Honey fungus Armillaria is the common name given to several species of fungi of which seven are present in the UK. Only two of these are thought to be aggressive pathogens of healthy trees, Amillaria mellea and Amillaria ostoyae, others will only infect trees that are already suffering due to disease or environmental stress.
Honey fungus will attack and kill the roots of woody plants, spreading underground by direct contact from infected roots to healthy ones. It can also send out root like structures that are black in colour called rhizomorphs (bootlaces)these can spread up to 1 metre a year (usually in the top 15cm of soil) this gives the ability to attack trees a great distance from the source of the infetion.
Cause
The parasitic fungi Amillaria, originating from dead stumps or old roots left in the ground
Symptoms
The base of the trunk, below ground, will have sheets of white fungal mycelium between the bark and the wood, roots may appear slimey and have a mushroom smell.
the bark may crack and bleed at the base of the stem
Leaves may appear paler and smaller than normal
The tree may produce more flowers or fruit than usual, it may not flower at all
Parts of the tree may die, indicating a problem with the roots
Honey coloured toadstools with a white rig on the stem, usually found around the stem of the tree, the caps can be 10-15cm in diameter. These will produce spores. The toadstools may only appear for a few days but it can be anytime between late summer and early winter.
Sudden death of a tree.
There are no chemicals available to control the spread of honey fungus. Root barriers can be placed in the soil up to 45cm deep to help stop the spread of rhizomorphs.
Remove infected plants, careful not to drop infected soil in other parts.
Keep all other trees well fed and watered, a healthy tree is much more able to withstand attacks.
Replace with trees that are more resistant to the disease, Acer negundo, Juglans nigra, Quercus, Cercis, Catalpa, Bamboo, Rhus