There are six species in Britain,
two of which cause serious damage; A. mellea attacks mainly
broadleaved trees and shrubs; A. ostoyae affects conifers.
The foliage wilts, turns yellow and there is premature
leaf fall. Dieback of individual branches occurs, leading
to the death of the whole plant which can happen over
a period of two weeks to several years, depending on the
maturity of the plant. There may be cracks in the bark
at the base of the trunk, with an exuding sticky substance.
(This cracking can be the symptom of the root-rotting
disease, Phytophthora).
A clump of large, yellow-brown to dark brown, mushroom-like
growths covered in darker hairy scales, emerge from the
base of the stem or trunk in the autumn. The gills are
cream with a pinkish tinge at first, turning yellow-brown
with scattered darker spots. These are the fruiting bodies
which produce millions of spores, but are not the main
means in infection.
Not all honey-coloured fruiting bodies are honey fungus,
look for a white collar below the cap and a yellow to
honey-coloured downy stem. The flesh is white and can
be cooked (bitter if uncooked), but is not a great delicacy.
Black, flat rhizomorphs with white centres, which resemble
boot laces, radiate underground from an infected tree
or stump and are the main means of further infection.
These are fragile and can be difficult to find, larger
ones of less virulent species (pictured) are more easily
spotted. They can spread for about 7 metres to a depth
of 70cm.
When a new host is reached, white sheets of the mycelium
grow up the stem or trunk under the bark for up to several
metres. A method of confirming an infection is to peel
off a little of the bark to reveal the white mycelium
which has a mushroom smell.
Remove any infected trees or stumps and their roots
with as much soil as possible, dig a trench about 70cm
deep around the area and pour in some diluted formalin
or Armillatox as a sterilant. A vertical barrier of
plastic burried to a depth of one metre around the affected
tree, should halt the spread of the rhizomorphs.
If a hedge is infected remove a healthy plant on either
side of the infected ones.
Unfortunately from July 2003, new EU regulations requiring
expensive licensing and registration mean that Armillatox
will no longer be available. Jayes Fluid is a similar
product and can still be used as a disinfectant.
As with all diseases good garden hygiene is the best
way to prevent infection, so remove stumps of trees
and shrubs which could be open to the disease. When
preparing ground for planting remove any old roots or
pieces of wood.
Some trees and shrubs are more resistant to Honey fungus,
eg. yew, beech, hebe and cornus.
