Potential utilization of plant and fungal extracts for wood protection.
Wood is a renewable resource and plays an important role in the world economy; however, it is subject to attack from wood-degrading fungi and insects. Developing effective and low environmental impact technologies for wood protection is imperative. Using natural extractives from plants or microorganisms is an alternative to using synthetic or inorganic chemicals as wood preservatives for wood protection. Extensive research on various plant and microorganism extracts has been conducted in this area worldwide. This article reviews several research projects that explored the utilization of extracts derived from plants or fungi for biological treatment to protect wood or wood products from biodegradation during manufacturing, storage, transportation, and when in service.
Wood is a renewable natural resource used for building construction, and wood production plays an important role in the world economy. Customers often require high-quality wood products, but the value of wood products is often reduced by physical or biological damage. Wood and wood products need to be protected during manufacturing, storage, transportation, and when in service (Uzunovic et al. 2008).
Biological damage to wood and wood products are mainly caused by mold, stain, decay fungi, and insects such as beetles and termites. Protection is generally realized by drying or chemical treatment of wood products. Although relatively low-toxic chemicals are presently used as wood protectants, public concerns remain about the use of these chemicals (Byrne 1998). To develop low environmental impact technologies for the elimination of biological damage is one of the goals of wood protection industry (Freitag et al. 1991).
Utilization of natural extracts from plants or fungi has been explored throughout history and is the root of Chinese medicine and pharmaceutical development in many other countries. Use of these natural extracts to protect wood has also been long recognized, and these natural components were the earliest source of wood preservatives. In ancient times, wood used to build palaces or temples in Asian countries was often impregnated with plant extracts, such as tung oils. These wood structures lasted for several hundreds of years without decay in service. From century to century, however, application of such materials for wood protection was limited worldwide mainly for economical reasons. In the recent century, a variety of inexpensive chemicals have been developed to be used as wood preservatives, but this has retarded the development of the utilization of natural extracts in this area (Freeman et al. 2003).
In recent decades, public attention to the environmental issues of utilization of metal-containing wood preservatives and the disposal problem of chemically treated wood have revived interest in the oldest approach to wood protection--using natural extracts derived from plants or microorganisms (Evans 2003). This paper reviews recent research and the development and utilization of natural extracts for wood protection. It also discusses future opportunities and challenges in the development and use of naturally derived products in this area.
Development of plant extracts for wood protection
The common processes of plant extraction involve three main methods: pyrolysis, solvent extraction, and water extraction. Admittedly, the effectiveness of extracts against targeted pests will be affected by the extraction process. The extraction process and formulation of the final products will not be covered in this paper.
Extracts from bark
Utilization of bark and woodwaste has been a major concern facing the wood industry for a long time. Until now, only a small portion of bark was used in the production of high-value products, and most of the bark was used as fuel or land fill (Harkin and Rowe 1971). Efficient bark utilization can make valuable products out of wood production waste and boost economic development. Bark contains a high tannin, extractive, resin, and wax content. Extraction of bark and woodwaste with the pyrolysis process and its utilization has been studied extensively (Pakdel et al. 1994, Oasmaa et al. 1997, Boucher et al. 2000). Pyrolysis is a thermal degradation process where biomass (bark from sawmills) is broken down into small molecular compounds in absence of oxygen. The nature and yield of the compounds obtained by the pyrolysis process vary depending on the biomass source, moisture content (MC), temperature, and pressure used in the process. Among various potential uses of pyrolytic bio-oils, developing these products as wood preservatives has been the focus of several research organizations (Suzuki et al. 1997, Mourant et al. 2005). These studies showed that bio-oils were effective against fungal growth, and certain phenolic compounds were responsible for fungal inhibition. In one study, a pyrolytic bio-oil was formulated into a phenolformaldehyde resin and used to treat wood blocks of white pine and American beech (Mourant et al. 2007). After exposure of treated wood samples to three decay fungi for 16 weeks in a soil block test, the weight losses of treated wood samples were significantly reduced. Utilization of bio-oils derived from fast pyrolysis of wood feedstocks as wood preservatives was patented by a Canadian company, Ensyn Technology Inc, in the United States (Freel and Graham 2002).
One area which has received considerable attention is the use of tannins extracted from bark and wood of various species as wood preservatives, and a series of patents have been filed in this area (Mitchell and Sleeter 1980, Laks et al. 1988, Lotz and Hollaway 1988, Lotz 1993). Since the 19th century, tannin and tannic acid had been used to improve wood properties and durability. Tannins were mainly extracted from oak bark with hot water, and the wood was soaked in the resultant solution for several weeks as a treatment. Many of these early techniques and patents on using tannins or tannic acid are summarized by Lotz and Hollaway (1988). Tannin extracts are water soluble and difficult to be fixed in wood. During the 20th century, fixation of tannins in wood became a key issue for developing these compounds as commercial wood preservatives. Mitchell and Sleeter (1980) described a method for impregnating wood with a tannic acid (5% in ethanol) followed by a ferric chloride solution (40% aqueous solution). After exposure of wood samples in sea water for 9 months, all of the untreated wood samples were heavily infested with marine borers, whereas none of the samples treated with 5 percent tannic acid and 40 percent ferric chloride complex were infested. Later studies used different levels of tannins (1% to 10%) and fixative metallic salts (1% to 10%) consisting of zinc, copper, aluminum, chromium, or iron against fungal attack. Significantly less weight losses were obtained for all of the treated samples compared with untreated controls (Laks 1988, 1991; Lotz and Hollaway 1988; Lotz 1993).
Bark of various wood species contains different chemical compositions and elements, and bark from some wood species may be more resistant to fungi than others. To address this issue, a study was conducted to evaluate antifungal properties of bark from six wood species: aspen, red maple, yellow birch, balsam fir, white spruce, and white cedar (Yang et al. 2004). Five fungi: Aureobasidium pullulans (de Bary) G. Arnaud, Aspergillus niger Tiegh., Penicillium sp., Gloeophyllum trabeum (Pers.:Fr.) Murrill, and Irpex lacteus (Fr.:Fr.) Fr., representing molds, wood staining, and decay fungi, were used in the test. Based on the colony growth rates of these fungi on bark-extracts-agar media, white spruce (Picea glauca (Moench) Voss.) bark was the best for inhibiting the growth of these fungi, followed by red maple bark (Acer rubrum L.). Red maple wood is known to be very susceptible to decay. White cedar (Thuja occidentalis L.) and balsam fir (Abies balsamea (L.) Mill.) bark provided inhibition only to some fungi tested. Bark of aspen (Populus tremuloides Michx.) and yellow birch (Betula alleghaniensis Britton) possessed little or no inhibition of fungal growth. This study indicated that extracts derived from the bark of a durable wood species, such as white cedar, may not have a higher antifungal property than those extracts derived from the bark of a non-durable wood species, such as white spruce.
Extracts from heartwood of durable wood species
Great variation exists in the durability of different wood species to decay. Certain species such as western redcedar (Thuja plicata Donn ex D. Don), eastern white cedar (Thuja occidentalis L.), yellow cedar (Chamaecyparis nootkatensis (D. Don) Spach), yew (Taxus spp.), redwood (Sequoia spp.), and teak (Tectona grandis Linn.) are well-known for being highly durable wood species due to the presence of extractives in the heartwood. Uses of extracts derived from durable wood species to improve durability of susceptible species have been studied extensively. Purification, identification, and utilization of these extractive chemicals as antifungal agents have been the focus of much research (Nault 1987, DeBell et al. 1999). The resistance of cedars, both western redcedar and eastern white cedar, is attributed to the presence of thujaplicins and thujic acid present in their heartwood and an amount of 0.1 to 0.3 percent of such compounds in the heartwood can be inhibitory to fungal growth (Sowder 1929, Gripenberg 1949, Stirling et al. 2007). In a recent study, 0.5 percent thujaplicin was used in several multicomponent biocide systems with borate and carbon-based biocides. Promising results were obtained for protecting wood from mold, decay, and termite damage (Clausen and Yang 2007).
The extracts of redcedar and yellow cedar have been patented as a protectant of freshly sawn lumber from fungal stain and decay (Chow 1982). In this study, the heartwood of redcedar and yellow cedar was extracted with a borax water solution. The freshly sawn green lumber of softwoods was dip-treated in the extractive solution.
A recent study explored using heartwood extracts of eastern white cedar (Thuja occidentalis L.) to increase aspen strand panel durability (Wan et al. 2007). The heartwood of white cedar was extracted with hot water, and the extracts were freeze-dried into powder. The cedar extracts were added to aspen strand boards either during blending, after forming, or after pressing. The durability tests showed that these panels were mold resistant but not decay resistant. Another study showed that the mold growth was much reduced on aspen panels dip-treated with the extracts of white cedar heartwood at concentrations higher than 5 percent (Yang et al. 2005). No mold growth was detected on panels dip-treated with the extracts at concentrations higher than 5 percent and then brushed with a finishing coating. The decay test showed that dip-treating aspen panels with cedar extracts alone was not effective, but brushing a coating on the top of the treated panels to prevent extracts leaching from the panels significantly increased their durability against brown-rot and white-rot fungi after a standard soil-block decay test.
In addition to the durable wood species listed above, the studies were also extended to many tropical durable wood species in South Africa. One study was conducted in Nigeria on the heartwood extracts from two durable hardwood species, Milicia excelsa (Welw.) C. C. Berg and Erythrophleum suaveolens (Guill. & Perr.) Brenan (Onuorah 2000). In this study, heartwood of these two species was extracted with methanol and impregnated into sapwood of a non-durable wood species. The treated wood blocks were exposed to two decay fungi in a standard soil block test, and the weight loss of these treated samples was significantly reduced compared to untreated controls at dosages of over 48 kg/[m.sup.3].
Extracts from seed, fruit, and herbaceous plants
The potential of using extracts derived from herbaceous plants, seeds, or fruit wastes, so-called essential oils, to protect wood against degrading fungi and insects has received much attention worldwide (Vanneste et al. 2002, Maoz et al. 2007). Among various extracts from herbaceous plants, cinnamon extracts have shown excellent antibacterial, antifungal, and antitermite properties and have potential as a commercial wood preservative (Cheng et al. 2006, Lin et al. 2007, Maoz et al. 2007). The effective compound of cinnamon leaf extracts was identified as cinnamaldehyde, and wood treated with this compound showed excellent decay and termite resistance in laboratory exposure tests in Taiwan (Lin et al. 2007). The results of this study showed that weight losses on non-treated wood decayed by the brown-rot and white-rot were 31.8 percent and 18.7 percent, respectively. Samples treated with 5 percent of cinnamon extracts were 0.8 percent and 1.2 percent. For termite resistance, the average weight loss of non-treated wood samples caused by termite infestation was 7.28 percent, whereas those samples treated with 5 percent of cinnamon extracts was 1.35 percent.
One of the earliest commercially available wood protectants was linseed oil derived from seeds of flax (Linum spp.) (Flax Council of Canada, Winnipeg, Canada). Linseed oil is a primary ingredient in many oil paints, varnishes, and stains, and it provides superior protection on wood surfaces, from decks to marine products. Linseed oil alone, however, is vulnerable to mold infection, and it is most often mixed with other natural extracts such as tung oil or orange peel turpentine, or with mild fungicides such as borate. A recent study showed that a combination of boric acid with linseed oil has good potential for increasing boron retention, reducing leachability, and improving efficacy of the product against termites (Lyon et al. 2007)
Antifungal compounds were also found in some fruit peels and extracted as potential ingredients for new wood preservatives. One such example is the evaluation of essential oils derived from the fruit peels of different citrus fruits and oranges (Macias et al. 2005). Volatile constituents and flavonoids of extracts of citrus fruits have been suggested to act as pesticides against fungi and insects.
Plant extracts were also tested for controlling nematodes. A broad screening of antinematode activity of some native plant extracts against the pine wood nematode (Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle) was conducted in Malaysia (Mackeen et al. 1997). In this study, 79 Malaysian plants from 42 families were extracted with methanol and tested for their antinematode activity against the pine wood nematode by a fungal-feeding assay. The results showed that extracts (2% in ethanol) from 27 plants demonstrated activity against this nematode, while the remaining 52 species were inactive. Among the active plant extracts, five of them were strong active, seven low active, and the remainder were moderate.
Development of fungal extracts for wood protection
There are three direct mechanisms for biological control of one microorganism by another: parasitism, antibiosis, and competition (Baker 1991). The utilization of fungal extracts for wood protection is mainly involved in those fungi with antibiosis mechanisms; that antagonists secrete metabolites harmful to other organisms. Since the discovery and development of antibiotics in the beginning of the 20th century, many antibacterial, antifungal, insecticidal, and herbicidal products have been obtained from fungal metabolites and used for crop protection in the agricultural sector (Butt et al. 2001). The development of fungal extracts for wood protection, however, has only been explored to a limited extent.
The main process for fungal extraction involves solvent extraction with methanol, chloroform, or ethanol. But, extraction can be done from fungal biomass or from fungal culturing medium, which is different than plant extraction.
Fungal extracts for controlling tree disease and insect damage
Many fungi produce antibiotic compounds and these compounds can be used as antimicrobial agents against plant, animal, and human disease. Development of fungicides from fungal metabolites has become a new perspective in the biological control of plant and tree diseases (Okeke et al. 1992). An early study was conduced to extract and identify antibiotics from culture filtrates of several species of Trichoderma for controlling tree pathogen, including Heterobasidion annosum (Fr.:Fr.) Bref., a pathogen of pine trees (Dennis and Webster 1971). In this study, a trichodermin was identified from the chloroform extract and a peptide antibiotic was obtained from the ethanol extract. These fungal extracts were biologically active against H. annosum.
Using Phaeotheca dimorphospora and its metabolites to control various tree diseases is another example. P. dimorphospora was originally isolated from elm wood (DesRochers and Ouellette 1994), and this fungus had demonstrated strong antagonistic activity against many parasitic and saprophytic fungi in vitro and in hardwood and softwood seedlings (Yang et al. 1993). The main functional compound produced by this fungus was identified as salicylic acid.
Fungi not only produce toxic compounds in the metabolites that directly inhibit growth from other fungi, they also produce some non-toxic compounds (glycoprotein so-called elicitors) that have no direct function on other fungi but can induce trees to produce phytoalexins against invasion from pathogens. This mode of reaction is unique for living trees; when trees were cut, they immediately lost this ability. One good example of using this kind of fungal metabolites is a patented technology for controlling Dutch elm disease (Hubbes 2000). In this patent, a non-toxic and heat stable compound (glycoprotein) was isolated from the culture filtrate of a non-aggressive strain of Ophiostoma ulmi (Buisman) Nannf. This compound was injected into the stem of trees or seedlings of the American elm (Ulmus americana L.) that is susceptible to Dutch elm disease. The compound induced the elm to produce several mansonones (phytoalexins) for increasing resistance against Dutch elm disease. The practice had been successful in both green house and field tests.
Fungal extracts were also explored to control heartwood white-rot of rubber trees (Hevea brasiliensis (Willd. ex Adr. Juss.) Muell. Arg.) caused by Rigidoporus lignosus (Klotzsch) Imazeki (Idwan Sudirman et al. 1992). In this study, antibiotic substances were extracted from the culture medium of Lentinus squarrosulus (Mont) Singer with butanol. The antifungal activity of the extract was tested against R. lignosus, and the inhibitory effect and thermo stability of this extract was observed.
Fungal extracts can not only be used for controlling tree diseases, but also as insecticides against insect damage in trees. A representative study was conducted in the University of New Brunswick in Canada (Calhoun et al. 1992). In this study, numerous fungal species were screened for the production of metabolites toxic to spruce budworm (Choristoneura Jumiferana (Clemens) larvae. The results showed that one isolate of Phyllosticta sp. and two isolates of Hormonema dematioides Lagerberg & Melin yielded extractable compounds that resulted in the mortality of the insect larvae.
Fungal extracts for preventing wood stain and decay
Decay and stain are two most important problems limiting the utilization of wood and wood products. One of pioneering studies on utilization of fungal metabolites for wood protection was conducted in the 1960s and 1970s on a species of Scytalidium, which was isolated from a sound Douglas-fir pole and showed growth inhibition of decay fungi (Ricard et al. 1969). The antifungal compounds produced by Scytalidium were identified as scytalidin and scytalidic acid (Strunz et al. 1972, Overeem and Mackor 1973). These compounds were easy to isolate from the metabolites of growing colonies of Scytalidium. Most decay and staining fungi were sensitive to scytalidin (Stilwell et al. 1973). Later, Stranks (1976) showed that the antibiotic scytalidin, produced by Scytalidium isolates, as well as several other antibiotics were capable of inhibiting sapstain in pine wood. These studies demonstrated the potential of using fungal metabolites as wood preservatives against stain and decay.
Several studies have used Trichoderma spp. as possible control agents for wood decay fungi since the 1970s (Highley and Ricard 1988, Freitag et al. 1991.). Extensive study was also conducted to examine the inhibitory activity of metabolites produced by different species of Trichoderma, Penicillium, and Aspergillus against a range of decay fungi (Bruce and Highley 1991). The results of these studies showed that the filtrates of most isolates produced varying degrees of inhibition against different decay fungi, the extent of control varied widely. The effect of culture filtrates of these antagonists on the growth of decay fungi showed no correlation to their antagonistic abilities in interaction studies with decay fungi. The studies also demonstrated that the metabolites produced by Trichoderma species were more effective against brown-rot fungi, whereas the Aspergillus filtrate was more effective against white-rot Basidiomycetes.
In another study, the crude filter-sterilized culture filtrate of Trichoderma (Gliocladium) virens Miller, Giddens & Foster was vacuum impregnated to southern pine wood blocks and then subjected to three white-rot and three brown-rot fungi in a soil-block test (Highley 1997). The results showed that the culture filtrate of T. virens had fungistatic effect against the decay fungi in agar medium, but weight loss of treated wood blocks was only slightly reduced. The effective antifungal compounds produced by this fungus were identified as gliovirin and gliotoxin, but no further purification and dose response of these compounds were done in the study.
A successful example of using crude culture metabolites to control weight loss caused by decay fungi was reported by using a mutant strain SC-36 of Streptomyces rimosus Sobin, Finlay & Kane (Croan 1997). In this study, crude metabolites presented in the culture medium of S. rimosus were collected and tested against a range of decay fungi. The results showed that the growth of all of the tested fungi was inhibited by this crude preparation. Wood blocks pressure treated with diluted (0.25x) or undiluted (1x) crude culture metabolites were decay resistant in a soil block test. In a field trial, green log section and wood sticks of pine and maple dip-treated with concentrated crude culture metabolites (10x) inhibited growth of all of the wood-inhabiting fungi. This crude culture metabolite preparation from SC-36 of S. rimosus was claimed as an environmentally benign biological wood preservative.
A number of fungal metabolites were tested to control sapstain of radiata pine (Pinus radiata D. Don) in New Zealand (Vanneste et al. 2002). Among the different compounds tested, massoialactone (dihydro-5-hexyl-2H-furan-2-one) produced by a Trichoderma species was the most effective. In a laboratory test, 10 percent of massoialactone emulsion completely prevented growth of sapstain fungi on radiata pine. In a field testing period of 108 days, wood blocks of P. radiata dip-treated in a 10 percent massoialactone emulsion developed less sapstain than those blocks treated with a currently used commercial antisapstain chemical NP-1. In another study conducted in Canada, two fungitoxic compounds identified as trichodermin and trichodermol were isolated from a fungal culture filtrate of Stachybotrys cylindrospora C.N. Jensen (Hiratsuka et al. 1994). These compounds significantly inhibited the growth of a major blue-stain fungus, Ophiostoma crassivaginatum (H.D. Griffin) T.C. Harrington, on aspen chips, and can be considered as candidates for bio-protection of aspen wood and its products from fungal stain.
Metabolites produced by antibiotic-producing organisms not only have potential for preventing wood stain and decay, but also for removing stain from wood after infection. One study was conducted by Croan and Highley (1996) to examine the use of fungal metabolites from two white-rot fungi, Bjerkandera adusta (Willd.:Fr.) P. Karst and Talaromyces flavus (Klocker) A.C. Stolk & R.A. Samson, in removing stain on sap-stained pine wood. The results were promising, and it was claimed that the combination of metabolites produced by the two antagonists removed sapstain and killed existing fungal growth.
Fungal extracts for improving durability of composites
Wood-based composites, including different types of panels, are being increasingly utilized as the principal framing elements in building construction throughout the world. Exposure of these materials to wet or humid environments may cause infestation by molds and decay fungi. Use of natural extracts to improve the durability of composites is an attractive alternative to other protection approaches, even though limited studies have been conducted to protect panels with fungal extracts. Recently FPInnovations--Forintek Division in Canada tested the ability of extracts of Phaeotheca dimorphospora DesRochers & Ouellette to suppress the growth of various molds and decay fungi in vitro and evaluated the possibility of using extracts of P. dimorphospora to treat oriented strandboard (OSB) panels and reduce mold infection of the panels when wetting occurs (Yang et al. 2007). In this study, culture metabolites of P. dimorphospora were extracted, and the antibiotic activity of the extracts was tested in Petri plates against various molds and decay fungi. The OSB panels were then dip-treated with the extracts and exposed to a humid environment for mold growth testing for a period of 8 weeks. The results showed that the mycelial growth of all of the fungi tested (mold and white-rot and brown-rot fungi) was inhibited by the extracts of P. dimorphospora on agar plates. Panel samples dipped with the fungal extracts (5% in acetone) showed little mold growth, whereas untreated control panels were seriously affected by various molds. This study demonstrated a high potential for utilization of fungal extracts for protection of composite panels against mold and decay.
Opportunities and challenges
The recent withdrawal or restricted use of a number of key synthetic pesticides and wood preservatives has created a critical need for safe alternatives. The requirement of biological-based technologies and products has been recognized universally as an alternative to synthetic or inorganic pesticides. This recognition may accelerate research and development in this area and may lead to the more rapid formulation and commercialization of biologically based products. But, it must be recognized that some bio-based chemicals can be as dangerous as synthetic ones and caution must be exercised when promoting such products.
Biocontrol agents are increasingly being used as alternatives to chemical pesticides. Several different approaches are being developed for biocontrol of wood stain and decay. In some countries, research is based on improved production systems for bio-pesticides and improved strains through selection or genetic engineering. With biotechnology tools, production could be less expensive and formulations more effective. Transgenic bio-pesticides may prove faster-acting and broader-spectrum than conventional products, but public attitudes against the environmental release of genetically engineered organisms may have a strong impact on the development of these products. This public perception, however, may have minimal impact on the utilization of extracts derived from these organisms.
One of the major hurdles in registration and commercialization of fungal biological control agents is risk assessment. The particular concern of using these biocontrol agents is the production of mycotoxins by these fungi to contaminate food, which in turn, cause human disease. For example, an antibiotic metabolite produced by Penicillium urtica Bainier was identified as patulin that can suppress damping-off disease of several plants. Patulin, however, is a mycotoxin and its carcinogenic effect is as important as some synthetic chemical pesticides. Some mycotoxins have been found in fungal affected outdoor softwood (Land and Hult 1987). Using fungal extracts as wood protectants can eliminate the known harmful mycotoxins from fungal metabolites and avoid wood and food contamination by the toxic compounds produced by the biocontrol microorganisms.
Predictable effective performance is essential to any new product put on the market. One of the major shortcomings of biological control agents is the lack of consistent pest control effectiveness. Living microbial biocontrol agents are influenced more by environmental conditions than chemicals; therefore, using functional extracts of plants or fungi can overcome this weakness of bio-pesticides and make them more stable for pest control efficacy.
For over a half of a century, most research on the biological control of pests in agriculture has concentrated on the use of a single selected biocontrol agent to combat a single pest. This approach has led to the successful development of some commercial biocontrol products; however, in most cases, the biocontrol products failed in field trials, especially for wood protection that involved a range of pathogens. Over the last 10 years, greater emphasis has been given to biocontrol approaches that include mixtures of biocontrol agents and integrated biocontrol strategies. This novel approach may lead to a wider spectrum of activity of the biocontrol agents and an increase in the efficacy and consistency of the biological treatment. Development of natural extracts as pesticides should also follow this novel approach with combinations of different extracts into one product. Chinese medicine rarely used extracts from a signal plant for curing a human disease, it is always from a mixture. It will be a great challenge, however, for the strategic selection of synergistic mixtures.
A major challenge for the wood industry in developing and using living organism-derived products or processes for wood protection is registration of the bio-products. Unlike synthetic chemical wood preservatives, the effective ingredients in natural extracts are often a mixture of several or dozens of compounds; purification, identification, and quantification of these compounds are time and resource consuming. Registration of this type of pesticide requires various complex tests on the product, cost is very high, and processing time is long. These regulatory barriers deter companies from innovations in new types of wood preservatives and creating commercial products.
Most of the previous studies on natural extracts for wood protection depended on their antibiotic or toxic mode of action to other organisms. Future research in this area should focus on non-toxic modes of action of the potential products, such as natural compounds acting as elicitors, regulators, inhibitors, enzymes, or repellents for pest control. Recently, the Pest Management Regulatory Agent (PMRA) in Canada proposed a fast registration scheme to boost registration of low-risk pest control products in Canada. The proposed framework covers two broad types of products: low-risk biochemicals which includes the naturally occurring substances mentioned previously and non-conventional pesticides that include certain types of plant and fungal extracts and essential oils. To qualify for this fast registration stream, products should possess low inherent toxicity to non-targets, low environmental persistence, and have a non-toxic mode of action.
Another major concern of utilization of potential natural extracts derived from plants is relied on sufficient, inexpensive biomass for production. Since most naturally durable wood species grow slowly and were over-cut in the past, the availability of these trees has declined dramatically and the decline continues. Some tropical durable wood species are limited in some remote regions and have little commercial value as a source of extracts. Extracts with high commercial value as wood preservatives will more likely come from the common by-products of forest or agriculture operations.
Many plant or fungal extracts are not water soluble; using a chemical solvent as a carrier of ingredients will create environmental problems and increase the cost of the products. Formulation of natural extracts as effective water soluble or emulsified products is a key issue for commercialization. Protection of wood products against damage from wood-degrading fungi is essential from a sustainable development perspective, environmentally and economically. The methods used to control wood deterioration must be effective without having a negative impact on the environment and public health. Utilization of natural extracts may play a key role in wood pest management in the future. The benefit, however, can be obtained only when this technology is used in a commercial product. Future development on utilization of natural extracts as wood preservatives will rely on the market requirement, the treated wood use policy, the speed of registration, and the cost of commercialization.
This paper summarizes various promising potential biological treatments with extracts derived from various plants and antagonistic fungi for protecting wood and its products against infestation from mold, decay, insect, and nematode. In general, studies conducted in the past showed that development of botanical pesticides as a friendly natural alterative to inorganic or synthetic chemical wood preservatives is feasible and promising. But, the current market requirements on wood preservatives, low production cost, and long-term efficacy make this types of products unable to compete with existing synthetic chemicals. In addition, many challenges exist in the registration and commercialization of these potential products.
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The author is a Senior Research Scientist, FPInnovations--Forintek Division, Quebec, QC, Canada (firstname.lastname@example.org). This paper was received for publication in August 2008. Article No. 10521.
Dian-Qing Yang, Forest Products Society Member.
[c] Forest Products Society 2009.
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|Date:||Apr 1, 2009|
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