Field trials of chemicals to control
sapstain and mold on yellow-poplar
and southern yellow pine lumber
P u r c h a s e d by U. S . D e p a r t m e n t of A g r i c u l t u r e , Forest Service, for official use. Daniel L. Cassens
Wallace E. Eslyn
Abstract
The effectiveness of 3-iodo-2-propynyl butyl car­
bamate (IPBC), sodium pentachlorophenate (Na-PCP),
and copper-8-quinolinolate (PQ-8)in prevention of sapstain and mold on freshly cut yellow-poplar and south­
ern yellow pine lumber when bulk-piled or stickered
under field conditions was investigated. Treatment of
all yellow pine lumber and the yellow-poplar lumber
using PQ-8 was completed during late July 1981. All
other yellow-poplar treatments were completed during
late May and early June 1981.The treating and storage
of all lumber was done near the Purdue University
campus, West Lafayette, Indiana.
Na-PCP was the most effective fungicide on bulkpiled yellow-poplar after 8 weeks of exposure followed
closely by 1.5percent, then 0.75 percent IPBC. The best
treatments on bulk-piled yellow-poplar were effective
between 8 and 12weeks. All treatments exhibited supe­
rior protection when applied to bulk-piled southern
yellow pine. After 12 weeks' storage 0.5 percent IPBC
plus 2.0 percent borax, 1.5 percent IPBC, and 1.0 per­
cent Na-PCP treatments were the most effective. Useful
effectiveness of these chemicals on bulk-piled pine did
not carry over to the second summer of storage.
Stickered yellow-poplar was well protected by IPBC for
as long as 46 weeks of exposure; after 67 weeks only the
1.5 percent IPBC provided suitable protection. Stick­
ered southern yellow pine was well protected by all
treatments after 12 weeks, marginally protected after
42 weeks, and not protected after 62 weeks.
The growth of fungal stain and mold on freshly cut
lumber of many species is a serious problem, par­
ticularly during warm, humid months. Sodium pen­
tachlorophenate (Na-PCP) is commonly used to prevent
fungal stain and mold. Since Na-PCP may have adverse
effects on workers and the environment, there is inter­
est in finding fungicides that are equally effective but
52
have a lower mammalian toxicity. Cassens and Eslyn1,2
have reported on the effectiveness of several fungicides
in preventing stain and mold on hardwood and southern
yellow pine lumber under laboratory conditions. One
fungicide, 3-iodo-2-propynl butyl carbamate (IPBC),
looked especially promising. This report presents the
results of tests with IPBC and other selected fungicides
designed to extend the laboratory work to field appli­
cations. Na-PCP was included in the tests as a reference
fungicide.
Materials and methods
Lumber used in the field tests consisted of freshly
cut, roughsawn, yellow-poplar (Liriodendron tulipifera
L.) and southern yellow pine (Pinus sp.) boards 1 by 6
inches by 6 feet long. The lumber contained both sap­
wood and heartwood. The bottom half of each board was
dipped into a chemical solution for 15 seconds. The
Cassens, D. L., and W. E. Eslyn. 1981. Fungicides to prevent
sapstain and mold on hardwood lumber. Forest Prod. J.
31(9):39-42.
2Eslyn,
W. E., and D. L. Cassens. 1983. Laboratory evaluation
of selected fungicides for control of sapstain and mold on
southern pine lumber. Forest Prod. J. 33(4):65-68.
1
The authors are, respectively, Associate Professor of Wood
Products, Dept. of Forestry and Natural Resources, Purdue
Univ., West Lafayette, IN 47907; and Supervisory Research
Plant Pathologist, USDA Forest Serv., Forest Prod. Lab., Mad­
ison, Wis. This publication reports research involving pesti­
cides. It does not contain recommendations for their use, nor
does it imply that the uses here have been registered. All uses of
pesticides must be registered by appropriate state and/or fed­
eral agencies before they can be recommended. Mention of com­
pany or trade names is solely to identify the material used and
should not be interpreted as an endorsement by Purdue Univ. or
the U.S. Dept. of Agriculture. This study was funded in part by
the Forest Prod. Lab. The paper was received for publication in
February 1983 as Journal Paper No. 9311, Purdue Univ. Agri.
Expt. Sta.
Forest Products Research Society 1983.
Forest Prod. J. 33(10):52-56.
OCTOBER
1983
board, still in an upright position, was allowed to drain
for another 15 seconds. The chemicals, sources, and
concentrations used were IPBC (Troy Chemical Corp.,
Inc.) at 0.50, 0.75, 1.0, and 1.5 percent concentration;
IPBC at 0.50 percent concentration plus borax (U.S.
Borax and Chemical Corp.) a t 1.0 and 2.0 percent con­
centration; IPBC at 0.5 percent concentration plus po­
tassium sorbate or KSORB (Monsantoco.) at 1.0percent
concentration; sodium pentachlorophenate (Dow
Chemical Co.) a t 1.0 percent concentration and copper­
8-quinolinolate or PQ-8 (Chapman Chemical Co.) a t
0.054 percent concentration.
After treatment, the lumber was piled into two
stacks for each treatment and species. One stack, 6
boards wide and 12 boards high was constructed using
314-inch-thick sticks for air-drying. The second stack
was bulk-piled and was 6 boards wide and 24 boards
high. The treated portions of the boards were always
placed at the same end of the pile. All piles were kept 8
inches off the ground. An extra course of boards and six
cement cap blocks for weights were placed on top of each
pile. Those piles constructed with sticks also had a
plastic cover. All yellow-poplar lumber was treated and
piled from May 29 to June 16,1981with the exception of
the copper-8-quinolinolate (PQ-8)treatment which was
established on July 30,1981. The yellow pine piles were
erected from July 22 to 28, 1981.
After 4, 8, 12, 16, 46, and 67 weeks of exposure for
the yellow-poplar and 4, 8, 12, 42, and 62 weeks of
exposure for the southern pine the treated and un­
treated portions of the boards were visually scored on
the upper surface as shown below:
0 = stain or mold absent,
1 = stain or mold covers less than 5 percent of
the surface area,
2 = stain or mold covers 5 to 20 percent of the
surface area,
3 = stain or mold covers 20 to 40 percent of
the surface area,
4 = stain or mold covers 40 percent or more of
the surface area.
These categories are, of course, subject to discussion
since it is difficult to quantify a subjective character
such as discoloration of lumber by sapstain and mold.
The amount of discoloration considered objectionable in
one application may be totally acceptable in another. It
was felt, however, that these categories would provide
the reader with a relative feeling for the effectiveness of
each treatment and exposure period. However, some
visual explanation is still required. For example, Figure
1 shows six predominately sapwood southern pine
boards. The untreated ends of each board (top of photo)
were scored “4.” Considering the treated ends, only the
fourth board from the right received a perfect score or
“0.” The board on the far right was scored “2”; the
remainder being scored “1.” One evaluator scored all of
the boards for all exposure periods. The boards were
categorically graded down rather than up in marginal
cases. The least amount of discoloration would result in
a score of “1.” Thus, boards with stain or mold on less
than 5 percent of the surface area (score of “0” or “1”) are
considered essentially stain free or “clean.”
FOREST PRODUCTS JOURNAL
Vol. 33, No. 10
Figure 1. - Condition of southern yellow pine boards treated
(bottom) with 0.50 percent 3-iodo-2-propynyl butyl carbamate
plus 2.0 percent borax compared to nontreated controls (top)
after 17 weeks of exposure.
It is imperative that any fungicide used on lumber
be as effective in stain and mold control as possible.
However, for safety and environmental reasons, it must
be nontoxic to humans who handle the lumber and not
present a serious threat to the aquatic environment
should it be spilled or leached into streams and ponds.
Considering a 160-pound man, the oral LD 50 for NaPCP with 80 percent active ingredient is 14 grams,
IPBC with 17 percent active ingredient is 156 grams,
PQ-8 with 5 percent active ingredient is 108 grams, and
NaCl or salt is 293 grams. The toxicity of the different
fungicides has been reported by Eslyn and Cassens1,2
and is also available from the manufacturers.
Results and discussions
Figures 2 to 9 show the degree of sapstain and mold
on bulk-piled and stickered lumber for both yellowpoplar and southern yellow pine for selected treatments
and exposure periods. Mold and stain were the most
difficult to control on bulk-piled lumber, especially the
yellow-poplar.
53
Bulk-piled yellow-poplar
Figure 2 shows the percent of bulk-piled yellowpoplar boards by treatment which had less than 5 per­
cent of the surface area discolored by mold or stain
(hereafter referred to as “clean”) a t the end of 8 weeks
of exposure. Eighty-six percent of the boards treated
with a 1.0 percent solution of Na-PCP were classified as
clean; all other treatments except a mixture of 0.50
percent IPBC and 1.0 percent KSORB were nearly as
effective. By comparison only 4.0 percent of the control
boards remained clean. Effective protection, however,
ceased somewhere between the 8th and 12th week of
storage. After 12 weeks’ exposure all treatments ceased
to provide satisfactory protection (Fig. 3). At this time
the effectiveness of the different treatments varied sub­
stantially with the 0.75 percent, and higher IPBC
treatments now provided the greatest protection.
Bulk-piled yellow pine
The same treatments used on yellow-poplar were
somewhat more effective when applied to yellow pine.
After 8 weeks of exposure 95 percent or more of the
boards were rated clean for all treatments except 0.50
and 0.75 percent IPBC and 0.054 percent PQ-8 (Fig. 4).
Only 21 percent of the control boards were rated clean.
While all treatments lost some of their effectiveness
after 12 weeks of exposure (Fig. 5), six of them still
provided for 80 percent or more clean boards. Moreover,
96 percent of the boards treated with 0.50 percent IPBC
plus 2.0 percent borax, as compared to only 10 percent
for the controls, were still clean. Figure 1 shows the
effectiveness of this treatment after 17 weeks of ex­
posure (July 24 to November 20,1981). The most effec-
Figure 2. - Percent, by treatment, of bulk-piled yellow-poplar
boards remaining clean or with less than 5 percent stain or
mold after 8 weeks of exposure.
54
Figure 3. - Percent, by treatment, of bulk-piled yellow-poplar
boards remaining clean or with less than 5 percent stain or
mold after 12 weeks of exposure.
Figure 4. - Percent, by treatment, of bulk-piled yellow pine
boards remaining clean or with less than 5 percent stain or
mold after 8 weeks of exposure.
OCTOBER 1983
Figure 5. - Percent, by treatment, of bulk-piled yellow pine
boards remaining clean or with less than 5 percent stain or
mold after 12 weeks of exposure.
Figure 6. - Percent, by treatment, of stickered yellow-poplar
boards remaining clean or with less than 5 percent stain or
mold after 16 weeks of exposure.
Figure 7. - Percent, by treatment, of stickered yellow-poplar
boards remaining clean or with less than 5 percent stain or
mold after 46 weeks of exposure.
Figure 8. - Percent, by treatment, of stickered yellow-poplar
boards remaining clean or with less than 5 percent stain or
mold after 67 weeks of exposure.
FOREST PRODUCTS JOURNAL
Vol. 33, No. 10
55
Figure 9. - Percent, by treatment, of stickered yellow pine
boards remaining clean or with less than 5 percent stain or
mold after 42 weeks of exposure.
tive treatment through 42 weeks of exposure (July 1981
to May 1982)was the 1.5percent IPBC; 61percent of the
treated boards were mostly stain free.
Stickered yellow-poplar
Sapstain and mold were more effectively controlled
on stickered yellow-poplar lumber, regardless of treat­
ment, than on bulk-piled lumber. After 16 weeks or one
full summer of exposure, 91 percent or more of the
boards in each treatment, except 0.5 percent IPBC plus
1.0 percent KSORB, were clean as compared to only 27
percent of the control boards (Fig. 6). After 46 weeks of
exposure (Fig. 7) the effectiveness of a number of treat­
ments began to decline. However, the IPBC treatments
at 0.75, 1.0, and 1.5 percent concentrations still pro­
vided excellent protection. At least 90 percent or more of
the boards in these three treatments remained clean as
56
compared to 73 percent for the Na-PCP treatment and
only 14 percent for the controls. Even after 67 weeks or
two full summers of exposure, 90 percent of the boards
treated with a 1.5 percent solution of IPBC stayed es­
sentially stain free as compared to only 38 percent of
those treated with Na-PCP and 6 percent of the controls
(Fig. 8).
Stickered yellow pine
The effectiveness of the various treatments on
stickered yellow pine was very similar to the results
obtained for yellow-poplar. At the end of the first sum­
mer or after 12 weeks of exposure, 90 percent or more of
the boards in all but the PQ-8 treatment were essen­
tially stain free as compared to only 50 percent of the
control boards. After 42 weeks of exposure (Fig. 9) at
least 70 percent of the surface area of all treated boards
in any treatment were rated clean of fungal dis­
coloration as compared to 32 percent of the controls.
Nearly all of the treatments were equally effective.
After 62 weeks or two summers of exposure, the 1.5
percent IPBC treatment provided the greatest pro­
tection. In this case 66 percent of the boards were still
rated clean as compared to 6 percent for the controls.
Control a t this point was not considered adequate.
Conclusions
All chemical treatments provided good protection
from sapstain and mold on lumber as compared to the
controls. Depending on the chemical and its con­
centration, sapstain and mold can be controlled on bulkpiled yellow-poplar for 8 to 12 weeks, and for an ad­
ditional 4 to 8 weeks on bulk-piled southern yellow pine
when exposed to summer and fall weather conditions in
West Lafayette, Indiana. On stickered yellow-poplar,
good control was achieved through two full summers of
exposure while on yellow pine adequate protection was
lost a t the beginning of the second summer.
The IPBC treatments of 0.75 percent and greater
concentrations or IPBC of 0.50 percent combined with
borax provided as good or better protection than the
common antistain chemical Na-PCP. One exception
does exist. On bulk-piled yellow-poplar after 8 weeks of
exposure, 1.0 percent Na-PCP performed slightly better
t h a n 1.5 percent IPBC. The IPBC, however, out­
performed Na-PCP a t longer exposure times.
OCTOBER
1983