Armillaria (Honey Fungus) – Ignore it at Your Peril
I have visited many gardens this year and throughout the month of October, I am always on the lookout for clumps of honey brown mushrooms. Due to the summer, we have experienced, I have unfortunately identified many cases of Honey Fungus in gardens, one of which was suffering from a severe infestation in an established Privet Hedge.
I was dismayed to hear, on a well-respected garden show, a mushroom expert advising that one should let honey fungus run its course; however, this was in a woodland setting, and it is not advice that I would advocate for domestic gardens.
Honey Fungus of the Genus Armillaria has seven species in the UK, the most destructive being A. mellea and A. ostoyae. Symptoms are:
- Clumps of honey brown fungus (these are the fruiting bodies that spread the spores).
- Sudden weakness and death of mainly woody plants that have otherwise been healthy.
- A white mycelium beneath the bark from underground level to approximately one metre up the stem.
- The presence of black root-like structures called rhizomorphs (boot laces) below soil level.
Alas, there is no chemical control for this fungus, but all is not lost. Prevention is better than cure and if you are having trees or shrubs felled, have the stump completely dug out or at least remove as much possible, especially if the tree or shrub is suffering ill health.
If you can identify an infection often shown by the presence of mushrooms, it probably means there is a rotten stump underground. This should be dug out in order to remove the source of nutrients that feed the boot laces preventing their spread to the next victim. Deeply cultivate around the growth of the mushrooms to disrupt the life cycle of the bootlaces. In extreme cases and to protect valued plants in the vicinity, a root barrier can be inserted to a depth of at least 45cm.
I was asked to visit a garden that had serious issues on a previously healthy Privet hedge. On arrival, I observed a patch of Honey Fungus around two metres from the hedge where the owner had removed a rather sick willow (Picture 1).
On inspection of the hedge, some of which had been cut back, more fruiting bodies were observed, Pictures 2 and 3.
The only option was to completely remove the hedge and soil to a depth of 60cm, insert a root barrier, refill and replant.
As the strapline said, “Honey Fungus, ignore it at your peril.”
Please follow the link below for a list of woody plants resistant to Honey Fungus.
Steve Malsher heads up the Specialist Project Team, teaches the RHS Level 2 at Nicholsons and is happy to advise on pests and diseases.