Southern Exposure: Long-Term Field Testing of Wood Protectants

When researchers are looking to evaluate the performance of wood protectants, the harsher the environment the better. Which is why Forest Products Laboratory (FPL) researchers put specimens to the test in the Harrison Experimental Forest (HEF) in Saucier, Mississippi, and have been doing so for 80 years.

Generations of FPL researchers have used the HEF field site for sub-tropical field testing. Here Oscar Blew is rating posts at the HEF (1950’s).

Located about 35 miles north of the Gulf of Mexico, this sub-tropical field site receives about 60 inches of rainfall a year and has a mean temperature of 68 degrees Fahrenheit. The wood decay hazard in this area is rated “severe” according to the American Wood Protection Association Use Class Rating System and there is significant subterranean termite activity. When in ground contact, untreated wood rarely lasts 12 months in the HEF, to which researchers respond “challenge accepted.” Continue reading

Time in a Bottle: Finding New Life for an Old (Yet Reliable) Test Method

The simple soil bottle presents an extremely useful tool for predicting performance of preservative treated, modified or naturally durable woods. The methodology was developed in the 1940s exclusively for evaluating wood preservatives against wood decay fungi. It has been adapted over several decades to include naturally durable woods, wood plastic composites, and engineered wood products, and we use it constantly here at the Forest Products Laboratory (FPL).

The basic premise of the soil bottle is a material is presented to an actively growing fungus in an otherwise sterile environment. The resistance of the material to fungal degradation is determined by comparison to reference materials (non-durable species or treated reference material). The soil bottle also presents an excellent tool for studying basic fungal biology whereby cellular changes in wood during the decomposition process can be analyzed.  The soil presents a refuge for the decay fungus as well as a source for moisture and transported ions relevant to the decay process.

Past, present and future research at FPL is looking at ways of modifying the standard soil bottle setup to be even more useful for the evaluation of wood and wood protectants. Here are just a few examples of where FPL researchers are pushing the boundaries of the standard soil bottle: Continue reading

Warm, Wet Wood Means Fungi to Follow: Is Your Home a Mushroom Magnet?


Climate index for decay hazard. Higher numbers indicate greater hazard.

Fungi are the principal agents of decomposition in ecological systems, and are an unavoidable fact-of-life. Although particularly prevalent in the south, where temperature and humidity create ideal conditions, wherever you find organic matter, fungi will be close behind.

When it comes to wood and wooden structures however, these pint-sized parasites can create big problems, leaving unsightly stains or even weakening buildings to the point of structural failure.

Two kinds of major decay fungi are recognized: brown rot and white rot. With brown-rot fungi, only the cellulose is extensively removed, the wood takes on a browner color, and it can crack across the grain, shrink, collapse, and be crushed into powder.


Representative samples of four common types of fungal growth on wood: (a) mold discoloration; (b) brown rotted pine (note the dark color and cubical checking in the wood); (c) white rot in maple (note the bleached appearance); (d) soft-rotted preservative-treated pine utility pole (note the shallow depth of decay)

With white-rot fungi, both the lignin and cellulose are usually removed, so the wood may lose color and appear whiter than normal. It does not crack across the grain, and until severely degraded, it retains its outward dimensions, does not shrink or collapse, and often feels spongy.

When combating fungi, the temperature and moisture content of the wood are essential to consider.

Most fungal decay can progress rapidly at temperatures that favor the growth of plant life in general. For the most part, decay is relatively slow at temperatures below 50 degrees Fahrenheit and above 95 degrees Fahrenheit. Decay essentially ceases below 35 degrees Fahrenheit or above 100 degrees Fahrenheit.

Serious decay also only occurs when the moisture content of the wood is above the fiber saturation point (about 30 percent). Fully air-dried wood usually will have a moisture content not exceeding 20 percent, and should provide a reasonable margin of safety against fungal damage.

Brown, crumbly rot, is sometimes called dry rot, but the term is incorrect because wood must be damp to decay, but may become dry later. There are also a few dry-rot fungi that have water-conducting strands; such fungi are capable of carrying water (usually from the soil) into buildings or lumber piles.


The decay cycle (top to bottom). Thousands of spores produced in a fungal fruiting body are distributed by wind or insects. On contacting moist, susceptible wood, spores germinate and create new infections in the wood cells. In time, serious decay develops that may be accompanied by formation of new fruiting bodies.

The early stages of decay are often accompanied by a discoloration of the wood, which can be difficult to recognize but is more evident on freshly exposed surfaces of unseasoned wood than on dry wood. Abnormal mottling of the wood color, with either unnatural brown or bleached areas, is often evidence of decay infection.

Late stages of decay are easily recognized, because the wood has undergone definite changes in color and properties. The character of these changes depends on the organism and the substance it removes.

If you see these tell-tale signs of decay on your wooden structures, and cannot dry the wood or turn down the temperature, researchers at the Forest Products Laboratory (FPL) offer these tips for cleaning outdoor surfaces prone to fungi, like your deck or siding. Fungus will always be among us, but detecting it, managing it, and mitigating its damage is well within our control.

For more information, please see Chapter 14 of FPL’s Wood Handbook: Wood as an Engineering Material

Curious Collection: Thousands of Decay Fungi Cataloged at FPL

The Forest Products Laboratory’s (FPL) Center for Mycology Research is home to one of the largest collections of wood-decay fungi in the world. The collection consists of an herbarium and a culture collection.

Photo courtesy of

Photo courtesy of

The herbarium serves as a national repository for wood-decay fungi collected by mycologists since the early 1900s. The fungi fruiting bodies (mainly conks, mushrooms, crusts, or stromata) are collected in the field and then dried and briefly frozen for insect control.

The culture collection is one of the largest assemblages of fungi in the world, containing about 12,000 isolates representing about 1,500 species. The collection is diverse, but primarily consists of Basidiomycetous fungi. Mycologists continuously collect new cultures of wood-decay fungi as they conduct research on fungal biodiversity throughout the world. These fungi are brought back to FPL and identified by experts, and cultures of the freshly collected fruiting bodies are made from spores, fungal tissue, or both.

The herbarium and culture collection are a valuable resource to the scientific community. Aside from contributing to further study of fungi through classification or DNA sequencing, the collection is also used in biotech applications. Examples of such work include using decay fungi to break down wood for pulp and paper or biofuels production, and for bioremediation of toxic pollutants in soil.

Wood decay fungi are also a potential source of pharmaceuticals, including cancer-fighting agents. Pharmaceutical companies have screened some of FPL’s fungi for their ability to produce chemicals that may be of use in medicine or other processes. Many opportunities exist for further work in this area.

Genetics Provide Valuable Insight into Mysterious Decay Fungi

Valuable insights to developing effective biological control agents for protecting conifer trees from root rot have been discovered.

Pine log extensively colonized by Phlebiopsis gigantea showing fruiting structures from which spores are released. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

Pine log extensively colonized by Phlebiopsis gigantea showing fruiting structures from which spores are released. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

An international team of 41 scientists from eight countries, including USDA Forest Service Forest Products Laboratory (FPL) researcher Daniel Cullen, unraveled the longstanding mystery as to how the Phlebiopsis gigantea fungus rapidly colonizes wood to the exclusion of other invading microbes.

Daniel Cullen, FPL research microbiologist

Daniel Cullen, FPL research microbiologist

The devastating conifer pathogens in the Heterobasidion genus cause substantial economic damage to conifer roots in the Northern Hemisphere, by infecting stumps and wounded trees.  Another common and benign fungus, Phlebiopsis gigantea, is able to rapidly colonize conifer wood and prevent Heterobasidion species and other pathogens from taking hold.

Recently reported in the prestigious open access journal PLOS Genetics, “These findings pave the way for our deeper understanding of the complex and multifaceted biochemical pathways by which wood-degrading fungi metabolize wood and its constituents,” according to Professor Robert Blanchette of the University of Minnesota.

The unusual ability of Phlebiopsis gigantea to rapidly colonize freshly cut conifers has been known for decades. How the fungus tolerates and degrades the resins that conifer trees use as part of their defense against all invading microbes was poorly understood until now. By identifying the key Phlebiopsis gigantea genes and enzymes involved in resin metabolism, more effective biocontrol strains can be developed. This knowledge will also be valuable in advancing the industrial bioconversion of woody biomass into useful products, including bioenergy-related products.

Scanning electron micrograph of a radial section of pine wood with Phlebiopsis gigantea filaments visible during attack. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

Scanning electron micrograph of a radial section of pine wood with Phlebiopsis gigantea filaments visible during attack. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

FPL assistant director Ted Wegner observed that “This important body of research provides a fundamental science base for developing commercially viable and environmentally preferable ways of protecting conifers from root rot as well as opening the door for new commercially viable and environmentally preferable forest biomass conversion technologies.”

Within its genome of 30 million base pairs, Phlebiopsis gigantea was predicted to harbor 12,000 protein-encoding genes. The team of researchers identified specific genes involved in the degradation of pitch and novel enzymes produced by Phlebiopsis gigantea that could be of value in the industrial bioconversion of woody biomass. For example, utilization of freshly harvested conifer wood for bioconversion or for paper manufacture can be complicated by the resinous materials. The enzymes and enzymatic processes employed by Phlebiopsis gigantea may lead to the development of new approaches for the reduction or elimination of troublesome resins that interfere with pulping and papermaking processes and products. According to Cullen, “While commercial applications may be years away, the research findings offer considerable promise in reducing the costs of pitch deposits in paper manufacture.”

Regarding the economic importance of controlling Heterobasidion root disease, Professor Sarah Covert of the University of Georgia stated that “Heterobasidion root disease is one of the most costly conifer diseases in the entire Northern Hemisphere.”

The complete report can be found at