- This fifth annual Cooperative Pole Research Program report
outlines our progress in the six project objectives.
Sampling of previously established field tests revealed that
Vorlex and Chloropicrin continued to perform well after 15 years,
while Vapam was slightly less effective. Solid methylisothiocyanate
(MIT) also performed well in the field after 7 years. In additional
tests, gelatin encapsulated MIT migrated through Douglas-fir heartwood
with addition of moderate quantities of water to degrade the gelatin.
However, in the presence of higher quantities of water or no
additional water, MIT migration into the wood was slowed. In a
previously established test, gelatin encapsulated MIT continues to
inhibit reinfestation of poles 3 years after treatment.
Pelletized MIT is a new formulation (65% active ingredient) that
appears to have some promise. Preliminary tests indicate that up to
95% of the MIT is release in 24 hours, but a small quantity of MIT
remains in the pellets after 63 days aeration and may pose a disposal
The solid MIT formulations will permit aboveground applications,
increasing the risk that MIT will come in contact with pole hardware.
Preliminary tests indicate that MIT had little effect on corrosion of
hot dipped, galvanized bolts attached to wood. This suggests that
treatment in the crossarm zone with MIT or fumigants that produce MIT
should not affect the integrity of attached hardware.
In addition to fumigant evaluations, we recently examined an
earlier test of groundline treatments with Osmoplastic® and
Hollowheart®. After 10 years, these treatments are performing
reasonably well, with only a slight rise in the incidence of decay
fungi in the past 4 years. We also reevaluated the effectiveness of
kerfing for preventing decay and found that this process
reduced the depth and width of checks, resulting in a decreased
incidence of decay fungi. Kerfing appears to be a valuable method for
preventing internal decay at the groundline.
Cedar Sapwood Decay Control
This past year, the second set of five chemicals applied to
control sapwood decay were evaluated after 2 years of exposure. As in
earlier evaluations using the Aspergillus bioassay, none of the
chemicals approach pentachlorophenol in oil for ability to inhibit
sporulation of Aspergillus niger; however, several samples from zones
deep in the wood produced a slight zone of effect. This may indicate
the presence of a reservoir for long-term protection against decay.
Several of the chemicals including Fluor Chrome Arsenic Phenol and
Ammoniacal Copper Arsenate (ACA) appear to bind to the wood and may be
difficult to detect by the bioassay method. We expect to assess the
effectiveness of these treatments using a soil block test.
Investigations of the reliability of the Aspergillus bioassay
under a variety of conditions indicated that quantity of spores, use
of glass or plastic petri dishes, long-term cold storage, and the use
of spray inoculum instead of flooding spores had little influence on
the bioassay results with pentachiorophenol, Tributyl-tinoxide, or
3 iodo propynyl butylcarbamate; however, incubation temperature did
influence assay results. The Aspergillus bioassay is a simple,
effective means for estimating residual preservative levels.
Again this year, wood around the unprotected, control bolt holes
in pole sections contained such low levels of decay fungi that
evaluation of the treated poles will be delayed another year.
In addition to the initial bolt hole treatments, we have begun a
test to determine if gelatin encapsulated or pelletized MIT can
prevent decay development in field-drilled bolt holes. The pole
sections used in these tests had already begun to develop decay prior
to treatment and will provide an ideal test material.
Detecting Decay and Estimatin& Residual Strength of Poles
Fluorescent labeled lectins used in our earlier studies detected
decay fungi at low weight losses under laboratory conditions. We are
currently evaluating this method for detecting fungi in increment
cores removed from poles to reduce the need for culturing.
Last year we identified a peak that was unique to infrared (IR)
spectra of warm water extracts from decayed wood. This past year we
attempted to identify the chemical responsible for this peak and found
that carbonyl compounds, probably from oxidative lignin degradation,
were responsible for the peak. Since brown rot fungi apparently do
not completely metabolize lignin breakdown products, they accumulate
in the decaying wood and can be readily detected by their IR spectra.
Strength properties of beams cut front Douglas-fir pole sections,
air-seasoned for 3 years significantly decreased although decay fungi
could not be uniformly isolated from the beams. In addition, there
were gradual declines in work to maximum load and modulus of
elasticity, as well as increased Pilodyn pin penetration. These
results suggest that some strength losses occurred during
air-seasoning; however, the losses were not large and should not
endanger pole users.
We compared several test methods including the Pilodyn, radial
compression tests, longitudinal compression tests, and the pick test
for evaluating residual pole strength of the wood surface of
Douglas-fir treated with combinations of funtigants or groundline
wraps. The results indicate that only the pick test could accurately
detect surface damage and illustrate the difficulty of detecting
This past year we evaluated several sections cut from ACA treated
poles stored for a number of years to determine if they were worth
salvaging. Static bending tests of beams cut from the ACA treated
zone, the treated/untreated boundary, and the inner heartwood revealed
ACA treated sapwood had lower MOR and longitudinal compression
strength than the other zones. These results represent only a small
sample, but they suggest that some strength loss occurs during ACA
treatments. More importantly, the results suggest that we could have
reliably predicted beam MOR by testing small plugs removed from the
Small beams cut from decaying, pentachlorophenol treated
Douglas-fir poles were acoustically tested for residual wood strength,
then evaluated to failure in static bending. The acoustic test
consisted of sending a pulsed sonic wave into the wood and recording
this wave after it passed through the beam. As it moved, the wave was
altered by the presence of any wood defects or decay, and these
alterations create a "fingerprint" specific for that defect.
Preliminary results indicated that signal analysis was highly
correlated with work to maximum load (r =.82) and MOR (r .88),
suggesting that this approach to decay detection may prove more
reliable than measuring of sound velocity.
Initiation of Decay in Air-Seasoning Douglas-fir
The results of the initial survey to determine the incidence of
decay fungi in poles from widely scattered Pacific Northwest seasoning
yards indicated that a variety of fungi were colonizing the wood.
While most of these fungi do not pose a serious decay problem, two
species, Poria carbonica and Poria placenta, became increasingly
abundant with length of air-seasoning. These fungi are also the most
conunon decayers of Douglas-fir poles in service.
As expected, the number of fungi and the wood volume they occupied
increased with seasoning time; however, this incidence varied
considerably between yards, especially in poles air-seasoned for
shorter time periods. In addition to the variation between sites,
many of the decay fungi colonizing the wood appear to be monokaryons,
indicating that spores landing on the wood are initiating the
The distribution of fungi within the poles indicated that several
of the more abundant decay fungi were present in the outer sapwood
where they would be eliminated by conventional pressure treatment.
The remaining fungi were most abundant in the heartwood but were more
concentrated near the pole end. This suggests that exposed end grain
was more readily invaded than lateral grain exposed in checks.
In addition to identifying the fungi colonizing Douglas-fir, we
examined the effects these fungi had on wood strength. Toughness
tests indicated the presence of wide variation in decay capability of
the isolates. Although there was no consistent pattern, most of the
isolates did not cause substantial decay and, of those that did, only
. carbonica and P. placenta were sufficiently abundant to have a
large influence on wood strength.
Due to the prevalence of P. carbonica and P. placenta in the inner
heartwood, where they might not be eliminated in a short heating
cycle, we evaluated the temperature tolerance of these two fungi in
Douglas-fir heartwood blocks. These tests indicated that both fungi
were eliminated by exposure to temperatures above 71°C for over 1 hour
or 60°C for 2 hours. The results suggest that careful control of
temperature during treatment should eliminate decay fungi and that
wood treated at ambient temperatures should be heated to kill fungi
that become established during air-seasoning.
This past year was the third and final year of the decay
development study. In this study, sterile pole sections have been
exposed for 1, 2, or 3 years at widely scattered Pacific Northwest
sites, then returned to the laboratory and extensively sampled. We
are now in the process of identifying the fungi from the third year
In addition to examining poles prior to preservative treatment, we
are also evaluating poles treated with waterborne chemicals (ACA or
CCA) for the incidence of surface decay. This past year we examined
twenty ACA-treated poles from a line installed in 1946. While a
variety of fungi were cultured from the wood, none of the poles had
evidence of substantial surface deterioration.
A study was initiated on the fungal flora of fumigant treated wood
because of the potential for fungi developing resistance to low levels
of fumigant or the ability to actively degrade the chemical. Both of
these developments could shorten fumigant retreatment cycles and
increase maintenance costs. We have evaluated poles treated 7 and 15
years ago with fumigants and find markedly reduced fungal flora.
Tests are continuing on the fungi isolated, and we hope to assess the
effects of these isolates on long-term fumigant effectiveness.