EVALUATION OF FUMIGANTS FOR DECAY CONTROL IN RED AND WHITE OAK TIMBERS. by T.L. HIGHLEY *

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1 EVALUATION OF FUMIGANTS FOR DECAY CONTROL IN RED AND WHITE OAK TIMBERS. by T.L. HIGHLEY * Keywords:- Fumigation: Wood decay Basamid: Metham sodium: Chloropicrin: Methylisothiocyanate: Red Oak: White Oak. situations conducive to decay. This study describes the movement and persistence of four fumigants in sawn red and white oak timbers exposed without ground contact. Abstract This study describes the movement and persistence of four fumigants in sawn red and white oak timbers exposed without ground contact for 2 years in Madison, Wisconsin, USA. Chloropicrin moved the farthest from the point of application; metham sodium moved next farthest, followed by Basamid. Methylisothiocyanate (MIT), applied as pellets, was not effective. This was probably because MIT was lost from pellets prior to treatment Chloropicrin and metham sodium moved farther and persisted longer in red oak than in white oak. Basamid also moved farther in red oak, but persistence was the same in both species. Wrapping the timbers with 0.15 mm polyethylene prior to treatment enhanced the distance chloropicrin and metham sodium moved in both red oak and white oak. Introduction Numerous studies have shown that fumigants effectively eradicate decay in softwood poles, piling and large sawn timbers (Morrell and Corden, 1986; Morrell, 1989). However, except for a few reports on treatment of oak logs with fumigants to eradicate the oak-wilt fungus (Partridge, 1961; Jones, 1963; Schmidt et al., 1982), no reports describe the effectiveness of fumigants in eradicating decay in hardwood species exposed under field conditions. However, Morrell et al. (1992) reported preliminary laboratory evaluation of fumigant treatment of several hardwood species. Their results indicate that fumigants move to varying degrees through the hardwoods tested. Fumigant efficacy in hardwoods is needed because increased emphasis on hardwood utilisation will result in increased use of hardwoods in * USDA Forest Products Laboratory, One Gifford Pinchot Drive, Madison, Wisconsin , USA. Materials and Methods Movement of chloropicrin (trichloro- nitromethane), metham sodium (32.1 percent sodium-nmethyldithiocarbamate), methyliso- thiocyanate (MIT) pellets (Degussa, Germany, and Basamid (tetrahydro-3,5-dimethyl -2H-1,3,5-thiadiazine-2- thione, also known as Mylone or Dazomet) (Hopkins, Madison, Wisconsin) through timbers was evaluated by open- and closed-tube bioassays (Scheffer et al., 1982, Highley and Eslyn, 1989a and b). The MIT pellets originally contained 60 percent MIT, but this percentage declines with storage (Morrell, personal communication). Both metham sodium and Basamid must decompose to MIT to effectively control decay fungi in wood Treatment of Test Timbers For this study, 16 white oak and 16 red oak timbers (Quercus sp.), 152 mm x 152 mm x 4.26 m (6 in. x 6 in. x 14 ft), were used. The initial moisture content of all timbers was above 30 percent and remained above 30 percent for the duration of the study. Fumigation holes 25.4 mm in diameter and 127 mm deep were drilled in a cluster at about the centre line of each timber on the upper surface. The number of treatment holes varied somewhat with the amount of fumigant applied to a given timber. One-half of the timbers fumigated with chloropicrin or metham sodium were wrapped with 0.15 mm polyethylene prior to fumigation. The ends of the timbers were not covered. To enhance release of fungistat, 20 ml of water was added to MIT treatment holes and 20 ml of 1 percent NaOH was added to Basamid treatment holes (Morrell et al., 1988). Timbers received 270 ml of chloropicrin, 470 ml of metham sodium, 175 g of Basamid, or 100 g of MIT, these amounts having been indicated by previous experimmtation. Holes were plugged with rubber stoppers. 17

2 Test Fungi The brown-rot fungus Postia placenta (Fr.) M.J. Lars, et Lomb. (MAD-698) and the white-rot fungus Trametes versicolor (L.:Fr.) (MAD-697) were used as test organisms to the open-tube bioassays. The brown-rot fungus Gloeophyllum trabeum (Pers.:Fr.) Murr. (MAD-617) was used in the closed-tube bioassays. Open-Tube Bioassay Screwtop test tubes (16 X 125 mm) retaining malt agar were inoculated with the teat fungi and incubated until growth was well established. A white pine (Pinus strobus, L.) stick (4.7 x 4.7 x 25.4 mm), previously soaked in distilled water and steam sterilised was then placed into each tube. The tubes were incubated again until the fungi became established in the sticks. Three sets of four holes each were drilled at distances of 0.30, 0.61, and 1.22 m from centre line in both directions on the opposite face from the fumigation holes. These inoculation holes were 25.4 mm in diameter and 25.4 mm deep. A screwtop test tube cap with a hole drilled in the centre was glued into each of the inoculation holes to receive the inoculation tubes. Each of the four holes in one line (at 0.30,0.61, and 1.22 m from the centre line) was inoculated with the same fungus. The three lines of holes to the left of the centre line received a different fungus from the holes to the right of the centre line. For example, the holes 0.30, 0.61, and 1.22 m to the left of the centre line were inoculated with P. placenta, and the holes to the right of the centre line were inoculated with T. versicolor. Closed-tube Bioassay The presence of residual fumigant in the timbers was assessed using a closed-tube bioassay with the wood-decay fungus G. trabeum. Increment cores 12 cm long were taken from the timbers at 0.30,0.61, and 1.22 m from the fumigation holes and immediately placed into screwtop test tubes (16 x 150 mm). The tubes were returned to the laboratory and the cores placed into screwtop tubes containing malt-agar slopes inoculated with G. trabeum. The tubes were incubated at 27 C and 70 percent relative humidity until growth of the assay fungus in tubes containing untreated cores (controls) reached the end of the tubes. Inhibition of fungal growth compared with that in control tubes was used as the measure of residual fumigant Timber Exposure The timbers were exposed at the Valley View Exposure Site near Madison, Wisconsin, on racks to elevate them above ground. Timbers were placed with screwtop test tubes facing down to protect the cultures from the sun. Inspections Screwtop test tubes with inoculum were removed at 1, 4, 13, and 25 months. Fresh cultures were inserted into timbers 1 month prior to each removal. After removal, the test tubes were transferred to the laboratory where each decayed wood stick was transplanted to a fresh tube of malt agar. These tubes were incubated at 27 C for 6 weeks to determine whether the test fungi remained viable or had been killed, presumably by the fumigant. Controls (test tubes in non-fumigated timbers) were all replaced at each inspection to ensure that the fungi remained viable during their incubation in the field. Increment cores for closed-tube bioassays were removed 4 months, 1 year, or 2 years after treatment. Results Open-Tube Bioassay Data concerning the fungistatic effect of the fumigants against decay fungi implanted into the red oak and white oak timbers at intervals throughout the 24 month test period are given in Tables 1 and 2. All cultures implanted in the control timbers survived the l-month incubation periods. Methylisothiocyanate applied as pellets was not inhibitory to the implanted fungi in either red or white oak timbers; these data are not shown in the Tables. Red Oak The chloropicrin treatment combined with wrapping timbers in polyethylene most effectively killed fungi implanted in red oak (Table 1). This treatment resulted in almost 100 percent kill 0.30, 0.61, and 1.22 m from the centre line throughout the 24 month test period. The chloropicrin treatment was less effective in timbers which were not wrapped. Most cultures implanted in the non-wrapped timbers were killed 0.30 m from the centre line, but efficacy declined at 0.61 m and few cultures were killed at 1.22 m. By 12 months, efficacy of chloropicrin at 18

3 killing the implanted fungi in the non-wrapped red oak timbers declined at all distances from the centre line. Table 1 Viability of fungal culters after fumigation of red oak timbers However, efficacy decreased considerably at 3 months, and most cultures were viable at 12 months. Metham sodium treatment with wrapping followed chloropicrin closely in effectiveness at killing fungal cultures implanted at time of treatment. Like chloropicrin, treatment effectiveness decreased thereafter, and fungistatic effect was virtually nil at 24 months. Neither chloropicrin nor metham sodium were as effective at killing fungal cultures in non-wrapped white oak timbers. Table 2 Viability of fungal cultures after fumigation of white oak timbers Wrapping also enhanced the effectiveness of metham sodium at killing the implanted fungi in red oak (Table 1). Most cultures implanted in wrapped timbers immediately after treatment and removed 1 month later were killed at all distances from the centre line. However, efficacy of metham sodium decreased in the red oak timbers at 3 months. In the non-wrapped timbers, metham sodium killed almost all cultures implanted 0.30 m from the centre line at the time of treatment. However, like the wrapped timbers, efficacy declined at 3 months. Most cultures implanted 0.30 m from the centre line in red oak timbers treated with Basamid were killed, but most cultures were still viable at 0.61 and 1.22 m. White Oak The fumigation treatrnemts were not as effective at killing the implanted fungi in white oak as in red oak (Table 2).Like red oak the most effective treatment in killing implanted fungi was chloropicrin in wrapped timbers. Virtually all cultures implanted at the time of treatment and removed 1 month later were killed at 0.30, 0.61, and 1.22 m from the centre line. Basamid was effetive only at 0.30 m from the centre line, but effectiveness varied between the two timbers receiving treatment. Basamid moved more slowly than the other treatments in white oak but efficacy persisted longer at 24 months, most cultures 0.30 m from the centre line were killed. Closed-Tube Bioassay Bioassays of cores removed from red oak to determine residual fungitoxicity generally indicated similar fungitoxicity as that observed with the implanted fungi (Table 3) Fungitoxicity determined by bioassays of cores timbers differed somewhat determined by implanted fungi. removed from white oak from fungitoxicity At 4 months, residual 19

4 fungistatic effects were detected 0.30, 0.61, and 1.22 m from the centre line in chloropicrin- and metham sodium-treated white oak timbers, (Table 3). No residual fungistatic effect was detected in MIT-treated white oak timbers at 4 months. Fungistatic effect for all treatments in the white oak timbers generally decreased by 12 months. Discussion The ineffectiveness of MIT pellets in this study was surprising considering the success of this material in other formulations in eradicating decay fungi from wood (Helsing et al., 1984; Morrell et al., 1990). In previous work MIT pellets performed well in Douglas-fir and Southern Pine timbers (Highley and Eslyn, 1989a; Highley, 1991a). Morrell (personal communication) conducted analyses of MIT in pellets and found that the concentration of MIT decreased during storage. Loss of MIT from pellets prior to application probably explains the lack of effectiveness of MIT in the oak timbers in this study. Table 3 Growth of Gloeophyllum trabeum in tubes containing cores removed from red oak and white oak timbers at intervals after fumigation. Figure 1. Comparative viability of fungi in non-wrapped red oak and white oak timbers, 0.61 m from the point of fumigant introduction, months after treatment. At each distance from the centre line the fumigants exhibited a higher level of fungitoxicity in red oak than in white oak (Figure 1). Perhaps tyloses present in the vessel elements of white oak restricted chemical movement. The data on the viability of Trametes and Postia 0.61m from the fumigation point, one month after application, in both red oak and white oak (Figure 2) reveals that, in general, chloropicrin produced Figure 2. Effect of fumigants on viability of P.placenta and T. versicolor, 0.61m from the point of fumigant introduction, 0-1 month after treatment. 20

5 greatest inhibition of growth, and Basamid the least. Given that previous experimentation had indicated that the different quantities of material applied all had equivalent toxicity potential, this observation is taken to indicate that Chloropicrin moved farthest, followed by metham sodium and finally Basamid. This is similar to results previously obtained in tests with softwoods (Highley 1986, 1991a). The distance moved was also similar to that observed in softwoods. Movement of metham sodium decomposition products in red oak timbers however was better than observed in earlier studies with softwoods (Highley, 1986; 199la). This may be because of better decomposition of metham sodium in hardwoods (Morrell, 1992). Basamid decomposition products moved about the same as observed in softwoods (Highley 1991b). Basamid decomposes slowly to MIT in wood. Morrell et al. (1988) found that high ph enhanced decomposition. However, addition of NaOH to treatment holes appeared not to improve movements in the oak timbers. Recently, Forsyth and Morrell (1992) found that copper increased efficiency of breakdown of Basamid to MIT. 1989). Previously, Highley and Eslyn (1989a and b) found that in permeable species such as Southern Pine (mostly sapwood) fumigants provided shorter protective periods than in impermeable species, such as Douglas-fir (mostly heartwood). The type of extractives present in the different species might also contribute to differences in the retention of fumigants. Red oak and Douglas-fir contain more polar phenolic compounds (tannins, lignins, and flavonoids) than does Southern Pine. Chloropicrin and metham sodium may remain longer in wood containing polar phenolic compounds because polar nitro groups in chloropicrin and polar dithio groups in metham sodium can form a strong hydrogen bond with polar phenolic compounds. White oak also contains considerable quantities of extractives, but they are different from those in red oak. In an earlier study, Highley and Eslyn (1989b) found that wrapping non-pressure-treated Southern Pine timbers prior to application of fumigant enhanced the movement and persistence of the fumigant. Likewise, Goodell et al (1980) found that wrapping an untreated Southern Pine laminated arch in polyethylene sheeting prevented loss of chloropicrin from the wood surface. Graham (1973) reported that wrapping creosoted Douglas-fir poles to retard loss of fumigant was unnecessary. Presumably the envelope of preservative-treatment was sufficient to restricted loss of the fumigant. Wrapping also may not be a benefit to fumigant efficacy in non-pressure-treated Douglas-fir timbers; Highley (1986) and Highley and Eslyn, (1989a and b) found that fumigants performed Figure 3. Effect of Chloropicrin and Metham sodium on viability of P. placenta in wrapped red oak and white oak 0.61 m from the point of fumigant introduction at the times indicated. Unexpectedly, Chloropicrin and metham sodium persisted longer in the red oak timbers than in the white oak (Figure 3). Because red oak is more permeable than white oak it was expected that red oak might lose chemical more rapidly and the duration of effectiveness in this species (Morrell, Figure 4. Viability of T. versicolor in wrapped and non-wrapped read oak and white oak 0-1 month after fumigant introduction. 21

similarly in pressure-treated and non-pressure-treated Douglas-fir timbers.

moved in both red and white oak (Figure 4).

some cases, on whether the timbers have been pressure treated.

Metham sodium moved second farthest and then Basamid.

6 similarly in pressure-treated and non-pressure-treated Douglas-fir timbers. In the present study, wrapping untreated timbers prior to fumigation enhanced the distance chloropicrin and metham sodium moved in both red and white oak (Figure 4). Persistence of fumigant was usually also improved in wrapped red oak but was not so consistently improved by wrapping white oak.. Thus, the beneficial effects of wrapping on fumigant performance appear to depend on both the timber species and, in some cases, on whether the timbers have been pressure treated. Conclusions Chloropicrin moved farthest of the four treatments from point of application. Metham sodium moved second farthest and then Basamid. Methylisothiocyanate pellets were ineffective, probably because MIT was lost from pellets prior to treatment. Fungitoxic concentrations of chloropicrin and metham sodium vapours remained in red oak longer than in white oak. Basamid persisted equally well in both species. Wrapping enhanced movement and persistence of chloropicrin and metham sodium in both species. Chloropicrin and metham sodium also persisted longer in wrapped red oak timbers, but wrapping did not so consistently improve persistence in white oak. REFERENCES 22

Regarding the code-compliance of CCA treated laminated veneer lumber

Determination 2015/079 Regarding the code-compliance of CCA treated laminated veneer lumber Summary This determination discusses the pathway to establishing compliance with Clause B2.3.1 for laminated