Biodeterioration Diagnostics Database

  I.  Title: Brown rot decay of cedar wood on exterior decking

 II.  Deterioration Agent: A brown rot fungi

III. Location: Minneapolis, MN, USA

 IV. Description of Problem: Brown Rot

This house was constructed in 1856 and resides near the University of Minnesota. It served as the home for the University of Minnesota’s first president and is one of the oldest homes in Minneapolis. It is now home to the Minnesota Alpha chapter of Sigma Phi Epsilon Fraternity. The house joined the Minneapolis Heritage Preservation Commission in 1976. It suffered a devastating fire in 1992 and portions of the house were rebuilt shortly after. There are multiple areas around the exterior (mainly the front and back porch) that suffer from brown rot decay. The re-construction of the front and back porch could have led to and or aided in the problems described below. The carpenters may have not used properly treated wood, they may have not dip-treated the ends of the boards if they had been cut to size, they used iron nails which could have been a point of entry for the fungus, and may have not taken ground moisture or rain drainage into consideration. The main area of rot occurs at the junction between the porch and a custom made pillar. Due to the custom woodwork, it is possible that the carpenters did not properly treat/close all seams and edges. There are no sporophores present but the brown rot can be identified by the presence of cubical checking, the deep brown color from the remaining lignin, and the ability to crush the wood in between fingers which forms a powder. There is also galvanic corrosion present on all of the nails. The Fenton reaction between the fungi and wood causes an early and rapid strength loss by hydrolyzing cellulose and hemicelluloses.  The rapid strength loss of the porch proves to be dangerous for anyone walking on its surface. Due to this fact, the structural boards, the decking boards, and the custom pillar need to be replaced. The Heritage Preservation Commission requires that the façade stay identical to the original design. This makes replacing these exterior structures more difficult due to the cost and expertise required to meet the Commission’s standards.

The biodegradation problem that will be focused upon is large woodpecker holes.   Picture 1 demonstrates the general shape and size of the holes.   The holes generally have diameters between one and two inches.   There are at least 10 holes that are of this general size and shape, but due to this house being recently purchased, more holes may exist that are covered up or that have been repaired.  From picture 2 the distribution and extent of the holes can be clearly noticed.  The holes are all located in the cedar siding of the house about 10 to 20 feet from the ground on all sides of the house.  These holes are believed to be for the purpose of nesting due to the size.  If the woodpeckers were interested in finding insects within the wood or were making noises to attract mates then the holes would be smaller in diameter. 

Picture 1

These holes are problematic in more ways than just those that meet the eye.  What does meet the eye is that visually these holes are quite noticeable when walking around the home and when driving on the street, which is thirty feet away.  Having holes of this size does damage the aesthetics of the house, but large holes in the siding also allow for future biodegradation problems.  The holes are a prime location for moisture to get behind the wood or be absorbed.  The presence of moisture is a catalyst of major biodegradation problems including insects, fungi, and bacteria infestation.  The first and foremost concern to the occupants of the house is that the noise caused by the creation of these holes is an audio irritation.  When the holes are made in certain locations on the house the acoustics of the house’s construction seem to amplify the sound within the house.  The audio problem persists as long as the woodpeckers inhabit the holes because they continue to peck at the siding. 

Picture 2

The damage and attack was first noticed when the sound of tapping was noticed.  Once attention was drawn to the damaged area, the woodpeckers were visually observed.  The holes currently being constructed as well as those that had been filled in by the previous owner were then inspected.  From seeing the size of the holes and the bird creating the holes, it was logically induced that a downy woodpecker was indeed the cause the holes and that the holes were meant as a place of habitation.  Visually the woodpecker was identified as being a downy woodpecker (Picoides villosus)2 by its white belly, red patched head, and black wings with white spots or stripes.  While having similar markings to Hairy Woodpeckers, its smaller stature, 6.5 to 7 inches long instead of 8.5 to 10, and shorter beak differentiate it.4

Carpenter ants (Camponotus spp.) were discovered in the walls of a suburban Minneapolis home. Ants were identified using the following characters: 1) individuals had a single node between thorax and abdomen, along with a narrow junction between abdomen and thorax, unlike termites, 2) there was an angular front top end to the abdomen (see picture), 3) there was a circle of hairs around the anus at the tip of the abdomen, 4) all individuals were black (unlike termites which have creamy white individuals, and 5) it was infesting this house in MN, clearly a pest but would have really been at the geographic range limit for a termite. This is likely Camponotus pennsylvanicus, being in mid-USA.

Once discovered, the damage was located as being in the insulation, although this was verified from the inside and no pictures are available from inside. Ants entered through an anchored portion of the window crank and could be followed in and out. In the cover of dark, the ants were followed streaming out of this nest, a secondary nest. Carpenter ants were foraging for sugar sources (they do not injest wood as a food source - this is why they can colonize insulation). We hoped to track them back to the primary nest, which can be done by following the ants after dusk. We did not succeed, however, so we could not treat the primary nest (likely in a rotting tree or tree with a rotten branch point).

While inspecting a very old garage that is beginning to lean to one side, a likely brown rot fungal infestation was observed. The garage is constructed of wood over a cement floor, however the wooden walls of the garage are in direct contact with soil. The garage was present when the associated house was purchased in 1979. It is unknown whether the wood used to build the garage has been treated, and if it has, what the chemical or dosage was for the treatment. Also pertinent, the garage is located underneath a pine tree. Pine needles have fallen on the roof and collected in piles on the roof that have been the site of their decay from needles into unidentifiable organic matter. These piles could be a source of moisture or fungal spores. The other potential source of fungal colonization could be the soil. The infestation was observed boards in the wall of the garage near the ground; it was also observed in wood trim along the edge of the roof. The full extent of fungal networks and growth is unknown, however there are several areas of concentrated symptoms, such as brown flaky wood with visible cubicle checking.

The use of low quality pine for treated wood products can yield poor results. You can't make a silk purse from a sow's ear!

Lots of juvenile wood in this piece renders it useless when it dries.

Addition completed in 2000, photo taken in 2009. Fungal decay (organism not id'ed) is extensive.

Sometimes treated and even untreated decking boards are used that contain varying degrees of juvenile wood.  Because juvenile wood shrinks longitudinally from 2-20x more than mature wood, decking boards with high-degrees of juvenile wood that are restrained by metal fasteners and that are regularly exposed to direct rainfall (wetting) followed by intense sunlight (drying) sometimes experience visual degradation of the top surface and later may eventually experience mechanical failure of the wood.

A)  Description of the cabinet condition and potential decay occurrences

Oak wood was used for the cabinet under the counter in basement bathroom.  As the cabinet was built by a professional wood furniture production company, I assume the wood was untreated before the coating was applied.  The cabinet was built in 1990 along with the house and the decay problem was found at very advanced stage by 2008.  Water marks together with a damaged coating were observed on the bottom corner of the right side of the cabinet and some black dots are spread on the surface of the cabinet along with the water mark (Figure 1a).  These were raised and looked like sclerotia or other fungal resting structures.  And under the microscope, when punctured, these released spores.

The possible occurrence of this situation is mainly due to the mop that used to be stored at the right side of this cabinet.  Not only because the moving of mop caused mechanical wears on the cabinet coating on the corner (Figure 1b), the mop also reduced the ventilation on this corner.  This together with the high moisture content observed in this bathroom (40-50% all year round), would explain how water got a chance to penetrate and accumulate within the cabinet wood.  Furthermore, heat outlets maintain a warm condition for living organism.  All these factors have provided the microorganisms a suitable living environment with suitable temperature and suitable moisture content.  When it comes to the food resource for these microorganisms, wood of the cabinet is a good choice.  Although oak wood is naturally resistant, over-exposing the wood in excessive water for a long period of time without coating would decrease the durability of this wood due to leaching, volatilization as well as oxidation of protection materials such as extractives and preservatives.

B)  Deterioration Agent Determination

In order to determine the microorganism that caused the decay, the deterioration agent was separated from cabinet surface and plated on agar.  After two weeks incubation at room temperature, the strains were examined under the microscope (Figure 2a).  A soil test of this organism is still in process. 

According to the observation, the agent of decay found most likely belongs to Aureobasidium Genus which is a type of saprophytic or weakly parasitic sapstain fungi, most probability Aureobasidium pullulans (1). The hyphae of this fungus are septate and not extensive. When the colonies are young, the mycelium is hyaline.  As they grow and mature rapidly, the hyphae become dark with age and showed a smooth black shiny appearance (Figure 2b).  Conidiogenous cells are not fully differentiated in these fungi, so no conidiophore is found under microscope.  By the side of the old mycelium lots of conidia are borne.  These conidia are subhyaline to dark, unicellular, oval shaped (Figure 2c).  Based on the field book, these conidia can produce other conidia and form secondary blastoconidia by budding from the old conidia (1).

C)  Possible Effect

This sapstain fungus will cause discoloration and maybe some disfigurement of the wood surface.  It is commonly believed that the sapstain fungi will not lead to a decrease in wood strength.  However, the result from our course projects shows that the wood infected by sapstain fungi is more susceptible to brown rot problems, which leads to server strength loss of the wood.  In this case, the counter which is supported by the cabinet is exposed to the risk of felling.  The other issue of this infection is that the sapstain fungi will increase the permeability and decrease the durability of this piece of wood which also deduce the quality of this cabinet. 

Softwood rounds used as a parking lot bumper near Jackson Hole, Wyoming showed signs of defibration on the upper surface. Salt defibration has been reported from Antarctica (Blanchette et al. Polar Rec 38:313–) as an unusual decay phenomenon, but here it is near 45 degrees latitude in the intermountain West of the Rocky Mountains. This defibration results in accumulation of wood fibers on the surface and exposes fresh wood to UV damage and more defibration. In this case, if there was any preservative treatment in the wood, this slow progressive decay could expose less resistant wood and hasten decay problems. The defibration may also be as a result of diffusible treatment chemicals. Although in historic objects and buildings this would be a worry, this process in low-value situations like this is mostly curious and perhaps useful to scientists interested in delignification processes. When I first looked at this 'fuzzy' surface and saw two furry mountain dogs playing around in the owner's cabin porch, I thought I was looking at dog fur, but you can see in the close-up photos that wood fibers are sloughing off. I would never have looked closer if I hadn't read about defibration in polar huts. This area in Wyoming receives 300+ inches (750+ centimeters) of snow annually, and this means the snow plow and the salt are nearly in constant action during the winter. This was on a gravel road portion, however, so it is unclear if salt would be used. Additionally, visitors using the parking lot probably stand on these horizontal rounds often (see the image of me performing my version of a three-point bending test). Salt or preservative chemicals (etc.) may help delignify the wood near the surface, a phenomenon that has been seen in Antarctica on explorer's huts exposed to salty air and wind, as well as in other sea-side areas I'm told . Here, this problem may be exacerbated in the high desert weather that can bake the surface. As in any situation, the size of the problem depends on the cost of the material replacement and the risk. Both are low here, so this is not a major financial loss or safety hazard. Instead, it is just a nice example of how learning about a problem common to one situation (windy polar buildings) can be useful for deducing similar problems occurring in new contexts (visitor-rich, landlocked Wyoming).

Untreated wood, most likely southern yellow pine, was used for steps leading up to the deck shown in the attached images. The steps were built in 1999 along with the house, and the decay problem was very advanced by 2004. The steps look like they were painted gray, but the paint has chipped and worn, exposing untreated wood. The deck itself was 0.25 pcf treated wood and, at the time of these photos, did not show signs of the fungus (sporophores, cubical checking, etc.). Clearly, the agent of decay is a fungus. The sporophore belongs to Gloeophyllum sepiarium, also known as the 'mazegill' fungus. You can see its sporophore as a rust-colored protrusion (a small shelf fungus) at the front end of the step. It is a brown rot, so the problem the landlord faces here is three-fold: 1) the steps need replacing, immediately, 2) the renters are at risk for falling through the deck because brown rot fungi reduce strength in wood quickly and 3) the mycelial mass of the fungus in this wood can act as a source for problems elsewhere, including the deck. Assuming CCA was the treatment for the deck boards (pre-2004), there should have been little leaching since being built and there is lower potential, but at 0.25 pcf, you could still have decay. Some brown rot fungi are more tolerant/resistant of heavy metals. Also, one of the images shows that the nail fasteners have failed, and they do not look galvanized, etc. There was likely galvanic corrosion and possibly iron leaching into the wood which, for iron-dependent brown rot fungi, may be a problem.