beetles," Pest Control Technology, April 1993.

Best,

Michael Trinkley, Ph.D.
Director
Chicora Foundation, Inc.
PO Box 8664
Columbia, SC  29202
803-787-6910

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                  Conservation DistList Instance 11:30
                Distributed: Monday, September 29, 1997
                       Message Id: cdl-11-30-001
                                  ***