-u--.-s-=.--. -
AGRICULTURE ROOM
U. S. Department of Agriculture, LForest Servic e
FOREST PRODUCTS LABORATOR Y
In cooperation with the University of Wisconsi n
MADISON, WISCONSIN
TEMPERATURES NECESSARY TO KIL L
FUNGI IN WOO D
By MAE SPRADLING CHIDESTE R
Junior
Pathologis t
SCI-IM
.)Rr; T
Published in
Proceedings of the
AMERICAN WOOD PRESERVERS' ASSOCIATIO N
1937
TEMPERATURES NECESSARY TO KILL FUNGI IN WOOD By
MAE SPRADLING CHIDESTER2
Junior Pathologist, Division of Forest Pathology3 .
Bureau of Plant Industry, U, S . Department of Agricultur e
L
INTRODUCTION
Because incipient decay in wood is frequently difficult t o
detect, poles, piling, cross ties, and heavy structural timbers which con 1
tain decay organisms are often considered sound . Operators of wood-preI
serving plants as well as the people who use treated materials frequentl y
inquire whether the temperatures employed during treating processes ar e
t
sufficienconnection
any fungi that might be i the wood . Sim lar question s
., and Snell
aris eic
_ i enco n o kill with kiln drying . Hoxi a-, Hubert ., Long
1
reported the temperatures to which wood was subjected in order to kil l
• • , fungi in it, but their data are of limited applicatio4, AingA n 9i record wa s
- made of the internal temperatures obtained . MacLean-' -' -, - recentl y
showed that the internal temperature attained by wood under heat treatmen t
;,`, .
•
-Presented before the 33rd annual meeting of the American Wood-Preserver s ,
Association, New Orleans, La ., January 26-28, 1937 .
?The author wishes to express her appreciation to C . A . Richards and J . D .
MacLean for their helpful suggestions and criticisms during the investi gation reported in this paper, and to M . E . Dunlap and R . C . Rietz fo r
their assistance in the construction of some of the apparatus used i n
the experiments .
■. ' ;
3Maintained at Madison, Wis ., in cooperation with the Forest Product s
Laboratory .
-Hoxie, F . J . Dry rot in factory timbers, Inspection Dept ., Associate d
Factory Mutual Fire Insurance Companies, Boston, pp . 23-38 . 1930 .
--
'
Hubert, E . E . The heat treatment of infected wood, Hardwood Record 57
15, 18, 20, Oct . 10, 192+ ; 58(1) : 18, 20, Oct . 25, 1924 .
I
(12) :
Long, W . H . When is rot not rot? Amer . Wood-Preservers' Assn . Proc .
1925, pp . 202-219 ; and 1 927, pp . 70-77 .
'Snell, W . H . The effect of heat upon the mycelium of certain structura l
timber-destroying fungi within wood . Amer . Jour . Bet . 10 ;399-411 .
Oct . 1923 .
(Footnotes 8, 9, 10, 11 on page 2 . )
R11 4#8
depends upon the species of wood used, the 4AMdh6ibns and moisture contend :
of the materials, as well as the tempexatwe and time to w1 .h the wooctr 40
exposed .The purpose of the i ivestigat! s re-potted here Ae* to determin e
the internal temperatures and, their durations necessary to kUl ceri i
fungi in wood .
I TH071S .
apwood sticks cut from green loblol:1 pl4e (I.? ri ,taeda inn,.. )
1 by 1 by 10 inches, were placed in 500 by 50 mm test tibes c.ontai!ng 5 0
cc of distilled water . Each stick was supported on glass so that its lowe
r
end came within 1/2 inch of the surface of the water . The tubes were tha n
plugged with cotton and sterilized by steaming for 30 minutes. at 212° F.
After the wood cooled it was inoculated with either Poria incras•$nta (B ,
& C .) Burt ., Lenzites sepiata'a 7r ., or Lentinusle Ad:eus Fr . The Zirst
named is the most common buil,cling rot fungus in the South ., arid the other s
are common decay fungi in pine prodaets . These sticks nitre incubated a t
room temperature (72 0 to 90° F .) until they were thorouglvl.y infected viii}
the fungus . This usually required a period of 4 to 6 weeks... In order t o
determine whether the sticks were thoroughly infected, 1 out of each 1 0
(selected at random) was split and 12 bits of wood (about 1/i-inch e- bes )
were cut from the interior and planted on malt agar . Any fungi liv*ng i n
the sticks grew out on the agar .
n khP st$Oko. were thpr. ourghly inf eeted, they wore removed fro m
fung i
growth was removed: by scraping . he i'
•i.cks for moisture determinations . These.
tely and dried in a drying oven (21 20
The mo sturv content was determine d
•,-, .
were
.,kept
the interns
, between .
plat e
wood an d
14,01,0511 0. O. Studies of heat oonductidn TIT44010 Ite alts of steamin g
*raft 2ound ;southern pine timbers . American
reservers' As p, .
rt- kW,
.
. 1_97-219
'its of heat conduction in
steaming grrsived southern pine timbers .
►
u pp. 303-330 .
Te
Amer . Viood-PreseVORK ,
,tIppnixturi change
&. oc . 1935, pp .
st Douglas Maw
,
the temperatures applied at the surfaces of these sticks . MacLean' s
method of measuring internal temperatures was followed . A thermocoupl e
was inserted in a 116-inch hole that extended approximately to the cente r
of the stick (Fig . 1) . A white pine peg was used to plug the hole an d
hold the thermocouple in place during heating . Care was taken not t o
bind the thermocouple with the peg .
1
The methods of heating the sticks were as follows : In an auto clave at 212° F . ; between two heated plates at 212°, 194°,185°, 167°, and
149° F . ; and in an electric drying oven at 194°, 185°, 167°, and 149° F.
with relative humidities ranging from 35 to 4+0 percent and 90 to 97 percent .
Preliminary tests were run with each heat treatment to narro w
the range of temperature and heating periods that would kill the fungi .
More extensive tests were then run using these critical ranges .
Sticks to be heated with steam (212° F .) were placed on a wir e
rack in a preheated autoclave (26 by 36 inches) . Two records of th e
temperature within the autoclave were taken : one with a thermocouple leading from near the stick (about 1 inch away) through a rubber stopper i n
an opening at the top of the autoclave to a potentiometer indicator ; and
one taken with a thermometer built into the autoclave so that it measure d
the temperature 3 inches from the top . The internal temperature of th e
stick was measured with a thermocouple placed inside the stick, a s
already explained (Fig . 1) .
Sticks heated by the plate method were placed between hollow cas t
iron baffle plates (3 by 18 by 18 inches), which were heated by hot circu lating motor oil (Fig . 2) . The oil, heated in a tank by an electri c
heater, was circulated through the plates as indicated in the diagram .
The temperature of the oil, and, consequently, the temperature of th e
plates, was held constant while the specimens were heated . The temperature of the plates was measured on the top and bottom by thermocouples .
A specimen heated between the plates was flanked on the sides with tw o
pieces of wood the same size as the specimen to prevent evaporation o f
moisture .
The use of heated plates for temperature studies on wood wa s
initiated by MacLean of the Forest Products Laboratory . The hot plat e
method was adopted in order to heat wood specimens below the temperatur e
of steam (212° F .) and yet employ a method of heating similar to steam i n
its effect on green wood .
The apparatus used to heat the wood specimens in moist air was
a constant temperature drying oven with an automatic humidifier . In brief ,
the humidifying system consisted of a wood-element hygrostat? set on th e
•
12
-Loughborough, W . K ., and Rietz, R . C . A sensitive wood element hygrostat .
Instruments 5(6) :143-144, A15, June 1932 .
R11tFS
-3-
oiled ci r
an electric .
de of the oven, whi
The relative humidi y was determined y
ted a water evapor
the wet and dry bulb method . An, electric fan
'dew point metho d1
t !erder to maintain a uniform temperatur e
was used t 'rculate the
Ogariilin the oven'1'he internal temperature of the stick s
xe record as described fot th e
-Q;f the over
„
JI sma .
were sp
a e of the sec t
iNerile malt agar .
It least 3 week s
fungous gre w
had ber ki
-
_
th
a
differen t
of time are- '
es app l
the average .
ting, for
e
is an
for stick s
the internal
riod for an external tempera e period . Lentinus lepideus
to h t than . . incrassata .
the
of differen
The resul t
used to -
temper :
in an e
_
-
7
ire d
eriod to kil
th
' ere of
relativ e
humT. t than w
n o
ince the atmos phere within th e tti ck s
st saturated, on e
would expect the length
emp eratur e
the case of sticks heated between plates woo l
ant from
that required in air at 90 to 97 percent relativ e
s is
verified by results shown in Figure 3. In two out
temperatures in these two treatments the duration re q
same . In one case, 149° F ., the duration required t o
-longer in the moist air, 90 to 97 percent relative humidity
,
1
Marvin C . F . Vapor pressure, relative humidity, and temperature of th e
dew point . U . S . Dept . Agr . Weather Bureau, No . 235, p . 11 . 1915 .
R114S
_4_
tndicatfkilled if the 4'emperalkpg in the:
d
F ., 30 minutes at 170 071%, 20 minutes a
minutes at 0° F., o r
5 minutes at 212° F ., T'roviding the moist
the wood remains ~ .above fiber saturation during treatment . Vik*C condition will exist as long
via t .e medium
,phich heat is appliedat the surface of wood (fo r
4100hple, steam)
lows little water loss .
.
The results obtained from heating infected wood in air with. 3 5
to 140 percent relative humidity indicate that higher temperatures or longer
i
periods of exposure than thoso mentioned above are required to kill f
4hin wood where conditions surrounding the wood allow it to dry out dx r-
treatment .
O
inch Pinus taeda stick s
Table 1 .--Th e results obtained from heating 1 by 1 by
infected with fungi at various temperatures for different length s
of time
149°
P . Applied at Surface of Stick s
Method of heating
Moist ai r
Fungus
:Length :
: of
: time :
Hot plate
•
:heated :
Relative humidity -90 to 97 percen t
35 to 4o percen t
•
•
:Number of :Percent of :Number of :Percent of :Number of :Percent o f
sticks :sticks with : sticks :sticks with : sticks :sticks wit h
Minutes : treated :fungus dead : treated :fungus dead : treated :fungus dead
--------Poria in6
3
67
:
9
100
arassata : 20 :
3
100
25
100
: 30
10
100
100
U
100
:
60
4
100
120 :
Lentinus :
lepideus .
:
:
:
:
20
30
5
60
75
90
120
180
300
20
720
20
30
45
6o
75
90
120
180
: 300
20
720
Lenzites :
sepiaria :
:
:
:
:
:
:
2
2
3
10
10
0
50
67
4o
100
10
7
8
4o
g6
100
9
7
8
67
71
100
0
:
:
:
,
:
:
,
:
:
,
2
2
0
0
3
33
9
10
67
100
.
4
4
6
5
17
0
25
0
100
08
U
0
4
4
6
5
17
:
,
C
0
17
6o
S2
(continued on next page )
•
RliUg
167° F . Applied at Surface of Sticks
Method of heating
Moist ai r
Length :
Fungus • of
tim e
heated '
P . in:
crassata :
20
60
10
:
L':
.
lepideus :
20
30
:
:
5
6o
:
75
90
.
120
180
. 240
90 to 97 percent
100
10
3
67
10
1
1
100
10 0
10 0
10
.
:. Il '
..r
'
~,
J
12 0
.
18 0
16
100
100
100
14
.
.
10
4
6
50
50
75
17
11
10
100
100
100
4
4
4
6
11
"7 5
90
}
e rr'
u
100
4
100
100
100
100
'
""
Relative humidity -: 35 to 40 percen t
.
:Number of :Percent of :Number of :Percent of :Number of :Percent o f
sticks :sticks with : sticks :sticks with : sticks :sticks wit h
: treated :fungus dead : treated :fungus dead : treated :fungus dead
1inutes
.
Hot plat e
. 240
r
:
:
50
25
25
0
91
10
100
22
21
7
4
100
100
10 0
10 0
2
0
10
10
13
10
70
185°F . Applied at Surface of Sticks
PP .
5
incrassata : 10 T :
20
0 :
5
.
L.
: 20
lepideus : 25
30
145
. 6o
75
90
'
.91
.
Y
:
20
' "1100 '
'
r_t
'
I
~~
itt
•,1
10 - 1.
1
1
,
I
10
100
10
100
rs
i
.
10 0
100
6
90
92
100
10 0
(continued on next page )
41,
Table 1 (continued )
185 0 F . Applied at Surface of Sticks (continued )
Method of hea,tiAg
I
4
:
Fungus
Length'
▪
of
Hot plat e
time :
'heated : 90 to
Moist
--------
-
Relative humidit y
percent
: 3r5 to 40 percen t
'
:Number of :Percent of :Number of :Percent Of :Rumba• of :Percent of
sticks :'sticks with : sticks :stteka with : stifeet :sti o.ks wia.
Minutes' treated fungus dead : treated :fan:gu.s dead : treated :fungus dew'
II
7-- :
2
0
J.
20, •
10
50
:
1
.
100
sgpiaiia. : 25 :
10
100
•
20
I()
0
1
'100
10
1 15
100 :
•
13
1.@.#
60
100
IQ
75
100
6
90
▪
1940 F . Applied a t gftPit!Wee of Sticks
:
P . inVI
90
41
5
28
='assata 14 ,
1-10- n
1QO
I
97
1
.1.
,
air
---------------------------
:
..
•1
30
;
4
3
4ie
L.
1 op dens
1wO
20
3
IQ,
1
$OC
.
9
0
12
11
4
L-p
aepiaria . :
4
1020
3
IQ
60
F.
r
!
OD
teQ 1
2
10
;
0
)4e .
•
t
1p
.
1
5
1
• .able 1 (continued)
212° F . Applied at Surface of Stick s
Method of heating
Fungus
Moist ---------------air
•Length .
of .
time
'heated
Hot plate
Relative humidity -- : 35 to 40 percen t
90 to 97 percent
:Number of :Percent of :Number of :Percent of :Number of :Percent o f
: sticks :sticks .with.; sticks :sticks with : sticks :sticks with
minutes:
treated :fungus dead : treated :fungus dead : treated :fungus dead
inutes
.
.
.
? . in3 :
*20
*100
crassata :
5 :
10
100
*20
*100
. 15 :
* 3
*100
~; .
lepideus :
5
6
:
:
10
:
15
30
L.
s epiaria
5
6
10
15
30
*Heated in steam .
O
.
:
:
:
:
:
:
2
1
10
10
100
100
100
100
*6
*7
* 1
*10 0
*10 0
*100
2
1
10
10
50
100
*6
*7
* 67
* 71
50
100
*20
*3
*20
* 3
* 1
*50
*57
*10 0
*10 0
*100
0
a
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410
Table 3 .---Time-temperatures recommended to kill fungi in woo d
Heated in ai r
Heated in steam
or equivalent
.
90 to 97 percent
relative humidity
---------------------- Time
: Temperature : Time
o F . - - :- Minutes :
150
6o
35 to 40 percen t
: relative humidity
: Temperature : Tim e
° F.
: Minutes :
150
100
170
30
170
30
180
20
180
20
200
10
212
5
° F.
: Minute s
16o
:
.
190
165
6o
170
50
1 The temperature is the temperature of the wood and not the temperatur e
applied at the surface of the wood .
O
A
■
DO
a
r--"
UeA .'- 8 inch
fectea with Lenzite s
curves represen t
real
recorded
. WrisgAillgave
fir
.
Vega KN ckr4teZ I*pt curv e
IrQ' hart1ra art, Y.IW' ..Vg in moist'
.resrdgtg*, Me tim e
,Pe_eJ Sfte
b (it:Ee **A. %latlip.
oftAlairRis-4.
s,wig
' kWfir ittvagittoleiiiis,
e
O
a 1■■■
1
El■■■■
W ■a a
--
Liz
N
N
0,
N
-
W
O
en
rmrmmmmm
'
1 /3HN3d'Hd3 J'331J930
N
4
NN
p
U
O
O
6
1 /3HN36'Hbi J'331/ .730
-tea
N.
N N
1
.
p
,
]
N
~}
1 /3HA/31/Hd3 J338930
O
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