Miller, Donald J. (Donald James)

Western Dry Kiln Clubs

Western Dry Kiln Clubs. Meeting (31st : 1980)

Undetermined

ScholarsArchive@OSU

BLUE STAIN GROWTH REQUIREMENTS AND SOMERELATED CONTROL PROCEDURESD. J. MillerForest Research LaboratoryOregon State UniversityCorvallis, OregonCharacteristics and Spread of Blue StainBlue stain, found in lumber producing areas throughout theworld, occurs in both hardwoods and softwoods. In the UnitedStates, pines and sweetgum seem most susceptible. Stainingessentially is confined to sapwood. The stain is caused by anumber of particular fungi that preferentially invade moist sap-wood and discolor it as they grow and mature. Like all fungi,they lack chlorophyl, need no sunlight, and cannot synthesizetheir own food. The staining fungi feed mostly on the starch andsugar contents of certain wood cells, particularly ray tissue,but otherwise do little damage to the wood. Consequently, thestrength of blue-stained wood is not reduced significantly exceptin toughness (1), nor are other wood properties including decayresistance, permeability to preservative solutions, equilibriummoisture content, gluability, or paintability much affected (12).The extent and rapidity of staining increase as conditions forfungal growth improve. Under optimum conditions, as during warm,humid weather, staining fungi may penetrate within 48 hours beyondthe depth in wood reached by anti-stain chemical dip treatments(3).The spread of staining fungi through log and lumber storageyards may occur in several ways. Contact of bright lumber withinfected wood allows the fungus to grow directly from board toboard and spread locally within a stack of close-piled greenlumber. Wider distribution of the fungus occurs through infectionof green lumber and logs by bits of the fungi or their spores.The microscopic fragments and spores are easily airborne andcarried about by air currents or, to some extent, by insects.The spores of staining fungi are sensitive to dessication butwill germinate if moisture and temperature are adequate. Highhumidity and temperatures near 70°F at moist wood surfaces notexposed to sunlight and rapid drying are favorable for germina-tion. Spores of a common blue-stain fungus Ceratoc'stis pilifera attained 80 percent germination after 25 hours at 68° to 77°F(2). Fungal spores do not infect air-dry wood surfaces; theyrequire high humidity or, in some cases, a film of water (1).There is evidence that even small differences in relative humiditymay affect both amount and rate of germination of fungal spores(7)Germinated spores produce microscopically fine, root-like,colorless "hyphae" that move deep into the sapwood and spreadrapidly along the grain. As the hyphae mature, they enlarge anddarken. It is the mature, brown-colored hyphae that impart thetypically bluish-grey color to blue-stained wood.8In addition to food obtained from the wood and favorablelevels of temperature and moisture, the invading fungus also needsoxygen in order to grow and cause serious staining. If we examinethese requirements in detail it will become apparent how familiarlog and lumber handling practices may control, or in some casespromote, fungal stains.Moisture and Oxygen RequirementsSapwood of freshly-cut, living trees of most western conifer-ous species, particularly sugar pine and western hemlock, may betemporarily too wet for optimal fungal growth. The reduced airspace and lack of oxygen in saturated wood inhibits growth ofcommon wood-inhabiting fungi. Most western softwoods are saturat-ed when the sapwood moisture content is in a range of about 150 to220 percent, depending on the density of the wood (4). Low-density woods with greater void space, like pines and spruces,need higher moisture contents to attain saturation.As saturated sapwood dries, air spaces in cell cavities en-large and the amount of oxygen eventually becomes adequate forfungal growth. Moist sapwood continues to remain vulnerable toinfection and staining during drying, if other conditions arefavorable, until it reaches fiber saturation point. At that time,the moisture content limits fungal growth. Growth ceases whenmoisture content falls to about 24 percent. Further drying to 20percent allows a safe margin beyond what is generally regarded asa no-growth condition.Rapid drying of wood surfaces, or prompt treatment with anantiseptic dip or spray, may prevent new infections, but thesesuperficial treatments will not prevent, interior staining if thefungus has penetrated below the surface into damp corewood.Temperature RequirementsBlue-stain fungi generally grow best when wood temperature isat about 75° to 85°F. Growth is slow and may cease, for practicalpurposes, when the temperature falls below 40°F or rises to 95°For higher. Geographical strains within a species may differ intheir temperature requirements. Some species adjust immediatelyto change in the thermal environment and continue to grow at therate normal for the temperature (3). Their quick response allowsthem to take full advantage of temporarily favorable conditions.Growth and staining are much reduced as temperatures approachfreezing, but the fungus may withstand periods below freezing. Acommon species, Ceratocystis pilifera, which is tolerant of lowtemperatures (2), produced viable spores and stained wood slowlyat 38°F (5).Staining fungi are more sensitive to heat than to cold.Lindgren's work (3) showed that an increase of 9° to 15°F aboveoptimum temperature inhibited growth, whereas a decrease of 36°For more was required to inhibit growth. Growth slows rapidlyas temperature rises above optimum and then practically ceases at-95°F. However, an air temperature of 95°F is not likely to slowfungal growth within the cooler confines of a pile of sappy, greenlumber where both temperature and moisture conditions would appearto be favorable for staining. Artificially high temperatures used9in dry kilns can be lethal, especially under moist conditions.Some blue-stain fungi may withstand 150°F for at least an hour,but a dry-bulb temperature of 150°F held for 24 hours should killboth stain and decay fungi (8).Sprinkling stored logs with water helps to maintain highmoisture content and thereby retard entrance of fungus-supportingoxygen into the log. Slime growth over log ends is encouraged bysprinkling; it does no harm and may help slow oxygen entry (11).Thorough coverage with water sprays of log surfaces, especiallythe ends, is important. Mist nozzles on risers between log decksare more effective than drenching sprays from atop decks forwetting the unevenly projecting log ends (9). Water temperatureis less important than thorough wetting. Volkmann (13) found noserious damage to pine pulpwood stored for a year under sprinkledwarm water (100° to 102°F) from evaporator hot wells. Inter-mittent spray cycles (6 minutes on, <10 minutes off) were aseffective as continuous sprays on pine logs (6). Sprinkling alsocontrols checking and insect attack and can facilitate debarking.Hot logging and milling procedures race against time toreduce exposure during which stain might develop and spread afterfelling and throughout milling and drying. During that sequencethe wood may become infected, but the fungus may not mature enoughto produce serious staining.Drying and Chemical TreatmentsOnce logs have been sawed into lumber and the wood is in aform convenient for drying, prompt drying to a safe low moisturecontent, rather than wetting by sprinkling, is a practical meansfor controlling stain. Otherwise, chemicals may be used to pro-tect lumber that will not be dried soon.Air drying of lumber surfaces quickly below fiber saturationpoint reduces the wood moisture content to levels that do notsupport spore germination or favor fungal growth. Fast surfacedrying lessens the chance of infection, but when drying conditionsare poor, the fungus may move inward ahead of the inhibitingfiber-saturation level and cause interior staining. Stackinggreen lumber in solid piles for a day or two during warm weathercould produce interior staining later during air drying.Kiln drying imposes stresses of both low moisture and hightemperature on fungi unlucky enough to undergo the process. Resi-dent wood-staining fungi will probably be killed by dry-bulbtemperatures of 150°F held for 24 hours. The Dry Kiln Operator'sManual (8) suggests schedules for sterilizing lumber to kill fungiand insects. Kiln-dried lumber is only temporarily sterile, but,like any dry wood, it will remain safe from blue stain as long asits moisture content does not exceed 20 percent. Chemical treat-ment is recommended if insect damage is a danger during laterstorage or use (8).Anti-stain chemicals provide a superficial antise p tic treat-ment that inhibits fungal infection of lumber surfaces. Chemicalsoften are applied by dipping or spraying and are useful for pro-tecting green lumber during temporary storage or export (10). Theyshould be applieL soon after sawing to avoid possible internalstaining. Some species of blue stain fungi may be resistant to1 0particular treatments (2). Your vendor should be able torecommend the formulation and concentration appropriate for yourconditions.SummaryBlue stain fungi have specific requirements for oxygen,moisture, warmth, and food--all of which must be satisfied if thefungi are to thrive and mature sufficiently to cause serious woodstaining. Most stain control procedures used during logging,storage, and milling operations attempt to deprive the fungus ofone or more needs. Hot logging and milling may outstrip thedevelopment of stain. Stored logs that are kept wet maintainhigh moisture contents and thus limit oxygen in the sapwood.Lumber may be quickly dried to deny adequate moisture, or may betreated with antiseptic chemicals if drying must be delayed.Literature Cited1. Boyce, John Shaw. 1948. Forest Pathology. 2nd Ed. McGraw-Hill Book Co., Inc., New York.2. KHHrik, Aino. 1980. Fungi causing sap stain in wood.Sveriges Lantbruksuniversitet, Institutionen (Or virkesrdra,Rapport nr R 114. Upssala, Sweden.3. Lindgren, R. M. 1942. Temperature, moisture, and penetra-tion studies of wood-staining Ceratostomellae in relation totheir control. U.S.D.A. Tech. Bull. No. 807.4. MacLean, J. D. 1952. Effect of moisture changes on theshrinkage, swelling, specific gravity, air or void space,weight and similar properties of wood. U.S. For. Prod. Lab.Mimeo No. 1448.5. Miller, D. J. and B. Goodell. 1980. Blue staining inponderosa pine sapwood at moderate and low temperatures.Manuscript submitted for publication, For. Prod. J.6. Miller, D. J. and Sam Swan. 1980. Blue stain in sprinkledlog decks and lumber piles of ponderosa pine. For. Prod. J.30(2):42-48.7. Morton, H. L. and D. W. French. 1966. Factors affectinggermination of spores of wood-rotting fungi on wood. For.Prod. J. 16(3):25-30.8. Rasmussen, E. F. 1961. Dry kiln operator's manual.U.S.D.A. Agriculture Handbook No. 188.9. Richmond, H. A. and W. W. Nijholt. 1972. Water mistingfor log protection. Pacific Forest Research Centre, 506 W.Burnside Rd., Victoria, B. C.1 110. Roff, J. W., A. J. Cserjesi, and G. W. Swann. 1980. Pre-vention of sap stain and mold in packaged lumber. Tech.Rep. No. 14R. Forintek Canada Corp., Western Forest ProductsLab., Vancouver, B. C. V6T 1X2.11. Scheffer, T. C. 1969. Protecting stored logs and pulpwoodin North America. Material and Organismen 4. Bd. Heft 3.Verlag: Duncker & Humblot, Berlin 41.12. Scheffer, T. C. and R. M. Lindgren. 1940. Stains of sapwoodand sapwood products and their control. U.S.D.A. Tech. Bull.No. 714.13. Volkmann, D. 1966. Water spray storage of southern pinepulpwooc. Tappi 49(7):48A-53A.12

Blue stain growth requirements and some related control procedures

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Blue stain growth requirements and some related control procedures

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