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Wood Decay, Fungi, Stain and Mold 

New England Kiln Drying AssociationSpring 2011 Meeting

April 7, 2011Oneonta, New York

Susan E. Anagnost

SUNY College of Environmental Science and ForestrySyracuse, New York

Chair and Associate ProfessorDepartment of Sustainable Construction Management and Engineering

1 The Basics of Wood Decay1. The Basics of Wood Decay

Wood +Water = Decay

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The process of wood decay requires:

1. Substrate 2. Fungus

3. MoistureTemperature

• Cellulose• Hemicellulose

Li i• Lignin

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•Brown rot

Three Types of Wood Decay

Brown rot

•White rot

•Soft rot

•(bacteria)

Wood Decay Fungi

Brown-rot fungi Basidiomycetes

White-rot fungi Basidiomycetes

Soft-rot fungi “Microfungi”:HyphomycetesCoelomycetesAscomycetes

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BROWN ROT

Consumes cellulose and hemicelluloses

Does not attack lignin

Results in rapid strength loss

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Brown Rot

Cubical rotCubical pocket rotCubical pocket rotDry rot“Building rot fungus”

Cubical “pocket” rot

Incense cedar

Postia amara

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Brown Rot of Oak – Lenzites trabea

Rhizomorphs by the dry rot fungus Meruliporia incrassata

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Mycelial fan by the dry rot fungus Meruliporia incrassata

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Bore holes in Douglas-fir by Poria carbonica

Brown rot fungus in Southern pine

Hyphae with clampHyphae with clamp connections (arrows)

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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

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Simultaneous rot

“zone lines”

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

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Simultaneous White Rot

Cell wall thinning

Simultaneous White Rot

Trametes versicolor on the lumen surface of a Southern Pine tracheid

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Simultaneous White Rot

Bore holes

Selective delignification

cell separation –degradation of the middle lamellae

“Biopulping”

Yellow birch by the fungus Mycena leaiana

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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

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Soft rot cavities in southern pine in cross section

Soft rot Type 1

Cavities in the S2 cell wall layerS2 cell wall layer

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Soft rot Type 1

Cavities in the S2 cell wall layerS2 cell wall layer

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Soft rot cavity formation

Soft rot cavity formation

Longitudinal view of chainsLongitudinal view of chains of diamond- shaped cavities

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Soft rot Type 1Diamond cavities in a southern pine tracheid

BACTERIA

Degradation of s bmerged oodDegradation of submerged wood

Conditions of low oxygen

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Erosion bacteria in wooden building support pilesErosion bacteria in wooden building support piles

From:Nilsson, T. and C. Björdal. 2005. 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

Th fib t ti i t i h th dThe fiber saturation 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

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12% Equilibrium moisture content

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> FSP

Decay will only occur above the fiber

saturation point or above 20% moisture

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Effect of Wood Moisture Content on Wood Strength Properties

FSP

A Tension parallel to the grainB BendingC Compression parallel to the grainD compression perpendicular to the grainE tension perpendicular to the grain

Source: The Wood Handbook. 1999. 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 fungusyp y g–Wood species–Strength property measured

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Relative Humidity / Moisture Requirements for Fungal Growth on Surfaces

Water activity (aw) = relative humidity / 100

• hydrophilic fungi aw > 0.90

• mesophilic fungi aw ≥ 0.80,≤ 0.90, optimum >0.90

• xerotolerant minimum aw <0.80 ti 0 80optimum >0.80

maximum 1.00

• xerophilic fungi minimum aw <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. 1999. A technique for the prediction of the conditions leading to mould growth in buildings, Building and Environment Vol 34, pages 515-521.

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Types of Fungi• Molds: Ascomycetes and Deuteromycetes

• Wood Sapstain fungi: Ascomycetes and Deuteromycetes

• Wood Decay fungi:y g

– Brown rot: Basidiomycetes

– White rot Basidiomycetes

– Soft rotAscomycetes and Deuteromycetes

• Mold– Surface only:

• Decay– Within the wood:

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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

M ld f i l l

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

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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?WHY?– There is evidence that spores of xerophilic

fungi have greater moisture holding capacity

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• Studies have shown that sapstain

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.A temperature as low as 30 C 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 with a range from 4 to 12ºCpsychrophiles is 8-10 C, with a range from 4 to 12 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.

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Temperature requirements for fungi

• Most thermotolerant fungi are molds (but few molds are thermotolerant)

• Most wood-decay fungi are mesophiles and i t t t t f 10 t 40 ºCexist at temperatures from 10 to 40 ºC

Wood sterilization

• Wood utility pole sterilization• Wood utility pole sterilization temperature is 65 ºC (150 ºF).

• To sterilize wood for laboratory studies it is placed in an autoclave at 121ºC at s p aced a au oc a e a C a15 psi for 15 minutes

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Pole sterilization

• Current AWPA standard M1-01 1.1.5 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 05.1-2002, section 5.1.2.6, 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

SW HW SW HW SW HW SW HW

Hyphomycetes:

Frequency of Isolations in Sapwood and HeartwoodBefore Treatment Ater treatment After Fixation After Kiln drying

Alternaria alternata 2 0 0 2 0 2 0 0Aureobasidium sp. 4 2 1 1 0 1 0 0Aureobasidium pullulans 3 0 1 5 0 0 0 0Curvularia inaequalis 4 1 1 0 0 2 0 0Hormonema dematioides 2 0 0 0 0 0 0 0Paecilomyces variotti 6 4 3 7 2 1 35 44Penicillium sp. 1 22 1 1 0 0 9 10Penicillium diversum 4 3 5 21 0 0 5 5Sporothrix sp. B 1 0 0 0 0 0 0 0Trichoderma sp. 501 123 137 65 0 0 0 0

Basidiomycetes

White rot (1) 55 32 4 18 0 1 0 0White rot (2) 0 0 0 5 0 0 0 0

Cooper, P. et al. 1998. Temperature development and sterilization of red pine during CCA treatment, elevated temperature fixation and drying. Material und Organismen 32(2):127-143.

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Survival temperatures of thermotolerant fungi as determined from various sources.

Fungus MaxTemp. Max. time Source

Aspergillus fumigatus 65ºC 72 hours Hulme and Stranks, 1976

“ 50º 168 hours Payne et al., 1998

“ 50º Wakeling and van der Waals, 1996

Aureobasidium pullulans 60ºC 24 hours Hulme and Stranks, 1976

Paecilomyces variotii 50ºC 168 hours Payne et al., 1998

h“ 50º 24 hours Cooper et al., 1998

“ 65º 8 hours Cooper et al., 1998

“ 47ºC 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 removedremoved.

• 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.

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Stachybotrys chartarum

Penicillium sp.

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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

t i•mycotoxins: chrysophanol, trichodermin, trichotoxin A, many others

Sources:Wang, C.J.K. and R.A. Zabel. 1991. Fungi in Utility Poles.Samson,Robert A. 2001. Ecology, detection and identification problems of moulds in indoor environments. In Bioaerosols, Fungi and Mycotoxins: Health Effects, Assessment, Preventionand Controls, Ed. E. Johanning.

Sapstain

S t i h i t d h h d• Sapstains have pigmented hyphae 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.

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Aureobasidiumpullulans

Growth of Aureobasidium pullulans into the parenchyma cells of wood.

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Growth rate of blue stain across a board

• Penetration can be rapid and growth over a 24-hour p gperiod 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 priorhyphae 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.

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Sapstains fall into two broad groups:

• 1. Sapstains that occur during log storage or lumber1. 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 f h i b l d drange 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• Sapstain fungi require free water, temperature of 4 to 30ºC

• oxygen, food source

• 2 conditions favor sapstain development p pin logs/lumber:– wood that is seasoned under high MC

conditions, not dried rapidly enough– lumber with a large % of sapwood

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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 airare 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 vectorsBark 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 pinholeMites and other beetles can carry spores to wood, especially wood that is close to soil.

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Effects of sapstain on Wood Properties

• Changes in appearance—changes inChanges in appearance 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 increasedparenchyma cells causes increased permeability to water, finishes and preservatives

Control of sapstain

• Rapid drying kiln drying or air• 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

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Control of sapstain

• Ponding or spraying with water. This keepsPonding 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• Stack wood properly• Biocontrol• Block pigment formation in fungi—chemical

treatment or bioengineering

Objectives

Pole Sterilization Study

•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. 2006. Fungi inhabiting southern pine utility poles during manufacture. Forest Products Journal 56(1): 53-59.

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SITE A:

Processing steps when cores were removed for sampling:

For 10 poles:1. One day prior to kiln drying

2. 30 hours after kiln drying

3. One day after CCA treatment (8 of 10 poles)

F t f th i iti l 10 lFor two of the initial 10 poles:2B. 12 weeks after kiln drying

3B. One day after CCA treatment after 12 weeks storage

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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

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SITE A

12 weeks after kiln drying

SITE A

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SITE A

10

12

14

ed

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le

SITE A

4

6

8

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sola

te

fro

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ach

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0

2

1 2 3 4 5 9 10 11 12 13

POLE #

Nu

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e

pre-processing af ter kiln drying af ter CCA treatment

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20

25

ed

pe

r c

ore

le

SITE A

5

10

15

be

r o

f fu

ng

i is

ola

te

fro

m e

ac

h p

ol

01 2 3 4 5 9 10 11 12 13POLE #

Nu

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pre-process ingaf ter kiln dry ingaf ter CCA treatmentaf ter kiln dry ing and 12 w eeks s torageA f ter 12 w eeks s torage and Cca treatment

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

weekstotal # of isolates

20 cores 20 cores 16 cores 8 cores 8 cores 72 cores

Number of Fungal Colonies Recovered at Each Processing Step

SITE A

0 co es 0 co es 6 co es 8 co es 8 co es co es

Mitosporic fungi (Microfungi) 48 0 0 38 46 132

Zygomycetes 0 0 0 0 1 1

Basidiomycetes 2 0 0 0 1 3

Yeasts 0 1 0 0 0 1

Sterile isolates 67 0 0 0 0 67

total isolates examined 117 1 0 38 48 204

isolates to be examined 0 0 0 39 49 88

total isolates 77 97 292

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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

Mitosporic fungi (Microfungi) including soft rot fungi, molds and stainers

Species or Genus or group

H h t

SITE A

Alternaria sp. 3 0 0 0 0 3

Aureobasidium sp 0 0 0 0 3 3

Fusarium sp. 14 0 0 0 0 14

Gliocladium sp. 3 0 0 0 0 3

Hormoconis resinae 1 0 0 0 0 1

Paecilomyces variotii 2 0 0 36 41 79

Sporotrichum sp.1 0 0 0 1 0 1

Sporotrichum sp.2 0 0 0 1 0 1

Trichoderma harzianum 19 0 0 0 0 19

Hyphomycetes

Trichoderma harzianum 19 0 0 0 0 19

Trichoderma konigii 2 0 0 0 1 3

Trichoderma sp. 0 0 0 0 1 1

Diplodia sp. 2 0 0 0 0 2

Pestalotiopsis sp. 2 0 0 0 0 2

Coelomycetes

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75

70

80

90

pole 1

pole 8

SITE B

56

29

41

20

30

40

50

60

# of

isol

ates

37

2

0

10

20

2 4 6 8

Week of storage

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Pole Study Conclusions

• Current commercial kiln drying and CCA treatment procedures are very effective for sterilizing southern

i tilit lpine 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 fungirecolonization 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

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• Questions?