Honey fungus is probably the most devastating disease of trees, shrubs and other woody and some herbaceous plants. No plant is completely immune, but some show good resistance.
It attacks and kills the roots of affected plants, then rots the dead wood, leading to the whole plant dying. Some or all of the above symptoms may be present on affected plants.
The clumps of “honey” coloured toadstools may be the first obvious signs of the presence of honey fungus. They don’t always appear, but once they do the disease will already be fairly widespread. Also, they are often confused with other, harmless, saprophytic fungi. Luckily, the spores produced by the toadstools play little part in the spread of the disease.
It is usually recommended to search through the soil for the black rhizomorph “bootlaces” to discover whether honey fungus disease is present. However, the only sure-fire way is to look for the paper-thin sheet of white or creamy-white mycelial fungal growth that forms just underneath the bark, and which characteristically smells strongly of “mushrooms”. This forms at or just above ground level, rarely spreading higher than 1m (3ft). However, this does mean removing the bark, which will then kill the plant.