Wood Decay, Fungi, Stain and Mold

Transcription

1 Wood Decay, Fungi, Stain and Mold New England Kiln Drying Association Spring 2011 Meeting April 7, 2011 Oneonta, New York Susan E. Anagnost Chair and Associate Professor Department of Sustainable Construction Management and Engineering SUNY College of Environmental Science and Forestry Syracuse, New York 1. The Basics of Wood Decay Wood +Water = Decay 1

2 The process of wood decay requires: 1. Substrate 2. Fungus 3. Moisture Temperature Cellulose Hemicellulose Lignini 2

3 Three Types of Wood Decay Brown rot White rot Soft rot (bacteria) Wood Decay Fungi Brown-rot fungi White-rot fungi Soft-rot fungi Basidiomycetes Basidiomycetes Microfungi : Hyphomycetes Coelomycetes Ascomycetes 3

4 BROWN ROT Consumes cellulose and hemicelluloses Does not attack lignin Results in rapid strength loss 4

5 Brown Rot Cubical rot Cubical pocket rot Dry rot Building rot fungus Cubical pocket rot Incense cedar Postia amara 5

6 Brown Rot of Oak Lenzites trabea Rhizomorphs by the dry rot fungus Meruliporia incrassata 6

7 Mycelial fan by the dry rot fungus Meruliporia incrassata 7

8 Bore holes in Douglas-fir by Poria carbonica Brown rot fungus in Southern pine Hyphae with clamp Hyphae with clamp connections (arrows) 8

9 WHITE ROT Consumes cellulose, hemicelluloses and lignin Some species preferentially attack lignin Results in significant strength loss Pocket rot, stringy rot, spongy rot White pocket rot Ganoderma applanatum 9

10 Simultaneous rot zone lines White rot in a Douglas-fir utility pole after 10 years of service 10

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12 Simultaneous White Rot Cell wall thinning Simultaneous White Rot Trametes versicolor on the lumen surface of a Southern Pine tracheid 12

13 Simultaneous White Rot Bore holes Selective delignification cell separation degradation of the middle lamellae Biopulping Yellow birch by the fungus Mycena leaiana 13

14 Selective delignification cell separation degradation of the middle lamellae Biopulping Yellow birch by the fungus Mycena leaiana SOFT ROT Consumes cellulose, hemicelluloses and lignin Slower degradation than brown or white rot Results in significant strength loss Surface erosion of wood in service 14

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16 Soft rot cavities in southern pine in cross section Soft rot Type 1 Cavities in the S2 cell wall layer 16

17 Soft rot Type 1 Cavities in the S2 cell wall layer 17

18 Soft rot cavity formation Soft rot cavity formation Longitudinal view of chains Longitudinal view of chains of diamond- shaped cavities 18

19 Soft rot Type 1 Diamond cavities in a southern pine tracheid BACTERIA Degradation of submerged wood Conditions of low oxygen 19

20 Erosion bacteria in wooden building support piles From: Nilsson, T. and C. Björdal Identity of wood degrading bacteria. Chapter 4 In: Bacpoles Final Report - Preserving cultural heritage by preventing bacterial decay of wood in foundation piles and archaeological sites, Editor Dr. René Klaassen. Wageningen, The Netherlands 51 pp. Wood Moisture Content The fiber saturation ti point is when the wood cell wall is saturated with bound water. The moisture content at FSP is 20 to 30% < FSP Bound water > FSP Free water 20

21 12% Equilibrium moisture content 21

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23 > FSP Decay will only occur above the fiber saturation point or above 20% moisture 23

24 Effect of Wood Moisture Content on Wood Strength Properties FSP A B C D E Tension parallel to the grain Bending Compression parallel to the grain compression perpendicular to the grain tension perpendicular to the grain Source: The Wood Handbook USDA Forest Products Laboratory Effect of Decay on Wood Strength Properties At 5% to 10% weight loss, strength properties can be reduced from 20 to 80% Type of decay fungus yp y g Wood species Strength property measured 24

25 Relative Humidity / Moisture Requirements for Fungal Growth on Surfaces Water activity (a w ) = relative humidity / 100 hydrophilic fungi a w > 0.90 mesophilic fungi a w 0.80, 0.90, optimum >0.90 xerotolerant minimum a w <0.80 optimum >0.80 maximum 1.00 xerophilic fungi minimum a w <0.80 maximum <0.97 Lower limits of relative humidity to support the growth of fungi Clarke, J.A., Johnstone, C.M., Kelly, N.J., McLean, R.C., Anderson, J.A. Rowan, N.J. and J.E. Smith A technique for the prediction of the conditions leading to mould growth in buildings, Building and Environment Vol 34, pages

26 Types of Fungi Molds: Ascomycetes and Deuteromycetes Wood Sapstain fungi: Ascomycetes and Deuteromycetes Wood Decay fungi: Brown rot: Basidiomycetes White rot Basidiomycetes Soft rotascomycetes and Deuteromycetes Mold Surface only: Decay Within the wood: 26

27 Moisture Requirements for Wood Decay Most wood-decay fungi are hydrophilic and require a water activity of at least 0.97 Decay fungi will start to grow on wood with a moisture content of 27% This corresponds to a relative humidity of > 97%, unless a source of free water is present Moisture Requirements for Mold growth Many mold fungi can tolerate lower relative humidity than wood-decay fungi, although optimal growth occurs at high relative humidity Lower limit of tolerance for growth to occur has been reported as 75 to 80% relative humidity 27

28 Mold growth on surfaces will occur at >80% relative humidity Moisture Requirements for Mold growth Many mold fungi can tolerate lower relative humidity than wood-decay fungi, although optimal growth occurs at high relative humidity WHY? There is evidence that spores of xerophilic fungi have greater moisture holding capacity 28

29 Moisture Requirements for Stain fungi Studies have shown that sapstain development can occur at or very near the fiber saturation point. The minimum relative humidity tolerated by the sapstain fungus, Ophiostoma piceae was 93-94% RH corresponding to a wood moisture content of 21 to 22% at 15ºC. Temperature requirements for fungi Temperature influences enzymatic activities. Enzymes are inactivated at elevated temperatures. A temperature as low as 30ºC can inactivate enzymes. Mesophiles-Most fungi are mesophiles; existing at temperatures between 10 and 40ºC Psychrophiles can survive cold temperatures in arctic climates and at high elevations. Optimal temperatures for psychrophiles is 8-10ºC C, with a range from 4 to 12ºC C. Thermophiles exist at optimal temperatures of 20º to >50º C. These have been recovered from areas around volcanoes, after forest fires, compost piles, and dry kilns. Many competing fungi are eliminated, allowing them to flourish. 29

30 Temperature requirements for fungi Most thermotolerant fungi are molds (but few molds are thermotolerant) Most wood-decay fungi are mesophiles and exist at temperatures t from 10 to 40 ºC Wood sterilization Wood utility pole sterilization temperature is 65 ºC (150 ºF). To sterilize wood for laboratory studies it is placed in an autoclave a at 121ºC at 15 psi for 15 minutes 30

31 Pole sterilization Current AWPA standard M for drying southern pine poles requires that kiln-drying temperatures reach 150 F (65.5 C) at the pith for 1 hour (AWPA 2001). The AWPA UCS Standard T1, however, specifies air-drying or kiln-drying as acceptable conditioning methods for southern pine poles. ANSI standard , section , for sterilization of poles, also requires drying temperatures to reach 150 F at the pith for 1 hour (ANSI 2002). Results of microbial isolations in 20 utility poles in 4 stages of treatment (Cooper et al. 1998). Microbes isolated Frequency of Isolations in Sapwood and Heartwood Before Treatment Ater treatment After Fixation After Kiln drying SW HW SW HW SW HW SW HW Hyphomycetes: Alternaria alternata Aureobasidium sp Aureobasidium pullulans Curvularia inaequalis Hormonema dematioides Paecilomyces variotti Penicillium sp Penicillium diversum Sporothrix sp. B Trichoderma sp Basidiomycetes White rot (1) White rot (2) Cooper, P. et al Temperature development and sterilization of red pine during CCA treatment, elevated temperature fixation and drying. Material und Organismen 32(2):

32 Survival temperatures of thermotolerant fungi as determined from various sources. Fungus MaxTemp. Max. time Source Aspergillus fumigatus 65ºC 72 hours Hulme and Stranks, º 168 hours Payne et al., º Wakeling and van der Waals, 1996 Aureobasidium pullulans 60ºC 24 hours Hulme and Stranks, 1976 Paecilomyces variotii 50ºC 168 hours Payne et al., º 24 hours Cooper et al., º 8 hours Cooper et al., ºC Cooney and Emerson(1964) 50ºC Samson&; Hoekstra s (1988) Molds Molds have pigmented spores and colorless hyphae Colors can be black, gray, green, orange, red or purple. They occur on surfaces of freshly sawn timber or wood in service that is exposed to moisture. Usually mold growth is only on the surface and can be removed. Some molds may have the ability to detoxify preservatives, and in this manner can provide conditions that are conducive for decay fungi to colonize and attack the wood. 32

33 Stachybotrys chartarum Penicillium sp. 33

34 Trichoderma sp. common in indoor air, in soil, on wood and plant material, a common mold on stored lumber, also causes soft rot of wood mycotoxins: chrysophanol, trichodermin, trichotoxin A, many others Sources: Wang, C.J.K. and R.A. Zabel Fungi in Utility Poles. Samson,Robert A Ecology, detection and identification problems of moulds in indoor environments. In Bioaerosols, Fungi and Mycotoxins: Health Effects, Assessment, Prevention and Controls, Ed. E. Johanning. Sapstain Sapstains have pigmented hyphae h and grow primarily in the parenchyma cells of sapwood. The pigments are melanin-based and are dark brown in the hyphae, but color the wood blue. Sapstain is sometimes referred to as bluestain. Some sapstains release pigments into the wood. 34

35 Aureobasidium pullulans Growth of Aureobasidium pullulans into the parenchyma cells of wood. 35

36 Growth rate of blue stain across a board Penetration can be rapid and growth over a 24-hour period has been measured as 0.5 mm tangentially, 1 mm radially, and 5.0 mm longitudinally. Forms wedge-shaped stains on cross section. Stain can seem to suddenly appear, when in fact the hyphae may have invaded the wood 5 to 6 days prior to discoloration. The hyphae do not begin producing pigment until they are mature. Young hyphae are colorless, older hyphae produce melanin-based pigments. 36

37 Sapstains fall into two broad groups: 1. Sapstains that occur during log storage or lumber seasoning. These are sometimes associated with insect attack. Insects tunnel into the bark or wood and carry spores. These include the fungi: Ceratocystis coerulescens, Ceratocystis pilifera, Ophiostoma spp. 2. Sapstains that occur on wood products in a wide range of uses, when airborne spores land on wood and moisture/temperature conditions are conducive to their growth. Such opportunistic fungi include Aureobasidium pullulans, Cladosporium herbarum, Alternaria alternata, Stemphylium, Phialophora spp. Conditions that favor growth of sapstain fungi Sapstain fungi require free water, temperature of 4 to 30ºC oxygen, food source 2 conditions favor sapstain development in logs/lumber: wood that is seasoned under high MC conditions, not dried rapidly enough lumber with a large % of sapwood 37

38 Sapstain development Moisture content is the critical factor in stain development Sapstain develops under warm, humid conditions in wood with a large percentage of sapwood. Spores or mycelial fragments land on the surface, moisture allows growth. Or insects act as vectors, carrying sticky spores onto the wood surface. Spores germinate or hyphae grow into torn cell walls and exposed ray cells. They grow into ray and longitudinal parenchyma cells, pass through pits, enter longitudinal cells also (tracheids, fibers, vessels) via pits from ray cells. Sources of infection on unseasoned timber Spores or mycelial fragments Airborne spores, wind, some of the fungi that cause stain are ubiquitous; their spores are always present in air. Soil contact-during storage Rain, water splash from soil or other contaminated wood Contaminated wood dust can contaminate fresh wood. Contact with other infected wood such as stickers when sawn boards are stacked for air-seasoning Insect vectors Bark beetles can carry spores and infect a standing tree or wood after cutting. Ambrosia beetles form pinholes in wood and carry fungi that cause a stain around the pinhole Mites and other beetles can carry spores to wood, especially wood that is close to soil. 38

39 Effects of sapstain on Wood Properties Changes in appearance changes changes in color reduces value and limits its use in certain applications Effect on strength-- no strength loss Erosion of pit membranes and parenchyma cells causes increased permeability to water, finishes and preservatives Control of sapstain Rapid drying, kiln-drying or air seasoning with good ventilation. Stack boards with a roof on top, enough room between stacks. Dip or spray with fungicide. These treatments are to prevent growth prior to drying and are not meant as wood preservatives during use 39

40 Control of sapstain Ponding or spraying with water. This keeps MC high enough to prevent fungal growth by limiting oxygen supply. Utilize wood rapidly Protect from rain Use preservative-treated stickers Stack wood properly Biocontrol Block pigment formation in fungi chemical treatment or bioengineering Pole Sterilization Study Objectives To examine fungal populations in poles during processing To determine the effects of kiln drying and CCA treatment on fungal viability To determine the extent of potential re-colonization after storage between kiln drying and CCA treatment Anagnost et al Fungi inhabiting southern pine utility poles during manufacture. Forest Products Journal 56(1):

41 SITE A: Processing steps when cores were removed for sampling: For 10 poles: 1. One day prior to kiln drying hours after kiln drying 3. One day after CCA treatment (8 of 10 poles) For two of the initial iti 10 poles: 2B. 12 weeks after kiln drying 3B. One day after CCA treatment after 12 weeks storage 41

42 At each site two untreated poles were left exposed after kiln drying Site A: 12 weeks of storage after drying Site B: 2, 4, 6, and 8 weeks of storage after drying SITE A 42

43 SITE A 12 weeks after kiln drying SITE A 43

44 SITE A Numbe er of fungi isolate ed per core from each pol le SITE A pre-processing after kiln POLE drying # after CCA treatment 44

45 Numb ber of fungi isolate d per core le from ea ch pol SITE A POLE # pre-processing after kiln drying after CCA treatment after kiln drying and 12 w eeks storage After 12 w eeks storage and Cca treatment SITE A Number of Fungal Colonies Recovered at Each Processing Step 1--Pre processing 2A--After kiln drying 3A--After CCA treatment 2B--after KD and storage for 12 weeks 3B--CCA treatment after storage for 12 weeks total # of isolates 20coes cores 20cores 16cores 8cores 8cores 72 cores Mitosporic fungi (Microfungi) Zygomycetes Basidiomycetes Yeasts Sterile isolates total isolates examined isolates to be examined total isolates

46 SITE A Mitosporic fungi (Microfungi) including soft rot fungi, molds and stainers Species or Genus or group 1--Pre processing 2A--After kiln drying 3A--After CCA treatment 2B--after KD and storage for 12 weeks 3B--CCA treatment after storage for 12 weeks total # of isolates Hyphomycetes Alternaria sp Aureobasidium sp Fusarium sp Gliocladium sp Hormoconis resinae Paecilomyces variotii Sporotrichum sp Sporotrichum sp Trichoderma harzianum Trichoderma konigii Trichoderma sp Coelomycetes Diplodia sp Pestalotiopsis sp SITE B pole 1 pole # of isolates Week of storage 46

47 Pole Study Conclusions Current commercial kiln drying and CCA treatment procedures are very effective for sterilizing southern pine utility poles For maximization of long-term performance storage time between kiln drying and CCA treatment should be limited to two weeks to prevent significant recolonization of fungi Variations in climate and weather have a dramatic effect on the extent of colonization by fungi Storage before and after kiln drying Importance of protection from rain or other moisture sources before kiln drying Importance of storing green logs or lumber to allow sufficient air flow to minimize mold growth S l /l b f f Store green logs/lumber away for sources of contamination Importance of protection from rain or other moisture sources after kiln drying 47

48 Questions? 48