Honey Fungus
Honey fungus is the common name given to several different species of fungi (Armillaria) that attack and kill the roots of many woody and perennial plants. The most characteristic symptom of honey fungus is white fungal growth between the bark and wood usually at ground level. Clumps of honey coloured toadstools sometimes appear briefly on infected stumps in autumn. It’s the most destructive disease in UK gardens and it can have a silent and deadly impact on trees.
This is the interior of a recently –felled dead Beech tree, taken down to remove the risk it posed to users of a busy Basingstoke car park; the damage caused by honey fungus is evident through once-healthy wood of the trunk.
What Are the Symptoms?
Above ground, you might see:
- Upper parts of the plant die. Sometimes suddenly during periods of hot dry weather, indicating failure of the root system; sometimes more gradually with branches dying back over several years
- Smaller, paler-than-average leaves
- Failure to flower or unusually heavy flowering followed by an unusually heavy crop of fruit (usually just before death)
- Premature autumn colour
- Cracking and bleeding of the bark at the base of the stem
- If suitable conditions permit, mushrooms are produced in Autumn from infected plant material
Below ground
- Dead and decaying roots, with sheets of white fungus material (mycelium) between bark and wood, smelling strongly of mushrooms. This can often be detected at the collar region at ground level, and rarely spreads further up the trunk under the bark than about 1m (3¼ft). This is the most characteristic symptom to confirm diagnosis
- Rhizomorphs (root-like cords), which are often difficult to detect
There are no chemicals available for control of honey fungus.
If it is confirmed, the only effective remedy is to excavate and destroy, by burning or landfill, all of the infected root and stump material. This will destroy the food base on which the rhizomorphs feed and they are unable to grow in the soil when detached from infected material.
To prevent honey fungus spreading to unaffected areas, a physical barrier such as a 45cm (18in) deep vertical strip of butyl rubber (pond lining) or heavy duty plastic sheet buried in the soil will block the rhizomorphs. It should protrude 2-3cm (about 1in) above soil level. Regular deep cultivation will also break up rhizomorphs and limit spread.
For a good list of more resistant plants, go to http://apps.rhs.org.uk
All that said, the presence of honey fungus doesn’t always have to mean felling your tree. As always, any work you do should be based on the health of the tree it’s setting, the risk that it presents and the best arboricultural advice available.
For advice, information and a free quote, call Andrew on 01256 817369 or 07740 427925 or email him at andrew@primarytreesurgeons.co.uk