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Thermotolerant mould growth in dehumidifier kilns in New Zealand
1996 - IRG/WP 96-10169
Growth of Aspergillus fumigatus and Paecilomyces variottii is common on wood dried in dehumidifier kilns that operate within a temperature range of 35-55°C. Aspergillus fumigatus causes an unacceptable blue / grey discolouration of the woods surface and prolonged exposure to spores during handling of mouldy wood can cause health problems amongst timber workers. A survey of dehumidifier kiln operators in New Zealand was carried out to ascertain the extent of the problem and investigate control options. Significant growth only occurred if initial wood moisture content was above 80%. Results suggested that this was because high relative humidity (98-100%), for periods in excess of 5 days, was a requirement for extensive and profuse growth to occur. Only 3 of the 26 antisapstain treatments tested using a 3 week laboratory trial gave control of Aspergillus fumigatus at 40°C. Fumigation with 4 ppm (mg/litre of air) of formaldehyde gas controlled growth of Aspergillus fumigatus for periods up to 5 days and a second fumigation was often needed for long drying cycles (> 12 days). It seems likely that growth of thermotolerant moulds became a problem when use of pentachlorophenate as an antisapstain treatment was phased out (1988-89). Laboratory trials showed that this was one of the few fungicides that controlled Aspergillus fumigatus.
R N Wakeling, J G Van der Waals


Weather testing of timber - discoloration
2001 - IRG/WP 01-20221
The brightness and color saturation of the timber were reduced over time. The perception of an increasingly dark color in the timber over time is due to the gradual reduction in brightness. The period from May to September was characterized by the greatest discoloration of all three periods of the year. Because this period has the largest number of sunlight hours, and the timber is subjected to a greater amount of sunlight. Furthermore, the period from May to September coincides with the rainy season in Japan, which adds to the discoloration.
T Toyoda, M Azuma, Y Hikita


Copper-resistant fungi on pressure impregnated wood in Denmark
1994 - IRG/WP 94-10078
The occurence of Amorphotheca resinae Parbery and its asexual stage Cladosporium resinae (Lindau) de Vries on CCA and CCB treated wood has previously been shown. In the autumn 1993 some other blue stain fungi were found on CCP and CCB treated pine timber, such as Ophiostoma minus (Hedgc.) H. and P. Sydow, Ophiostoma pilifera (Fr.) H. and P. Sydow and Ophiostona piceae (Munch) H. and P. Sydow. The absense of arsenic from newly impregnated wood may create improved growth potential for species not previously found on pressure impregnated timber, such as the above-mentioned.
J Bech-Andersen, S A Elborne


Photo-discoloration and Degradation of Wood and its Stabilisation by Modification with Benzoyl Chloride
2004 - IRG/WP 04-40274
Photo degradation of Pinus roxburghii (chir pine) and Hevea brasiliensis (rubber wood) was studied under artificial accelerated weathering conditions in a Xenon test chamber. The irradiated samples were analyzed for color changes and chemical changes. Analysis of colour changes in wood surfaces by UV-Vis. irradiation was carried out using a colour measuring (CIELAB) system and chemical changes were monitored using FTIR and fluorescence spectroscopy. Irradiation modified physical and chemical characteristics of wood surfaces and resulted in rapid colour changes, reduction in lignin content and increased concentration of chromophoric groups on the wood surfaces. Colour changes were correlated with formation of carbonyl groups and lignin decay rate determined by FTIR measurements. Fluorescence emission spectra measured from un-weathered wood shows excitation wavelength dependence. Photo irradiation leads to a rapid reduction in the emission intensity, broadening of spectra and a significant red shift in the emission maximum. Photo stability of wood surfaces esterified with benzoyl chloride was also assessed. The modification was characterized and analyzed by fluorescence and FTIR spectroscopy and photo-stability of modified wood was assessed. Esterification of wood by benzoyl chloride suppressed the colour changes (photo-discoloration) and also reduced the lignin degradation and generation of carbonyl groups on irradiated wood surfaces. Results show esterification of wood with benzoyl chloride was effective at inhibiting photo-degradation of wood polymers.
K K Pandey


Bacterial staining of samba (Triplochiton scleroxylon)
1988 - IRG/WP 1362
Red- and green-stained areas on Samba wood have been tested by IR, X-ray and Neutron Activation Multielement Analysis. No difference could be seen between stained and unstained areas. The red- and green-staining seem to be related to the bacteria Pseudomonas aeruginosa which were isolated from both red- and green-stained areas on the wood surfaces.
K Hansen


Soluble nutrient content in wood and its susceptibility to fungal discoloration and decay in above ground and ground tests
2000 - IRG/WP 00-10336
The objective of this comprehensive study was to reveal the impact of soluble nutrients in wood on its susceptibility to fungal discoloration and decay in various tests, which is important for the test methodology and standardisation. Seven tests were carried out including pure culture above and ground contact tests, above ground field test and laboratory ground contact tests. The samples containing soluble sugars and nitrogen were more susceptible to mould discoloration than those poor in nutrients. A laboratory test with the fungus Penicillium brevicompactum predicted well the moulding tendency of the samples in the consequent field test. The samples rich in nutrients showed an average of 16% of mass loss whereas samples poorer in nutrients were significantly less affected (8-9%) after 120 days of exposure in a soil rich in soft rot fungi. A pure culture test with the soft rot fungus Phialophora mutabilis confirmed the above -mentioned observation. Garden compost, rich in both soft rot fungi and bacteria, caused severe mass loss (40-48%) of the samples after 120 days of exposure, but no difference in the mass losses between the samples rich and those poor in nutrients was measured. The content of nutrients was neither related to the mass loss of samples in a soil rich in brown rot fungi, nor in a pure culture test with the brown rot fungus Postia placenta. The nutrient status of samples as well as the choice of test soil can lead to completely different results and, consequently, conclusions. The results are in favour of taking samples with approximately equal content of soluble nutrients to decrease the variability of test results, e.g., mass losses.
O M Caballero, N Terziev


Discoloration of pressure impregnated wood caused by Amorphotheca resinae
1990 - IRG/WP 1438
Amorphotheca resinae Parbery with the anamorph Cladosporium resinae (Lindau) von Arx & de Vries is a cosmopolitan fungus known from aviation kerosene, hydrocarbon contaminated soil and creosoted timbers. In Denmark it causes heavy discoloration on wood treated with waterborne chromate-containing preservatives e.g. CCA-oxide type. The teleomorph produces small spherical fruitbodies widespread on the wood surface causing a more or less black discoloration, while the numerous, dense, conidial heaps of the anamorph appear as irregular greyish-brownish blotches. A survey has shown that both stages appear on freshly CCA-impregnated wood during outdoor storage on all surfaces except on the ends. Stacking with e.g. 15 mm sticks restrains, but does not prevent the problem, and planed as well as sawn surfaces are attacked. On account of its extreme pH-tolerance (from pH 2-9) and its exceptional tolerance towards copper-chromate fungicides, the spores may germinate and the infection take place shortly after the impregnation, and even before fixation of the preservative is completed. The high capacity to grow on impregnated timber mostly increases the spore-count and hence the infection potential on the storage site. Attempts to use different types of additives or surface treatment with mould specific fungicides have not been entirely successful.
F Rune, A P Koch


Association of contents of nitrogen and sugars in rubberwood (Hevea brasiliensis) clones with susceptibility to sapstain by Botryodiplodia theobromae, Aureobasidium pullulans and Aspergillus niger
1999 - IRG/WP 99-10307
The purpose of this study was to determine if nitrogen and sugar contents in rubberwood from three selected varieties (clones) rubber trees would affect the rate of colonisation by Botryodiplodia theobromae (a tropical sapstain fungus), Aureobasidium pullulans (a temperate sapstain fungus) and Aspergillus niger (a common mould fungus). Sapstain growth was rated daily until at least 50% mycelial coverage was achieved for 40x20x5mm3 samples from three rubberwood clones (GT1, PB217 and RRIM600) inoculated with the test fungi and incubated in a humidified petri dish assembly under aseptic conditions. All samples had more than 50% coverage of mycelium after 9 days of incubation. The results indicate that the nitrogen content of clone RRIM600 (1.06lmg/g) was significantly higher when compared to that of clone GTI (0.73mg/g) and clone PB217 (0.78mg/g). After oven drying (45°C), clone PB217 contained significantly higher amounts of fructose (5.55mg/g), glucose (2.30mg/g) and total sugar (13.15mg/g), as compared to clone GTI and RRIM600. Clone GTI had the lowest fructose (0.23mg/g), glucose (0.14mg/g), sucrose (2.20mg/g) and total free sugar (2.56mg/g). RRIM600 however had the highest amount of sucrose. B. theobromae spread significantly faster on RRIM600 (4.3 days when >50% mycelial coverage is achieved) than PB217 (5.6 days) or GTI (5.8 days) which is associated with the overall higher nutrient availability in clone RRIM600. Light sanding (down to 1-2mm depth) of sapstain infected samples revealed that deep sapstain typical of B. theobromae remained in the wood, contrasting with the absence of stain by A. pullulans and A. niger (both are typical superficial stainers) in the sanded material.
A J Ashari, J W Palfreyman, A H H Wong


Destaining wood sapstains caused by Ceratocystis coerulescens
1996 - IRG/WP 96-10159
Fungal sapstain does not reduce the strength of wood, but it does discolor the wood, detracting from its appearance and decreasing the value of wood and wood products. The purpose of this investigation was to assess whether wood sapstain caused by Ceratocystis coerulescens could be destained and existing growth eradicated. The hydroxyl radicals generation under optimized conditions destained the sapstain on southern yellow pine veener disks caused by Ceratocystis coerulescens and killed the existing growth of sapstain fungi. Results indicate that the sapstain, melaninlike pigments of hyphae in pine disks, was destained and the existing growth of Ceratocystis coerulescens (Munch) Bakeshi [C-262] eliminated. As a result, sapstained wood and wood products with sapstain fungi can be salvaged, thus expanding our supply of usable wood.
S C Croan


The natural durability assessments of secondary timber species - field trials
1998 - IRG/WP 98-10297
Secondary or 'alternative' hardwood timber species can replace traditional hardwoods and contribute significantly to satisfying the overall demand for hardwoods in the UK timber market. A selection of these 'alternative' hardwoods is currently being tested at BRE-WTC for natural durability both in ground contact (to EN252) at two field sites, and out of ground contact (as L-joints to EN330) at one site. The objective is to provide an assessment of the suitability of each species for future commercial application. Moisture movement has been monitored in the L-joint tenons showing in less durable timbers, such as rubberwood (Hevea brasiliensis), rapid in-depth wetting during rain. Other monitored features of timber failure in out-of-ground exposure, including surface mould, cracking, discoloration and rot, indicate to date clear species-based differences. Comparison of the test timbers, based upon responsiveness to moisture and degree of timber failure, classify calophyllum (Calophyllum spp.), Ghanaian teak (Tectona grandis) and niové (Staudtia stipitata) as most durable and least reactive to moisture. The results to date of the ground contact trials, when compared with archived durability data show that the archive records of ground contact natural durability remain valid, although some modern plantation-grown timbers, such as teak (Tectona grandis), appear less durable than material from virgin forest. The likely value and commercial application of some of the secondary hardwood timbers examined is summarised.
E D Suttie, R J Orsler


Fungi causing sap stain in wood
1980 - IRG/WP 199
The present paper is a revised edition of former Document No: IRG/WP/125. It contains some additions and an explanation of terminology, as was suggested at a previous meeting of the Group. The paper is a compilation based mainly on available literature. Some of my own unpublished results have been added together with other unpublished data which have been received from the Bundesanstalt für Materialprüfung in Berlin and from colleagues at the Department of Forest Products, Swedish University of Agricultural Sciences, which are acknowledged with thanks. Fungi, described in the text, have been selected according to the following principles: a) the most common and important blue stain fungi, b) less common fungi which have been found in several countries or on several host trees, c) fungi which seem to be of minor interest as blue stain fungi, but which have been used recently in experimental work considering their physiological characters, susceptibility for toxic substances etc. The author regrets that this paper does not cover the tropical fungi, as there have been only a few notes about these in reviews and as the original papers have not been available to our library.
A Käärik


Microscopic analysis of southern pine utility pole core segments
1992 - IRG/WP 92-1542
Fifteen macroscopic core descriptive categories were evaluated by microscopic analysis for accuracy in detecting decay and judging decay severity. Five categories were good indicators of decay as decay was detected in 28 of 48 samples. Five categories were possible indicators of early decay as decay was detected in 6 of 40 core segments and an additional 18 contained hyphae. The remaining five categories were considered indicators of sound wood as no decay was detected in those samples. Macroscopic features which frequently indicated decay were compaction and discoloration. However, discoloration was often misjudged or confused with preservative treatment. Identification of fungal isolates will add valuable information. Thirty-four of 152 core segments from fifteen southern pine utility poles contain soft rot (25), white rot (3) or both (6). Decay detection was improved by using the fiber suspension technique. Soft rot was detected from 1 foot below to 4 feet above groundline and as deep as 15 cm from the pole surface.
S E Anagnost, C J K Wang, M Wright


Log fumigation prevents enzyme-mediated sapwood discolorations in hardwoods
1993 - IRG/WP 93-10003
Non-microbial sapwood discolorations in hardwood lumber can cause economic loss by degrade of quality. Based on the hypothesis that the enzyme-mediated sapstain may develop in part from byproducts of parenchyma cells in wood, reshly felled logs of red oak (Quercus spp.) and sugar hackberry (Celtis laevigata) were fumigated under a plastic tarp with methyl bromide. Log sections were checked after fumigation using triphenyl tetrazolium dye to confirm death of parenchyma cells. Logs were cut into lumber which was bulk-stacked in warm, humid conditions to promote non-microbial stain in the sapwood. Lumber from those logs untarped or tarped but not fumigated developed heavy levels of sapstain whereas lumber from fumigated logs was free of stain. This novel approach is being investigated for prevention of other non-fungal stain in wood (eg. brown stain in softwood) with inclusion of alternate fumigants.
E L Schmidt, T L Amburgey


Recommendations for handling of mold infestation of wooden artifacts
2012 - IRG/WP 12-10790
The presentation gives an overview of the handling of wooden artifacts with mold infestation. The causes of mold deterioration are demonstrated by investigations in a church, a historic library and a monastery in Germany. Investigated infested wooden artifacts were altars, sculptures, picture frames and sarcophagi. Important investigation methods including indoor climate measurement, material and air sampling, microscopy, lab investigations and determination of the mold species are described. The most typical mold species are discussed. Whereas various species of Penicillium are typical fungi, found after water injuries (condensation, leakage, flood), these fungi were not often found in wooden artifacts. Instead, for example, Trichoderma sp. and Aureobasidium sp. were frequently detected on the materials and caused discoloration. Contemporary measures for disinfection and protection of both wooden artifacts and the health of the restorers are shown by examples. Problems are discussed and possibilities for the removal of molds and material preservation by chemicals are shown.
K Plaschkies, B Weiss, W Scheiding


System treatments of Pinus sylvestris - influence on moisture, decay and discoloration
2013 - IRG/WP 13-30612
Biological activity can cause challenges for the use of wood in outdoor exposure. Decay and discolouring fungi influence the service life of wooden constructions, and the moisture content of the wood is often an important factor. The aim of this study was to evaluate the performance of different combinations of preservative/modified wood protection treatments and surface treatments for wooden decks in different exposure situations after ten years of field testing. Fourteen different wood protection treatments were tested, in addition to Scots pine sapwood, Scots pine heartwood and European larch heartwood. Furthermore two different surface treatments were included (alkyd oil with iron oxide pigments (AO) and alkyd emulsion without pigments (AE)) in addition to no surface treatment. The test setup used was the “Stapelbädds metoden”. The bottom layer is in soil contact and this stack method provides a moisture gradient within the five layers included. As expected a gradient of increasing wood moisture content and fungal decay rating was found from the top layer to the bottom layer of the stack. For samples with no surface treatment the treatments with lowest wood moisture content was Styren, Tanalith E7, Royal with pigment, European larch heartwood and thermal modification. In the stacks without surface treatment Royal with pigment and Gori SC 100 were the only treatments with decay rating ≤ 1 in all layers, while Scots pine sapwood, Scots pine heartwood and UltraWood all had decay ratings > 2 in all layers. AE surface treatment decreased fungal decay in all layers for furfurylation, Scots pine heartwood and Tanalith M. A similar trend including all layers was not found for AO. All treatments were totally covered by discolouring fungi with the exceptions of ACQ 1900 and Scanimp. Among the untreated samples European larch heartwood generally gave the best performance. The results show that moisture content and fungal decay rate can be reduced with the support of a surface treatment, but they also showed that the opposite can also be the case after ten years of field exposure.
A Schabacker, G Alfredsen, L Ross Gobakken, H Militz, P O Flæte


Effectiveness of Copper Indicators in Treated Wood Exposed to Copper Tolerant Fungi
2014 - IRG/WP 14-20554
Wood treated with a copper based wood preservative will typically turn a green color. While the depth of copper penetration can be readily discerned from the green color of the copper it is standard practice in research and commercial treating plants to make use of a color reagent such as Chrome Azurol S, Rubeanic acid or PAN indicator to reveal the penetration more clearly. When copper treated wood is exposed to copper tolerant fungi discoloration of the original green color can occur. Reactivity of the treated wood with the color reagents can also be impaired. In this paper, the effectiveness of copper color indicators in detecting copper in wood attacked by copper tolerant brown rot fungi at early and late stages of decay was evaluated. Neither Chrome Azurol S nor PAN indicator could detect copper in the area where incipient and severe decay took place, even when chemical analysis showed significant levels of copper in these areas. Rubeanic acid was the only indicator which provided positive identification of copper in these samples. An FTIR study demonstrated that the loss of green color in copper treated wood by copper tolerant fungal attack is closely related to the formation of copper oxalate. The finding supports the theory that copper oxalate detoxifies copper and acts as a precursor for decay since a significant amount of copper oxalate was found in the area with discoloration but no visual decay, as well as in the area with severe decay. The results from this study suggest that the ineffectiveness of Chrome Azurol S and PAN indicators may be due to their inability to replace oxalate ion to form the colored complex with copper.
L Jin, K Brown, A Zahora, K Archer


Screening of fastener resistance in contact with untreated wood using different test designs
2016 - IRG/WP 16-30686
The performance of fasteners in wooden constructions is an important aspect especially regarding corrosion resistance. In an early stage corrosion of fasteners in untreated timber becomes often visible as a discoloration on the surface of the timber resulting in bad appearance of the product followed by complaints. In order to develop an accelerated test for the assessment of fastener performance the suitability of six oak and larch test sets were exposed in greenhouse. Visual inspections revealed that discolorations occur in oak based sets in a very short time when fasteners were associated with artificial water traps. As expected minor discoloration occurs in larch test sets compared to oak. Nevertheless the results suggest that the setup “with water trap” could be a useful tool for fastener manufacturers to evaluate the performance fastener coatings in service.
E Melcher, S Wolf, U Cera