Brown mould, white mould and grey mould
Refers to various forms of decomposition caused by wood-degrading fungi. The 3 main components of wood are cellulose, lignin and hemicellulose. Cellulose, which is made up of long twisted fibres, has the function of creating breaking strength in wood. In much the same way as concrete is given tensile strength by embedding an iron mesh (riven mesh). When the wood-degrading fungus breaks down the cellulose fibres, the breaking strength is removed and this degradation is called brown mould. With brown mould, the wood turns brown and cracks into blocks along and across the grain (fibre direction). House fungus, yellow dry rot, white dry rot, cork fungus and fan fungus are examples of brown mould-forming fungi.
Lignin, on the other hand, is the wood's "filler" - like the cement in a concrete mould. If the wood-degrading fungus breaks down the lignin in the wood, the cellulose strands will be left behind as distinct strands. This degradation is called white mould. With white mould, the wood is stringy and soft and does not crack. Coniferous wood does not change colour, darker hardwoods become bleached. White mould fungi include bark fungi and fireblight fungi.
With grey mould (surface rot), the wood turns grey and loses weight but retains its shape. Wet wood can be compressed, but regains its shape when the pressure is released. Small cracked blocks are formed when the wood dries out. Grey mould is caused by special fungi that form tunnels inside the cell walls of the wood as they decompose.
Fungi at a glance
| Fungi | Fruiting bodies | Surface mycelium | Decomposition |
|---|---|---|---|
| Dry rot fungus | Sticks out like consoles or is pizza-like. Folded orange-brown surface, rim thickened and white. | Young: Snow-white cottony, with water droplets Elderly: Greasy loose with strands, comes off in flakes, lemon-yellow spots, strands snap. |
Brun mulch. Crushed blocks in lengths from 5-10 cm. The wood is coloured brown. |
| Wet rot fungus | Fruiting bodies are infrequently seen. They are small and flat, 50-200 mm in diameter. Warty brown surface, margin flat and white. | Light brown to very dark brown, fixed and snake-like strands. | Brown rot. From small (rot damage) up to approx. 40-50 mm splitting blocks, the wood delaminates in the annual rings (fungal damage). Intact wood surface. |
| Mine fungus | White to light brownish, chalky and rub-off, firmly attached, small pores (large variation) | Young: Snow white, cottony. Older: Tough white pliant and cotton-like, mycelium possibly staining. |
Brown cuboidal rot. Small to very large crack blocks. Easily confused with True Dry Rot. |
| Serried crust fungus | In the dark: cauliflower-like, often with reddish spots. In light: like white bracket fungi growing in rows one above the other |
Sparse, but white coatings on fracture surfaces of rock chippings. Possibly dense and woolly. | Brown soil. 5-20 mm cracking blocks. |
| Tapinella | Yellow/brown toadstool with a suede-like surface, decurrent gills and a lateral stem. | Whitish to curry-yellow cobweb-like mycelium. Hair-fine whitish to curry-yellow strands/hyphae. | Brown mould. 5-50 mm rubble. Wood dark brown coloured. |
| Contiguous aspen bracket fungus | Brown, 10-20 mm thick, flat, pressed, tough with irregular dense pores | Yellowish cottony tufts in the frayed decayed wood. Fibres partially coated with brown deposit. | White rot. The wood fibres unfurl. |
| Gilled polypore | In bright, tough, corky shelves on the tree. Light brown pores underneath, the upperside brown and bristly, in dark, sterile brown pores. | In darkness: Sticking, white, fan-shaped - brownish, cork-like, indistinct, sticking threads. In light: Small whitish tufts between split blocks. |
Brown rot. The tree's annual rings are peeling open. Often small (2-20 mm) cracking blocks on the peeling areas. |
| Bark fungus | Flat, a few mm high, waxy/candle wax coating. | Very big variation. | White rot. The wood fibres unfurl. |