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Dry rot is wood decay caused by one of several species of fungi that digest parts of wood which give it strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resulted in a darkly colored deteriorated and cracked condition.
The life-cycle of dry rot can be broken down into four main stages. Dry rot begins as a microscopic spore which, in high enough concentrations, can resemble a fine orange dust. If the spores are subjected to sufficient moisture, they will germinate and begin to grow fine white strands known as hyphae. As the hyphae grow they will eventually form a large mass known as mycelium. The final stage is a fruiting body which pumps new spores out into the surrounding air.
In other fields, the term has been applied to the decay of crop plants by fungi. In health and safety, the term is used to describe the deterioration of rubber, for example the cracking of rubber hoses. [1]
Dry rot is the term given to brown rot decay caused by certain fungi that deteriorate timber in buildings and other wooden construction without an apparent source of moisture. The term is a misnomer [2] because all wood decaying fungi need a minimum amount of moisture before decay begins. [3] The decayed wood takes on a dark or browner crumbly appearance, with cubical like cracking or checking, that becomes brittle and can eventually crush the wood into powder. Chemically, wood attacked by dry rot fungi is decayed by the same process as other brown rot fungi. An outbreak of dry rot within a building can be an extremely serious infestation that is hard to eradicate, requiring drastic remedies to correct. Significant decay can cause instability and cause the structure to collapse.
The term dry rot, or true dry rot, refers to the decay of timbers from only certain species of fungi that are thought to provide their own source of moisture and nutrients to cause decay in otherwise relatively dry timber. However, there has been no published experimental evidence to support the phenomenon. [4] In modern texts, the term 'dry rot' is used in reference to damage inflicted by either: Serpula lacrymans (formerly Merulius lacrymans) predominantly in the United Kingdom and northern Europe; and/or Meruliporia incrassata (which has a number of synonyms, including Poria incrassata and Serpula incrassata) in North America. Both species of fungi cause brown rot decay, preferentially removing cellulose and hemicellulose from the timber, leaving a brittle matrix of modified lignin.
The term dry rot is somewhat misleading, as both species of fungi Serpula lacrymans and Meruliporia incrassata require an elevated moisture content to initiate an attack on timber (28–30%). Once established, the fungi can remain active in timber with a moisture content of more than 20%. At relative humidities below 86 percent, growth of Serpula lacrymans is inhibited, but it can stay dormant at relative humidities down to 76 percent. [5] These relative humidities correspond to equilibrium moisture contents of wood of 19 and 15 percent, respectively. It is to be remembered that most forms of rot cannot be stopped.[ citation needed ]
An explanation of the term "dry rot" circles around boatyards periodically. In the age of wooden ships, boats were sometimes hauled for the winter and placed in sheds or dry dock for repair. The boats already had some amount of rot occurring in the wood members, but the wood cellular structure was full of water making it still function structurally. As the wood dried out, the cell walls would crumble. In other words, the wood was already rotten and as the boat dried, the wood collapsed and crumbled, causing the workers in the yard to determine it was "dry rot", when in fact, the wood had been rotten all along.
Schilling & Jellison [6] note the potential efficiency of these 'dry rot' fungi in growing away from direct moisture sources, although there is no reference for how efficient a brown rot fungus has to be at translocating water in order to be classed as 'dry rot'. Some have suggested the importance of these fungi providing their own source of nutrients as being more significant than providing an adequate source of moisture. Schilling [7] suggests efficient nutrient translocation and utilization, notably nitrogen and iron, may be more distinctive in these species than water translocation. Water translocated in this fashion carries nutrients to the extremities of the organism; not, as is sometimes inferred, to simply render dry timber wet enough to attack. Coggins [8] goes into more detail about water movement in Serpula lacrymans.
The perpetual saturation of wood with water also inhibits dry rot, as does perpetual dryness. [9]
Dry rot would appear to be a paradoxical term seemingly indicating decay of a substance by a fungus without the presence of water. However, its historical usage dates back to the distinction between decay of cured wood in construction, i.e. dry wood, versus decay of wood in living or newly felled trees, i.e. wet wood. [10]
'Dry rot' is an 18th-century term that generally described what is now called brown rot. The term was used because the damage was present in cured or dried timber of ships and buildings and was thought to be caused by internal ‘fermentations’ rather than water. This contributes to the etymological fallacy that dry rot requires less or no water than other species that use the brown rot decay mechanism.
The (London) Times on Tuesday 12 March 1793 carried an advertisement that informs the reader that the "British Colour Company, No. 32, Walbrook, London continues to use, manufacture and sell paints prepared with the Oil of Coal, which is of a very penetrating nature, and hardens wood in an uncommon degree protecting it from weather, dry rot and ice". [11]
In the early 19th century the rapid increase in instances of timber decay attributed to dry rot (brown rot) in the British naval fleet brought the term into wider usage. Thomas Wade's 'A Treatise on the Dry Rot in Timber' was published posthumously by the Navy Office in 1815 following his investigation of the matter in ships from various countries. [12] The second HMS Queen Charlotte was launched in 1810 and, when inspected, the timbers of the upper decks were found to be infected with 'the dry rot'. By 1816 the cost of repairs for this vessel had exceeded the ship's original construction cost. [13]
Texts published in the 19th and early 20th centuries also used the term to describe fungi which produced substantial (white-colored) mycelium, including Antrodia (Fibroporia) vaillantii .
Eventually, the term dry rot came to apply to only one or two fungi[ citation needed ] the main one being Serpula lacrymans , in the majority of texts dealing with the subject, predominantly from the United Kingdom. This type of fungal decay subsequently also became known as 'true dry rot'. It has even been proposed to use the term water-conducting fungi in the category of brown rot rather than dry rot. [14] However, although the fungi such as these can transport water, it is disputed [4] that it can use this water to increase the moisture content of otherwise dry wood. Whilst it may be disputed as the citation notes, the epithet 'lacrymans' is derived from the Latin word 'lacrimare', meaning 'to weep' and most surveyors of rotted buildings have noted the tear drops formed by the fungus as water forms on the hyphae. These water droplets are photographed in Rentokil's book "Decay of Timber in Buildings" Figure 24. [15] There is, however, no evidence these small amounts of water on the hyphae cause a significant increase in the moisture content of otherwise dry wood.
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Dry rot can be very difficult to remediate unless the timber is dried. In some cases after this is done, decayed areas can be treated with special epoxy formulations that fill-in the channels of the damaged wood, killing the rot and improving structural integrity. However, this type of treatment can actually promote decay [16] in wood in exterior service unless the epoxy application is designed to shed water. [17] Epoxy or other polymers will trap moisture behind the patch, causing more decay in the surrounding previously uninfected zones unless the repaired zone is protected from recurring water events. Commercial ethylene glycol (commonly sold as antifreeze) and many other toxic diffusible compounds can diffuse into the wood to kill the fungus, but they also can diffuse out of wood that is repeatedly wetted. Diffusion of these toxic compounds out of the wood, and into surrounding soils and plants is not appropriate from a toxicity or environmental standpoint, [18] and these types of treatment are not recommended for wood in-service. Certain copper compounds, such as copper naphthenate, are available as a brushable solution and are frequently used when dry-rot damage is repaired by splicing in new wood; after removal of bulk rotten wood the remaining original surface is saturated with such a compound (typically green in color) before application of the new wood.
In certain buildings, particularly those with solid 9 inch (or greater) brickwork and those built using lime mortar and flintstone, dry rot has been known to travel through and along the wall surface behind plaster and render. It is therefore recommended, by companies that sell this service, that where dry rot is found, plaster and wall coverings should be stripped back to a metre past the infestation in all directions and the whole area treated. However, given that dry rot attacks only wet timber, common sense should dictate that plaster need not be removed where there is no timber or any timber is dry (outside the zone of wetting that caused the outbreak)[ citation needed ]. Identifying the source of water and allowing the affected timbers to dry will kill dry rot, as it is a fungus and requires water as all fungi do. This will not, however, kill any spores left behind, which will remain viable and cause the rot to return upon wetting[ citation needed ].
A mold or mould is one of the structures that certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not all fungi form molds. Some fungi form mushrooms; others grow as single cells and are called microfungi.
In trees, heart rot is a fungal disease that causes the decay of wood at the center of the trunk and branches. Fungi enter the tree through wounds in the bark and decay the heartwood. The diseased heartwood softens, making trees structurally weaker and prone to breakage. Heart rot is a major factor in the economics of logging and the natural growth dynamic of many older forests. Heart rot is prevalent throughout the world affecting all hardwood trees and can be very difficult to prevent. A good indication of heart rot is the presence of mushrooms or fungus conks on the tree.
Serpula lacrymans is one of the fungi that cause damage to timber referred to as dry rot. It is a basidiomycete in the order Boletales. It has the ability to rapidly colonise sites through unique and highly specialised mycelium which also leads to greater degradation rates of wood cellulose.
Monilinia fructicola is a species of fungus in the order Helotiales. A plant pathogen, it is the causal agent of brown rot of stone fruits.
A wood-decay or xylophagous fungus is any species of fungus that digests moist wood, causing it to rot. Some species of wood-decay fungi attack dead wood, such as brown rot, and some, such as Armillaria, are parasitic and colonize living trees. Excessive moisture above the fibre saturation point in wood is required for fungal colonization and proliferation. In nature, this process causes the breakdown of complex molecules and leads to the return of nutrients to the soil. Wood-decay fungi consume wood in various ways; for example, some attack the carbohydrates in wood, and some others decay lignin. The rate of decay of wooden materials in various climates can be estimated by empirical models.
Mycelial cords are linear aggregations of parallel-oriented hyphae. The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae. Cords may look similar to plant roots, and also frequently have similar functions; hence they are also called rhizomorphs. As well as growing underground or on the surface of trees and other plants, some fungi make mycelial cords which hang in the air from vegetation.
Thielaviopsis basicola is the plant-pathogen fungus responsible for black root rot disease. This particular disease has a large host range, affecting woody ornamentals, herbaceous ornamentals, agronomic crops, and even vegetable crops. Examples of susceptible hosts include petunia, pansy, poinsettia, tobacco, cotton, carrot, lettuce, tomato, and others. Symptoms of this disease resemble nutrient deficiency but are truly a result of the decaying root systems of plants. Common symptoms include chlorotic lower foliage, yellowing of plant, stunting or wilting, and black lesions along the roots. The lesions along the roots may appear red at first, getting darker and turning black as the disease progresses. Black root lesions that begin in the middle of a root can also spread further along the roots in either direction. Due to the nature of the pathogen, the disease can easily be identified by the black lesions along the roots, especially when compared to healthy roots. The black lesions that appear along the roots are a result of the formation of chlamydospores, resting spores of the fungus that contribute to its pathogenicity. The chlamydospores are a dark brown-black color and cause the "discoloration" of the roots when they are produced in large amounts.
Porodaedalea pini, commonly known as the pine conk, is a species of fungus in the family Hymenochaetaceae. It is a plant pathogen that causes tree disease commonly known as "red ring rot" or "white speck". This disease, extremely common in the conifers of North America, decays tree trunks, rendering them useless for lumber. It is a rot of the heartwood. Signs of the fungus include shelf-shaped conks protruding from the trunks of trees. Spores produced on these conks are blown by the wind and infect other trees. Formal management of this disease is limited, and the disease is controlled primarily by cultural practices. Red ring rot is an important forest disturbance agent and plays a key role in habitat formation for several forest animals.
Spalting is any form of wood coloration caused by fungi. Although primarily found in dead trees, spalting can also occur in living trees under stress. Although spalting can cause weight loss and strength loss in the wood, the unique coloration and patterns of spalted wood are sought by woodworkers.
Crucibulum is a genus in the Nidulariaceae, a family of fungi whose fruiting bodies resemble tiny egg-filled bird's nests. Often called "splash cups", the fruiting bodies are adapted for spore dispersal by using the kinetic energy of falling drops of rain. The "eggs" inside the bird's nests are hard waxy shells containing spores, and tend to stick to whatever nearby herbage they land on, thus increasing the odds of being consumed and dispersed by herbivorous animals. Members of this genus are saprobic, obtaining nutrients from dead organic matter, and are typically found growing on decayed wood and wood debris. The three known Crucibulum species are distinguished from other genera of the Nidulariaceae by their relatively simple funiculus – a cord of hyphae that connects the peridiole to the exterior of the bird's nest.
Panellus stipticus, commonly known as the bitter oyster, the astringent panus, the luminescent panellus, or the stiptic fungus, is a species of fungus. It belongs in the family Mycenaceae, and the type species of the genus Panellus. A common and widely distributed species, it is found in Asia, Australia, Europe, and North America, where it grows in groups or dense overlapping clusters on the logs, stumps, and trunks of deciduous trees, especially beech, oak, and birch. During the development of the fruit bodies, the mushrooms start out as tiny white knobs, which, over a period of one to three months, develop into fan- or kidney-shaped caps that measure up to 3 cm (1.2 in) broad. The caps are orange-yellow to brownish, and attached to the decaying wood by short stubby stalks that are connected off-center or on the side of the caps. The fungus was given its current scientific name in 1879, but has been known by many names since French mycologist Jean Bulliard first described it as Agaricus stypticus in 1783. Molecular phylogenetic analysis revealed P. stipticus to have a close genetic relationship with members of the genus Mycena.
Dry rot treatment refers to techniques used to eliminate dry rot fungus and alleviate the damage done by the fungus to human-built wooden structures.
Fomes fomentarius is a species of fungal plant pathogen found in Europe, Asia, Africa and North America. The species produces very large polypore fruit bodies which are shaped like a horse's hoof and vary in colour from a silvery grey to almost black, though they are normally brown. It grows on the side of various species of tree, which it infects through broken bark, causing rot. The species typically continues to live on trees long after they have died, changing from a parasite to a decomposer.
Serpula is a genus of fungi in the family Serpulaceae.
Peniophora quercina is a species of wood-decay fungus in the family Peniophoraceae. It produces fruit bodies that vary in appearance depending on whether they are wet or dry. The wet fruit bodies are waxy and lilac, and attached strongly to the wood on which they grow. When dry, the edges curl up and reveal the dark underside, while the surface becomes crusty and pink. P. quercina is the type species of the genus Peniophora, with the species being reclassified as a member of the genus upon the latter's creation by Mordecai Cubitt Cooke. P. quercina is found primarily in Europe, where it can be encountered all year. Though primarily growing upon dead wood, especially oak, it is also capable of growing upon still-living wood.
Xylobolus frustulatus, commonly known as the ceramic fungus or ceramic parchment, is an inedible species of crust fungus in the Stereaceae family. The fruit body forms small, hard, flat crust-like aggregations that resemble broken pieces of ceramic tile. These pieces are initially whitish before turning yellow-brown to gray-brown in age. The spore-bearing cells cover the upper surfaces of the fruit body. A saprobic species, it grows on well-decayed oak wood in Asia, northern Europe, and North America.
Serpula himantioides is a species of fungus that causes damage to timber referred to as dry rot. It is a basidiomycete in the order Boletales. It has been found on all continents except for Antarctica. Recent molecular work demonstrates that S. himantioides is a species complex including multiple cryptic lineages.
Aspen trunk rot is a fungal disease that causes stem decay heart rot of living aspen trees. The pathogen that causes this disease is the fungus Phellinus tremulae. Most of the symptoms of this disease are internal, with the only external signs of a diseased aspen being fruiting bodies called conks. A single conk found on an aspen can indicate advanced decay of up to 82% of the tree volume. Internal decayed wood of freshly cut aspens is spongy, yellow/white colored, surrounded by black zones of discoloration, and contains a distinct wintergreen smell. The fungus is spread via airborne spores released from the fruiting body which can infect through dead branches, branch stubs, or wounds in the tree. Although no direct management control is known, harvesting aspen stands that have been damaged or harvesting stands before decay becomes advanced minimizes tree loss. Aspen wood is white, malleable but strong, and heat-tolerant and therefore has many commercial uses including matches, packing paper, lumber, plywood, pulp, and animal beds. Aspen trees diseased with aspen trunk rot decrease the economic value of the lumber.
Phlebia radiata, commonly known as the wrinkled crust, is a common species of crust fungus in the family Meruliaceae. It is widespread in the Northern Hemisphere. It grows as a wrinkled, orange to pinkish waxy crust on the decaying wood of coniferous and deciduous trees, in which it causes a white rot. The fungus was first described scientifically in 1821 by Elias Magnus Fries.
Sistotrema brinkmannii, a resupinate wood-rotting basidiomycete, is a fungus found in soil, moss, debris, rotten woods as well as woods including seedling roots of Pinus banksiana Lamb. and ectomycorrhizae. No health issues caused by this fungus in human and animals have been reported although it is causative of brown rot. This fungus grows rapidly on malt extract agar (MEA), forming white mats with a faint sweet odour. It is commonly called "chain chlamydospore fungus" because bulbils are formed by chains of its cells that resemble chlamydospores. The basidia of this fungus are urniform and usually possess 6-8 sterigmata, and the spores are smooth and slightly curved.