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
1.
Wood +Water = Decay
1
The process of wood decay requires:
2. Fungus
1. Substrate
3. Moisture
Temperature
• Cellulose
• Hemicellulose
• Lignin
Li i
2
Three Types of Wood Decay
•Brown
Brown rot
•White rot
•Soft rot
•(bacteria)
Wood Decay Fungi
Brown-rot fungi
Basidiomycetes
White-rot fungi
Basidiomycetes
Soft-rot fungi
“Microfungi”:
Hyphomycetes
Coelomycetes
Ascomycetes
3
BROWN ROT
Consumes cellulose
and hemicelluloses
Does not attack
lignin
Results in rapid
strength loss
4
Brown Rot
Cubical rot
Cubical pocket rot
Dry rot
“Building rot fungus”
Cubical “pocket” rot
Incense cedar
Postia amara
5
Brown Rot of Oak – Lenzites trabea
Rhizomorphs by the dry rot fungus Meruliporia incrassata
6
Mycelial fan by the dry rot fungus Meruliporia incrassata
7
Bore holes in Douglas-fir
by Poria carbonica
Brown rot fungus in
Southern pine
Hyphae with clamp
connections (arrows)
8
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
Simultaneous rot
“zone lines”
White rot in a Douglas-fir utility pole after 10 years of service
10
11
Simultaneous White Rot
Cell wall thinning
Simultaneous White Rot
Trametes versicolor on the lumen
surface of a Southern Pine
tracheid
12
Simultaneous White Rot
Bore holes
Selective delignification
cell separation –
degradation of the middle
lamellae
“Biopulping”
Yellow birch
by the fungus Mycena leaiana
13
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
15
Soft rot cavities in southern pine in cross section
Soft rot Type 1
Cavities in the
S2 cell wall layer
16
Soft rot Type 1
Cavities in the
S2 cell wall layer
17
Soft rot cavity formation
Soft rot cavity formation
Longitudinal view of chains
of diamond- shaped cavities
18
Soft rot Type 1
Diamond cavities in a southern pine tracheid
BACTERIA
Degradation of s
submerged
bmerged wood
ood
Conditions of low oxygen
19
Erosion 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
The fib
Th
fiber saturation
t ti point
i t is
i when
h th
the wood
d
cell wall is saturated with bound water.
The moisture content at FSP is 20 to 30%
< FSP
> FSP
Bound water
Free water
20
12% Equilibrium moisture content
21
22
> FSP
Decay will only occur above the fiber
saturation point or above 20% moisture
23
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. 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
yp of decay
y fungus
g
–Wood species
–Strength property measured
24
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
optimum
ti
>0.80
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.
25
Types of Fungi
• Molds:
Ascomycetes and Deuteromycetes
• Wood Sapstain fungi: Ascomycetes and
Deuteromycetes
• Wood Decay
y fungi:
g
– Brown rot: Basidiomycetes
– White rot
Basidiomycetes
– Soft rotAscomycetes and Deuteromycetes
• Mold
– Surface only:
• Decay
– Within the wood:
26
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
• M
Many mold
ld ffungii can tolerate
l
llower
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
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
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
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
8-10 C, with a range from 4 to 12ºC
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.
29
Temperature requirements for fungi
• Most thermotolerant fungi are molds (but few
molds are thermotolerant)
• Most wood-decay fungi are mesophiles and
exist
i t att temperatures
t
t
from
f
10 to
t 40 ºC
Wood sterilization
• Wood utility pole sterilization
temperature is 65 ºC (150 ºF).
• To sterilize wood for laboratory studies
it iss p
placed
aced in a
an au
autoclave
oc a e a
at 121ºC
Ca
at
15 psi for 15 minutes
30
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
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.
2
4
3
4
2
6
1
4
1
501
0
2
0
1
0
4
22
3
0
123
0
1
1
1
0
3
1
5
0
137
2
1
5
0
0
7
1
21
0
65
0
0
0
0
0
2
0
0
0
0
2
1
0
2
0
1
0
0
0
0
0
0
0
0
0
35
9
5
0
0
0
0
0
0
0
44
10
5
0
0
55
0
32
0
4
0
18
5
0
0
1
0
0
0
0
0
Basidiomycetes
White rot (1)
White rot (2)
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.
31
Survival temperatures of thermotolerant fungi as
determined from various sources.
Fungus
MaxTemp.
Max. time
Source
Aspergillus fumigatus
65ºC
50º
50º
72 hours
168 hours
Hulme and Stranks, 1976
“
“
Payne et al., 1998
Wakeling and van der Waals, 1996
Aureobasidium pullulans 60ºC
24 hours
Hulme and Stranks, 1976
Paecilomyces variotii
168 hours
24 hours
h
8 hours
Payne et al., 1998
“
“
“
50ºC
50º
65º
47ºC
50ºC
Cooper et al., 1998
Cooper et al., 1998
Cooney and Emerson(1964)
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.
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
Stachybotrys chartarum
Penicillium sp.
33
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:
t i
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, Prevention
and Controls, Ed. E. Johanning.
Sapstain
• S
Sapstains
t i have
h
pigmented
i
t dh
hyphae
h and
d 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
Aureobasidium
pullulans
Growth of Aureobasidium pullulans into the parenchyma cells of wood.
35
Growth rate of blue stain across a
board
• Penetration can be rapid
p and g
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
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 off uses, when
h airborne
ib
spores lland
d on wood
d
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
water,
temperature of 4 to 30ºC
• oxygen, food source
p
development
p
• 2 conditions favor sapstain
in logs/lumber:
– wood that is seasoned under high MC
conditions, not dried rapidly enough
– lumber with a large % of sapwood
37
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
air.
•
Soil contact-during storage
•
•
•
Rain, water splash from soil or other contaminated wood
•
Contact with other infected wood such as stickers when sawn boards are stacked for
air-seasoning
•
Insect vectors
Contaminated wood dust can contaminate fresh wood.
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
Effects of sapstain on Wood
Properties
• Changes in appearance—changes
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 increased
permeability to water, finishes and
preservatives
Control of sapstain
•
•
Rapid drying,
drying kiln
kiln-drying
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
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. 2006. Fungi inhabiting southern pine utility poles during manufacture. Forest
Products Journal 56(1): 53-59.
40
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)
For two
F
t
off the
th initial
i iti l 10 poles:
l
2B. 12 weeks after kiln drying
3B.
One day after CCA treatment after 12 weeks storage
41
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
SITE A
12 weeks after kiln drying
SITE A
43
SITE A
Numbe
er of fungi isolate
ed per core
from each polle
SITE A
14
12
10
8
6
4
2
0
1
2
3
pre-processing
4
5
af ter kiln
drying
POLE
#
9
10
11
12
13
af ter CCA treatment
44
SITE A
Num b
be r of fungi isola te
e d pe r core
from e a ch polle
25
20
15
10
5
0
1
2
3
4
5
PO LE #
9
10
11
12
13
pre-proc es s ing
af ter kiln dry ing
af ter CCA treatment
af ter kiln dry ing and 12 w eeks s torage
A f ter 12 w eeks s torage and Cc a treatment
SITE A
Number of Fungal Colonies Recovered at Each Processing Step
1--Pre
processing
2B--after KD
2A--After kiln 3A--After CCA and storage
drying
treatment
for 12 weeks
3B--CCA treatment
after storage for 12
weeks
total # of
isolates
20
0 co
cores
es
20
0 co
cores
es
16
6 co
cores
es
8 co
cores
es
8 co
cores
es
72 co
cores
es
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
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
77
97
292
Mitosporic fungi (Microfungi)
Sterile isolates
total isolates
45
SITE A
Mitosporic fungi (Microfungi) including soft rot fungi, molds and stainers
Species or Genus or group
1--Pre
2A--After kiln
processing
drying
3A--After
CCA
treatment
2B--after KD
and storage
for 12 weeks
3B--CCA
treatment after
storage for 12
weeks
total # of
isolates
H h
Hyphomycetes
t
Alternaria sp.
Aureobasidium sp
Fusarium sp.
Gliocladium sp.
Hormoconis resinae
Paecilomyces variotii
Sporotrichum sp.1
Sporotrichum sp.2
Trichoderma harzianum
Trichoderma konigii
Trichoderma sp.
3
0
14
3
1
2
0
0
19
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
36
1
1
0
0
0
0
3
0
0
0
41
0
0
0
1
1
3
3
14
3
1
79
1
1
19
3
1
2
2
0
0
0
0
0
0
0
0
2
2
Coelomycetes
Diplodia sp.
Pestalotiopsis sp.
SITE B
90
81
80
75
pole 1
pole 8
70
# of isolates
60
56
50
41
40
29
30
20
10
7
3
2
0
2
4
6
8
Week of storage
46
Pole Study Conclusions
• Current commercial kiln drying and CCA treatment
procedures are very effective for sterilizing southern
pine
i utility
tilit poles
l
• 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
•Store green logs/lumber away for sources of S
l /l b
f
f
contamination
•
•Importance of protection from rain or other moisture sources after kiln drying
47
• Questions?
48