Decay Fungi on Trees

Every year winter gales highlight the need to ensure that trees are in a sound condition. Severe storms can cause damage to even strong healthy trees but the biggest danger is associated with root and basal decay fungi. These fungi can enter tree roots and the base of stems through damage caused by excavations, disturbance, poor pruning and even drought or prolonged flooding.

Autumn is a good time to check for decay fungi as many are only generally visible in theĀ  autumn when the fruiting bodies are produced. If you see fungi growing on or near the base of trees you should get it identified and the tree assessed by a tree expert (To be found in Yellow Pages under 'Tree Work Contractors').

The most common decay fungi are bracket fungi which produce plate-like structures or 'brackets'. The most serious of these, because the fruiting body is not persistent and can therefore only be seen in the autumn, is Meripilus giganteus, the Giant Polypore. This produces large masses of rounded, wavy edged, soft plates at the base of infected trees and on the roots. The upper surface is brownish yellow to chestnut brown when fresh and the lower surface is creamy white. With age the colour darkens and the fruit body deteriorates into a black, slimy mess especially after frost.

Meripilus giganteus causes extensive root decay in broadleaves especially mature beech and is a major cause of windblow in beech trees. Decay can be rapid and any sign of this fungus should immediately ring alarm bells. Because the fungus kills and decays roots there may be an associated decline in the condition of the crown although frequently there are few obvious signs and otherwise apparently healthy trees can fall over even in calm weather.

On close inspection of a collapsed beech in Truro in 2000, large quantities of fruiting bodies of the Giant Polypore were found. The root system was extensively decayed and the roots were like sponges.

If you are responsible for trees in prominent locations, it is important to check them regularly.