Phaeolus schweinitzii

Phaeolus schweinitzii is a serious fungal disease of most conifer trees. It usually enters the tree via root tips and weakens the roots as it utilises the cellulose in the wood for food. It can reach right up to the base of the tree and even into the lower trunk. I have found Pheaolus high up in trees, but only rarely.

Young, yellow fruitbody





Mature brackets near base of Douglas fir.



The fungal fruitbody starts off as a formless yellow lump, growing out of the ground near a tree or else from its base or maybe from a wound on the stem. The bright, sulphur yellow colour is quite distinctive and shows that the bracket is actively expanding. These are found from May to August but older ones can last longer where they are protected from the weather. Once fully grown the yellow colour gives way to a rich brown and the top of the bracket is stiffly felty. Old fruitbodies are dull, grey or black and look very uninviting. The brackets can get up to nearly 1m in diameter but I usually see them less than half this size.

The disease is very serious and when the brackets appear it usually means that the decay is quite extensive. Trees with Phaeolus are liable to windthrow (because the roots lose their strength) or breakage on the lower trunk (because the centre of the base is so decayed that there is not enough healthy wood to deal with the stresses of the wind). It is very difficult to quantify the loss of root strength and so the appearance of the fruitbodies is a major safety issue.

Old brackets gradually disintegrate.