- After 14 years, chloropicrin, Vapam and Vorlex continue to effectively
control internal decay of pressure-treated Douglas-fir
transmission poles, but 6 years after application of methylisothiocyanate
(MIT) some poles are becoming reinfested by decay fungi
although NIT residues remain high in these poles. The closed-tube
bioassay, developed through our research, is an effective method for
detecting fumigant persistance, and future studies will aim at determining
the actual fumigant concentrations detected in wood by this
A study of MIT movement through Douglas-fir pole sections
following treatment with gelatin encapsulated MIT was completed and
results indicate that addition of small quantities of water along with
the capsules will give excellent fumigant release and movement into
the wood. Decay fungi were virtually eliminated from in service
transmission poles 21 months after treatment with gelatin encapsulated
MIT near the groundline. In poles treated up to 12 feet
above the groundline with encapsulated MIT and chloropicrin, no decay
fungi could be isolated 1 year after treatment. Both fumigants were
well distributed through the poles and appear to have moved laterally
from the treatment holes.
One of the goals of our research has been eventual fumigant
application to poles at the treatment plant shortly after conventional
preservative treatments. This would provide predrilled holes for
later fumigant retreatment and would effectively protect the entire
cross section. While the most economical application method
would involve incorporating the fumigant treatment holes into the conventional
predrilling process, it would also result in preservative
treated fumigant holes. Consequently we have initiated studies to
determine the influence of creosote and pentachlorophenol on fumigant
movement into treated wood. Preliminary results indicate that
creosote and P-9 penta base oil slow movement of MIT into wood but do
not prevent the build up of fungitoxic concentrations in the wood.
The new, pelletized MIT formulation has been evaluated in our
laboratory assay for wood fumigants. The results indicate that pelletized
MIT is as effective as pure MIT on an active ingredient basis.
Since pelletized MIT has many similar application and safety advantages
as encapsulated MIT, we intend to further evaluate pellets in
poles in service.
Cedar Sapwood Decay Control
The effectiveness of seventeen chemicals (3 oil-borne, 14
water-borne) for controlling above-ground decay of cedar sapwood was
evaluated using a modified soil block test and an Aspergillus
bioassay. Pentachlorophenol (10%) in diesel oil, currently used for
protecting cedar poles, was markedly superior to all other chemicals
evaluated probably because of the increased penetrability of the oil,
since penta in water at the same strength did not perform as well.
Three other formulations, copper-8-quinolinolate (oil), pentachlorophenol
(2% in water), and 3-iodo propynyl butyl carbamate (2% in
water), exhibited some residual effectiveness; however, more time is
necessary to determine if these chemicals will remain effective. An
additional five chemicals will be evaluated this coming spring.
The persistence of chloropicrin 5 years after treatment in
western redcedar was also evaluated using open tube bioassays, closetube
bioassays and gas chromatographic determinations. The open tube
bioassay indicated that chioropicrin still effectively limited growth
of the assay fungus, P. placenta. Similarly, closed tube bioassays
indicated strong inhibition in the pole interior and lower inhibitions
near the surface. Extraction/gas chromatographic procedures detected
chloropicrin in all cores examined with the highest concentrations
towards the pole interior. Chioropicrin concentration did not correlate
with closed tube results, suggesting that these tests are
measuring different fumigant properties. The results indicate that
chloropicrin should be an effective treatment for preventing cedarbutt
rot and may provide some protection to pole sapwood.
Control poles for the bolt hole protection study were again
sampled and insufficient decay was found in these poles to warrant
evaluation of the various decay prevention treatments. We will reevaluate
the control poles this summer.
Detecting decay and estimating residual strength in poles
An infrared spectrophotometric method of analyzing warm water
extracts of decayed and non-decay wood was evaluated with a number of
brown and white rot fungi. Brown rot was highly correlated with
absorption peaks produced at wavelength 17201cm. Work is now underway
to identify this peak to determine if less involved detection methods
might be employed.
Fluorescent labeled lectins, which have high specificity for
selected carbohydrates, were also evaluated as potential fungal indicators.
Of the lectins tested, wheat germ agglutinin appears the most
promising since it strongly reacted with chitin in the fungal cell
wall, making decay hyphae visible at very early stages of decay.
Evaluation of Douglas-fir beams air-seasoned for 1 or 2 years
using Pilodyn pin penetration, longitudinal compression, radial
compression, bending and culturing indicated that, while there is a
well established fungal flora in the wood, this flora has not yet
affected strength. These tests will be performed on the 3 year airseasoned
beams this coming year. Of the strength tests employed,
longitudinal compression appears promising for estimating pole bending
strength and we intend to further evaluate this method.
As a second phase of this evaluation, the effect of moisture content
on Pilodyn pin penetration was examined. This information is
necessary since pin penetration varies with moisture content and must
be corrected to compare values from different poles. Pin penetration
increased with increasing moisture content up to fiber saturation
and stabilized above this point. The moisture content at 0.5 inches
was highly correlated with pin penetration, and this depth might be a
convenient standard measuring point.
En a new phase of the project, preliminary acoustic testing was
begun using small beams from poles at varying stages of decay. These
beams were sonically evaluated and then loaded to failure in three
point bending tests. Sonic evaluation was highly correlated with NOR;
however, much more testing will be necessary before such an apparatus
can be applied to posts or poles.
Initiation of decay in Douglas-fir poles prior to pressure treatment
The ability of basidiomycetes isolated from air-seasoning poles
to reduce wood strength was evaluated in rapid tests for toughness by
impact bending and changes in the breaking radius of Douglas-fir test
wafers. Although some fungi behaved differently in the two tests,
the test correlations were relatively high (r2 = O.78S). Of 26 basidiomycetous
species evaluated, Poria placenta, P. carbonica, P.
xantha and Crustoderma dryinum most rapidly decayed Douglas-fir heartwood,
but at least one isolate of most of the other species tested
significantly reduced toughness. While the wood decaying ability of
each fungus is important, the frequency of isolation also must be
considered when determining the overall importance of a species.
To determine the influence of wood temperature and moisture content
on establishment of P. carbonica in Douglas-fir heartwood, a
method was developed for direct observation of germinating spores on
wood. In this test, chiamydospores and basidiospores failed to germinate
or colonize wood at moisture content below fiber saturation
suggesting that free water is necessary for infection. Chiamydospores
germinated most readily and colonized wood at 22°C, while germination
was significantly lower and the fungus failed to become established
in wood at 5 or 35°C. Similar temperature responses were obtained
with basidiospores although these spores failed to germinate at 5 and
35°C. Nevertheless, basidiospores may remain viable and retain the
potential to establish colonies once conditions become more favorable.
Exposure of sterilized pole sections at four Pacific Northwest
air-seasoning sites for successive 3-month periods showed a significant
increase in basidiomycete isolation frequency for the period
Nov. '81-Jan.'82. Furthermore, the frequency increased from the
northern to the southern most site. Detailed study of the site
weather patterns strongly suggests that increased basidiomycetous
infection can be related to number of days with measurable rain fall
and temperatures conducive to fungal growth. During the other
periods studied, temperature or precipitation conditions were unfavorable
for infection and pole section moisture contents fell
below fiber saturation. This in turn limited spore germination and
fungal colonization of the wood.
About 30 different basidiomycetous species have been identified
from isolates cultured from sterilized pole sections exposed at the
four sites. In general, the species were the same as those isolated
form air-seasoning poles although there were some significant differences
between the species obtained from the different sites. The
frequency of P. placenta mono- and dikaryons was particularly high with
monokaryons more abundant at three of the four locations. Individual
species exhibited distinct colonization patterns from different pole
zones. For example, P. placenta was isolated most frequently from
heartwood exposed at the pole ends while Peniophora spp. and
llaemotostereum sanguinolentum were recovered most frequently from the
upper surfaces of the pole sections.
Preventing infection of poles by decay fungi during air-seasoning
Pole sections treated with ammonium bifluoride (NH4HF2) or gelatin
encapsulated MIT and chioropicrin were extensively sampled after
air seasoning to determine the influence of these chemicals on wood
colonization by decay fungi. Preliminary results indicate that after
2 years NH4HF2 and the fumigants significantly reduced basidiomycetous
colonization of sterile wood.
Poles treated with Vapam 14 years ago were extensively cored,
the cores were cultured and the resulting fungi were identified to
evaluate the fungal flora of fumigant treated wood. A well developed
fungal flora was identified that differed from that found in nonfumigant
treated wood. These fungi will be further evaluated to
determine their role in fumigant effectiveness.