Investigating CLT’s Ability to Fight Fungus

The growing reputation of cross-laminated timber (CLT) as a sustainable, cost-effective, and innovative building material has prompted researchers at the Forest Products Laboratory (FPL) to build upon past research and investigate the material’s ability to fight against fungus.

Intact cross-laminated timber panel section (left); 4-in. cube cut from panel section for scaled-up decay testing.

(A) Intact cross-laminated timber panel section; (B) 4-in. cube cut from panel section for scaled-up decay testing.

Praised for its many benefits, including speed of construction, cost, sustainability, excellent thermal and sound insulation, and fire restriction qualities, the pre-fabricated building material has made a name for itself in the construction and worldwide mass timber market. CLT has already made an appearance in a variety of high-rise apartment buildings in the Pacific Northwest and Southeast United States, urging scientists in the Lab’s Durability and Wood Protection Unit to further examine how the timber fairs against a rainy, humid climate.

The study builds upon past conclusions that untreated CLT is susceptible to mold and a variety of fungi. While decay can be reduced with preservatives such as boron, researchers are using more methods to investigate resistance treatments.

Scientists have implemented soil block assay tests on numerous random samples of CLT, and also plan to conduct mass loss and x-ray density profiling to assess decay in CLT.It is hoped that this exploration will help researchers develop more targeted fungal reduction methods for CLT.

The project will conclude in early 2017.  For more information on CLT and fungal resistance, read the full Research in Progress report.

Blog post by Francesca Yracheta

Fungi Friday : Shiitake Science Paved Path For Future Fungi

The following is adapted from Forest Products Laboratory 1910 – 2010 : Celebrating a Century of Accomplishments.

In the late 1970s, Forest Products Laboratory researcher, Gary Leatham, completed a doctoral thesis based on his research on growth of the Japanese Islands variety of Shiitake. Continuing his research at FPL, in 1982 he published “Cultivation of shiitake, the Japanese forest mushroom, on logs: a potential industry for the United States.”


Shiitake mushrooms, growing on sawdust rather than on logs. This research led to the creation of an alternative method of commercially growing these mushrooms.

This paper and a number of public seminars stirred a lot of interest and helped make commercial cultivation possible in the United States. It was also discovered that the edible Shiitake mushrooms (Lentinus edodes) grow faster on shredded oak residue than on logs.


Chittra Mishra, a research associate from the National Chemistry Laboratory in Poona, India, researching solidwood bioconversion using shiitake mushrooms.

This finding was a spin-off of long-term basic research toward selective degradation of lignin for biopulping. By producing Shiitake, low-quality hardwoods can be converted directly to a high-value food.

Shiitake growing has since become a budding industry in the United States, creating jobs and utilizing wood that would otherwise be wasted.

Scientists Receive Grant Funding for White-Nose Syndrome Research

Four USDA Forest Service research studies examining strategies for managing white-nose syndrome (WNS), a fungal disease that has killed an estimated 5 to 6 million bats in the United States, are among projects that will receive grant funding from the U.S. Fish and Wildlife Service.

“Fungi and bats are among the most elusive species on the planet, which makes white-nose syndrome a particularly challenging disease to manage,” said Michael T. Rains, Director of the Forest Service’s Northern Research Station and the Forest Products Laboratory. “Forest Service scientists have expertise on both and are working on a variety of approaches to reduce the mortality of bats in the face of this devastating disease. We are honored and grateful for the U.S. Fish and Wildlife Service’s support of this research.”

Little brown bats hibernate together in caves. Most of these bats have fungal growth on their noses. Photo courtesy of Nancy Heaslip, NY Department of Environmental Conservation.

Little brown bats hibernate together in caves. Most of these bats have fungal growth on their noses. Photo courtesy of Nancy Heaslip, NY Department of Environmental Conservation.

White-nose syndrome is caused by a cold-loving fungus, Pseudogymnoascus destructans (Pd), which is deadly to hibernating bats because it penetrates tissues of the nose and mouth as well as the wings, which are vital to bats’ ability to avoid dehydration and maintain body temperature. In affected hibernacula, 78 to 100 percent of bat populations have died.

As a major predator of defoliating forest and agricultural insects, bats are important to forests and forest health. The value of bats to the agricultural industry is estimated at $23 billion/year.

The grants, which were announced Tuesday, include a total of $410,690 for Forest Service research at the Northern Research Station, the Southern Research Station, and the Center for Forest Mycology Research, part of the Forest Products Laboratory. Projects include:

  • In Columbia, Mo., Sybill Amelon is leading a project that includes Forest Service scientist Dan Lindner, Chris Cornelison, a postdoctoral research associate at Georgia State University, and Sarah Hooper, a comparative medicine resident at the University of Missouri, to explore the use of a native soil bacterium to produce natural volatiles that inhibit growth of the Pd fungus that causes WNS. Their work received a grant of $165,000.
  • In Madison, Wis., Lindner and a team that includes Forest Service researchers Jessie Glaeser, Jonathan Palmer and Michelle Jusino are analyzing the sensitivities of Pd to UV light and the possibility of using light to kill Pd in caves bats use to hibernate. Their work received a grant of $129,681.
  • In Clemson, S.C., Susan Loeb is working with Eric Britzke of the U.S. Army Corps of Engineers Engineer Research and Development Center on research that focuses on understanding the vulnerability of tri-colored bats to WNS in the southern United States. Loeb’s work received a grant of $95,409
  • In Madison, Glaeser is developing decontamination protocols to mitigate human-based transmission of Pd. She will receive a grant of $20,600.

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

Visiting Scientist Contributes to Fungal Database

Collaboration brings a wealth of resources to research, and international visiting scientists can often be found working along side permanent researchers at the Forest Products Laboratory (FPL).

Dr. Xingxia Ma, Chinese Academy of Forestry

Dr. Xingxia Ma, Chinese Academy of Forestry

One such scientist is Professor Xingxia Ma, Chinese Academy of Forestry, Bejing, China, who recently completed a research sabbatical in the Durability and Wood Protection research unit at FPL.

Dr. Ma’s research included developing comparative decay test methodologies and genetic identification of soil-inhabiting fungi present in laboratory fungal cellar beds.

Fungal cellar beds are a standardized method for accelerated testing of wood and wood-based materials in contact with soil.The soil bed is amended with select fungi that cause brown- and white-rot decay of wood. These fungi are intended to accelerate the rate of decay in wood samples that are embedded in soil tubs; however, the majority of decay observed in soil bed tests is usually a third type of decay called soft-rot. Fungi that cause soft-rot thrive in environments with elevated moisture and high nitrogen content.

Fungal cellar isolates were Sanger-sequenced for genetic identification and entered into FPL’s fungal database. Development of a fungal database was identified as a National priority by members of the wood protection industry.