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Recognising Honey fungus and what to do about it

Posted on 12th October 2016

Honey fungus is the dreaded fungal disease that seriously affects and often kills a wide range of woody plant species. It is very difficult to eradicate once you have it and stopping the spread can only be achieved with early recognition and fairly drastic action.

Many fungi work in harmony with plants and are a great benefit in breaking down organic matter in the soil and releasing nutrients that the plants and trees can then use, this is an essential part of the carbon cycle and the decomposition process otherwise plants would not be able to access nutrients locked up within organic matter, these beneficial fungi are known as ‘symbiotic’ because both the fungi and the plants benefit from the relationship, the fungi taking small amounts of sugars from the plant roots which they are not able to generate themselves.

Honey fungus is unfortunately a highly pathogenic type of fungi that will attack many different species. There are no known species that are fully resistant but the RHS have produced a list of plants that are rarely reported as being attacked and the theory is that these plants may have some resistance and could be considered when replanting an area that has been affected by the disease.

The list (which includes a list of plant species most frequently attacked (and therefore to be avoided in infected areas) can be found at:  https://www.rhs.org.uk/advice/pdfs/honey-fungus-host-list

The fungal fruiting bodies (the toadstools) that produce the spores are seen during the autumn, mainly during October & November so this is the best time for early detection but unfortunately the rest of the year is more difficult. The toadstools usually form in a dense cluster and are golden brown coloured, and are around button mushroom size when they first emerge, opening out to around 5-8cm across and 15-20cm tall with a fairly flat cap when fully open. Other signs can include dieback of part or whole branches, spreading steadily through the plant and peeling dying bark exposing the dead wood inside. The leaves may be small and fall early accompanied with either poor or excessive flowering. In advanced cases there will be a white mass of fungal mycelium at the base of the trunk under the bark and around the roots, and the classic black ‘bootlace’ rhizomorphs may be seen spreading in the soil and under the bark, these are the main cause of the spread of infection and can rapidly colonise ground many metres away from the source of infection.

If you spot a plant that is suffering from the fungus, there is not a lot you can do to save the plant unfortunately, the best advice is to remove the tree or shrub and as much soil around it as possible. Burn the remains if possible. Search for rhizomorphs radiating from the infected plant and remove them, it is best to remove and replace all soil from any area that has been infected. If this is not possible then you should replant with a range of species recommended by the RHS that could have some resistance. There are no longer any chemical controls for the disease.

Sadly, the original Bramley apple tree in Southwell Nottingham, recently shortlisted for 2016 Woodland Trust tree of the year and a big part of our production heritage, is suffering very badly from this disease. At over 200 years old it has had a good innings but it clearly a popular ‘people’s choice’ and will be a sad loss – the good news is that many cuttings have successfully been taken.