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 Shell Thickness Indicator. A shell thickness indicator (Figure 1-5) can be
used to determine the thickness of the non-decayed wood when poles are
drilled rather than using an increment borer.. The rod is inserted into the
hole and then pulled back with pressure against the side of the hole. The
hook at the end will catch on the remaining sound wood.
When pushing a tight fitting shell-thickness indicator into a hole, you can
feel the tip of the hook pass from one growth ring to another in solid wood,
but not in rotten wood.
possible if the strength properties of the wood are to be maintained.
Biological tests are still the most reliable means for detecting early stages
of decay.
Culturing. The early or "invisible" stages of decay can be detected by
culturing in the laboratory the core samples you have collected in the field
using increment borers. Each core is placed in a plastic straw, labeled and
the ends of the straw stapled shut.
The cores are brought to the laboratory and culturing begins within 24
hours.
Insect Identification. It is usually beneficial to identify insects if an infes-
tation has occurred. If field identification is not possible collect the insect,
their boring dust (frass), and a portion of the wood with typical damage,
and consult the cognizant Pest Management Consultant (See Appendix A)
for assistance with identification
Determination of Serviceability. The results of your visual and physical
inspections and lab reports help you determine the serviceability of the
wood member. As the integrity of a wood member is destroyed by biologi-
cal agents, its ability to withstand the load it was designed for is diminished.
As more and more wood is destroyed, the structure becomes weaker. With
poles, the location of the wood that is destroyed is more important then the
amount of wood destroyed. The outer 44% of the pole radius contributes
most (about 80%) of the bending strength. Therefore, decay in the center
of the pole will reduce strength substantially less than if the outer shell is
deteriorated. Decay in the above ground portions of the outer shell of a
well-treated pole is an indication that the pole was decayed before treat-
1-12
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