Honey fungus, which is often diagnosed at the end of summer when trees and shrubs suddenly die back, or at the start of autumn when honey-coloured toadstools appear, attacks and kills the roots of many woody and perennial plants. These plants require removal but the disease is extremely hard to eradicate as it lives within extensive root systems underground and can spread to nearby and replacement plants.
To understand which plants were prone to the disease, a team of RHS pathologists compared more than 5,000 records of confirmed cases of honey fungus from its members and a study into susceptibility by the University of California. It grouped plants into three categories according to how often the disease was reported on them, adjusting the score to account for their popularity in UK gardens based on RHS data.
Plants in the Myrtales order of flowering plants – including myrtle and fuchsia – and Ericales – including camellia and heather - tended to have low susceptibility, while those in the Saxifragales – such as liquidambar and witch hazels - and Fagales – birch and sweet chestnut - were mostly highly susceptible.
The RHS is now advising gardeners that if honey fungus is diagnosed on their plot, or their neighbours’, that they consider planting those deemed to have low susceptibility, helping to limit its spread and maximise enjoyment of the plant.
Popular garden plants and their susceptibility to honey fungus include:
A complete list of plant susceptibility is available on the RHS website: www.rhs.org.uk
Honey fungus has topped the RHS annual pest and disease ranking for 23 years and has been exacerbated in recent years by warmer, drier summers that increase the stress levels of plants and make them more susceptible to attack from the disease. Taking into account the optimum conditions for a plant, such as soil preference and access to light, can also help to make it more resilient.
Matthew Cromey, Senior Plant Pathologist at the RHS, said:
“The RHS has long advised on what plants might be best avoided if honey fungus is a known problem on your plot but this new research, for the first time, also accounts for a plant’s popularity in gardens and therefore the diseases’ likely true impact. Following the planting advice isn’t a guarantee against the disease but a sensible precautionary measure akin to practicing good plant hygiene.”
The RHS has updated its honey fungus advisory pages at www.rhs.org.uk
where more information can be found about the various strains of disease and management techniques.
‘Susceptibility of garden trees and shrubs to Armillaria root rot’ was originally published in the journal Plant Disease