Premature decay by white rot organisms


Reports of early failure in water reed thatch, within 4-10 years, were first recorded in 1970, and by 1983 had given rise to considerable cause for concern. At that time the majority of affected reed was home produced; researchers from the Universities of Bath and East Anglia investigated both the potential for infection of freshly harvested reed during storage and also studied the degradation process within thatch. Then as now complaints are associated with soft, weak reed, colonisation of the surface by clumps of organisms that dry out in sunny conditions and cause the surface to physically degrade in windy conditions. This surface colonisation and physical Prolonged periods of rain encourage the colonisation of the straw thatch surface with algae and mosses. These hold moisture and prevent the thatch from drying out interaction with the thatch allows the ingress of water into underlying thatch layers providing conditions suitable for further degradation of the reed by fungi and a subsequent reduced life expectancy for the roof. The main body of research on decay of lignin rich materials has been carried out on wood and wood products. However, there are only a limited number of organisms that form symbiotic functions in the decay process many of these organisms appear to naturally colonise both wood and other decaying vegetation such as thatch. In this particular form of attack, decay is not homogenous across the whole surface of the coat work, but can be seen as “bleached” areas in either zones or patches; this type of decay is not necessarily associated with high wear areas of a roof such as the junctions of dormers, valleys or gullies. Stems taken from within these patches have often lost both tensile and compression strength causing them to collapse and fragment.
Scanning electron micrograph of basidiomycete “gill structures” hanging from a length of reed in an advanced state of decay. The gills hang vertically from the underside of the straw and produce large numbers of spores. Most have been shed from these gills, leaving “pimples” where they grew.

Scanning electron micrograph of basidiomycete “gill structures” hanging from a length of reed in an advanced state of decay. The gills hang vertically from the underside of the straw and produce large numbers of spores. Most have been shed from these gills, leaving “pimples” where they grew.

 

In nature, old plant material is composed of tough woody tissue, lignin with a small level of carbohydrate present to initiate the process. Many authors on the subject describe a cycle initiated and maintained by groups of organisms each with a specific role at different stages of the decay cycle. In natural reed beds, organisms capable of degrading lignin and cell walls only colonise dead tissue and since the process starts at ground level it is not until the toughest part of the plant (the butt end) has died that breakdown takes place. Under natural conditions the stem then breaks and falls leaving a short stump above the living rhizome, fallen reeds then decompose as part of the natural cycle of the reed bed. The process is complex but the physical manifestation of the decay process on a small number of thatched roofs in different geographical locations all have common features in the manifestation and progression of the break down process.
When early decay in water reed thatch was first identified it was realised that a change in management and cleanup of reed beds was essential to ensure the survival of the area, in addition to quality control of water reed as a thatching raw material. The efficient management of the Broads ecosystem probably account for the absent of problems with homegrown water reed at the present time.