Honey fungus is a potentially fatal disease that affects trees, shrubs, woody climbers and, occasionally woody herbaceous perennials. The disease spreads from living trees, dead and live roots and stumps by means of black, stringy fungal strands ('bootlaces'). An infected tree will die once the fungus has girdled it or when extensive root death has occurred. This can happen rapidly, or may take several years.

Initial symptoms of honey fungus infection include the dying back of leafy branches or failure of leaves to appear in spring. Black bootlace-like strands appear under the bark and around the tree, and honey-coloured toadstools grow in clusters from the infected plant in autumn, dying back after the first frost. Other signs include thin sheets of cream coloured mycelium, giving off a strong smell of mushrooms, beneath the bark at the base of the trunk or stem, sometimes extending upwards, or a gum or resin exuding from cracks in the bark of conifers.

Control

Dead wood in the soil acts as a food source for this fungus, so a certain amount of control may be achieved by routinely removing any dead woody material such as stumps and roots from the garden. The best defence against fungal attack is to ensure plants are kept healthy, by correcting any drainage problems and adequate feeding and mulching. Old and sickly trees and shrubs are more vulnerable than vigorous young plants.

Any plants that have been affected should be dug up and the roots or stumps removed and burned. Areas affected by honey fungus should be replanted with non-woody species, or by species showing resistance, such as yew, dogwood, and beech. Fruit trees and bushes should not be grown on areas known to be infected, and particularly susceptible species such as birch, cypress, lilac, pine, privet, walnut and willow should also be avoided. Without host plants the fungus will eventually die out.