Honey fungi, Armillaria, are a group of parasitic fungi. They attack trees, shrubs and woody perennials, and are one of the most destructive fungal diseases in the UK.
They are also among some of the biggest living organisms in the world, their underground networks often covering many miles and living for up to a thousand years.
It is so successful because, unlike most parasites that rely on keeping their hosts alive in order to extract nutrients, it can kill its host and continue living on the decaying matter for many years. Watch our video on how to diagnose honey fungus
The fungi spread by long root-like rhizomorphs that live close to the surface of the soil, which are reddish brown when new and turn black as they mature.
They attach themselves to the root collar of woody plants, killing off the root systems leaving the host unable to absorb nutrients and water.
Honey fungus symptoms
- The die back of upper parts of the plant. This can happen quickly particularly in hot dry weather, or may take years to gradually kill off branches.
- The leaves may fail to develop in spring, or be smaller and paler than usual.
- The plant may fail to flower, or in some cases suddenly flower and fruit profusely before dying.
- There can be signs of cracking and bleeding at the base of the trunk or stem. The red-brown rhizomorphs can sometimes be seen between the bark and the wood of trees.
- The fruiting bodies of the fungi are honey coloured toadstools. They may be seen in autumn growing on infected wood, at the base of a tree or on a nearby stump.
- Below the ground, the tree roots steadily rot from the ends inwards.
- The base of the trunk is often covered in white fungal strands (smelling strongly of that damp mushroomy odour) that can spread up between the bark and the wood, in severe cases for up to a metre.
Treating honey fungus infections
At present there is no chemical fungicidal control for honey fungus.
If it is identified in your soil, the only solution is to remove ALL infected material (or as much as you practically can), including stumps and roots. Then destroy all of this material by burning.
The fungus cannot survive on its own in the soil without its host. To ensure that you don’t accidentally give spores a fresh host, it is vitally important to disinfect all tools after removal of infected material.
Preventing the spread of the fungus from an infected area is labour-intensive, but may well be your only course of action. You need to contain the fungus by burying a butyl rubber lining at least 45cm down, and which protrudes at least 2-3cm above soil level. This creates a barrier that the rhizomorphs cannot penetrate.
Once you have removed an infected plant or created a necessary barrier it is then possible to replant with a more resistant species.
Resistant plants
No woody plant is completely immune to attack, but if you think that your garden has honey fungus, then there are a number of trees that are judged by the RHS to have good resistance levels. These include: Juglans nigra, Carpinus betulus, Larix, Quercus ilex and Taxus.
And shrubs showing good resistance include: Berberis, Buxus sempervirens, Philadelphus, Sambucus, Lonicera nitida and Griselinia.
Should gardeners live in fear of Armillaria?
In my personal opinion, having lost a couple of trees down the years to it (a lovely opportunity to grow something else, as far as I’m concerned), not really. It is found in practically every location that has groups of mature trees and rotting wood on the ground, and in the wild it is “in balance” with all sorts of other organisms, playing an essential role in the ecological turnover of forests. When it flares up badly in gardens, which is not common when one considers how widespread it is, one of the main reasons is that this wild ecosystem is mostly absent, and the soil life has been punished with fertilisers, pesticides, tilling and digging, and the incessant removal of weeds and debris, leaving bare soil. It is orchard owners and forestry managers who have a real cause for concern, firstly because it’s their livelihood, and secondly because man-made monocultures create the conditions where any pest or parasite can go berserk on the banquet before them, with no biological bouncers to bring them back into ‘balance’.
Have you had any first-hand experience of dealing with honey fungus? Please do let us know in the comments box below.
Killed off mature Walnut in my gardenseveral years ago, followed by Eucalyptus gunnii and two silver birches, hawthorn then pyracantha. Armillatox, which is now prohibited for garden use, seemed to help a bit. Other eucalypts have not, so far, been affected. That’s most of my 100′ square back garden infested. Other trees alongside road at the front also affected, one died last year with incredible amount of fungi sprouting this year. Presumably it is pretty rife throughout our neighbourhood which was originally uncultivated parkland
I think the RHS list is a guide only. The fungus is attacking my elder tree and some bamboo, both of which are supposed to more resistant.
I’ve put down some early purple orchid (orchis mascula) seeds because it controls the fungus. If only they would grow more easily …
Hello, i had a log pile at the back of the garden where I was going to make a fernery from the logs I had collected. A year later I’ve noticed long bootlace rhizomorphs spreading a metre or so around the log pile under the weed matting I’d our down around it. They look exactly like honey bootlaces but they are white, slightly orange in parts. Can they be white when very young? I fear I may have introduced it into my garden and if so I want to act fast!
I’ve removed all the logs and started removing some soil as I’m fearing the worst, but it would be good to know for sure if It’s honey fungus rhizomorphs!
Hi Sarah, I fear you may have been overcautious, and thrown away a thriving woodland fungus community of harmless saprophytes that, ironically, play a big part in keeping honey fungus and other xylophagous fungi under control in the wild. Young honey fungus rhizomorphs are a ruddy brown/purplish colour, turning black as they mature. With that said, there are at least 7 Armillaria species in the UK, and I have not seen examples of all of them: still, I can’t see any mention of pale rhizomorphs associated with these fungi in my reference library. You see sheets of white mycelium under & on the bark of living plants that are being consumed by Armillaria, not – to my imperfect knowledge – elsewhere.
Fungal disease has destroyed most of my small garden in a very short time. Have tried all the measures and treatments recommended – to no avail. An expert gardener has looked at the garden and is convinced that my proble is caused by Honey fungus disease.
Every page od advice I read says that nothing can treat this disease. At the moment only the rear garden is affected, leaving the unconnected (ie no soil bed beteen) front garden unaffected. My real fear is that the front garden will get destroyed as well. Can it spread passed the house and driveway?
Thank you for your question and apologies for the delay – we have been buried in getting our new site up and running…
1. Bad news/good news. Bad news – Honey fungus rhizomorphs (root equivalents) grow by about a metre a year. So a fungus can increase in size by 2 metres from one side to the other. Good news – The rhizomorphs grow in the top 15cms or so of soil. So if your house has foundations and if your drive is well made with scalpings or the like under the concrete/asphalt/whatever then IF it is honey fungus you front garden should be safe.
2. However you say that
–
a. I have no idea what size very small is, but if your garden is as wide as a small house it will still be 4-5 metres across. Which is 4-5 years travel time even for a hungry honey fungus and this one, if it eating your plants as it goes is not too hungry.
b. So I do not see how it could have happened in less than 4-5 years and some plants larger trees for example can take a few years to succumb. Does this correspond with your “very short time”?
c. I have lived in a house with a garden that while quite long is not much more than 7-8 metres wide for most of its length. We have been here for 23 years and honey fungus has been here a bit longer. We lost a silver birch in the second year (2002) and a crab apple (Evereste which is my favourite) we planted in 2005 has just died. It killed a rhus – which is unusual – about 10 years ago. On the other hand more susceptible plants seem perfectly happy. The quince (next to the rhus – I think it is Serbian Gold) is going strong as are our roses, wisteria(s), jasmine, apples, aucuba, camellias and honeysuckle that used to grow into the silver birch. To say nothing of the pyracantha that was planted in the hole left when we ground the stump out.
What I am trying to say is that honey fungus does not kill everything in its path nor does it do it overnight. It kills stressed and unhealthy plants. If you have it, (double check as shown in this video) the best thing is to learn to live with it. So build a bigger compost heap and use it to improve your soil year in and year out. And choose plants that grow happily in the soil type and situation of your garden.
I hope this helps
Good luck
Mature (30 years plus) winter flowering Cherry lost all of it’s leaves about one year ago.Have now felled the tree. Did not take much notice until toadstools appeared at the base of stump. I have removed the stump and most roots. But in comparison to known symptoms there is no bootlaces or a strong smell and only half of the roots seem to be affected.
think this may be a reaction to the way you treat your garden. Have you been using chemicals or removed other fungus that is supposed to live naturally in your garden? The honey fungus is a natural part of the eco system, and it will appear in cultivated gardens that are not treated the way the need to be.
It’s probably there to balance out the harm you’ve done to your garden, which may take some years, so you could just leave it and let it do it’s job.
I have a hawthorn hedge planted in a row of oak trees. Sections of the hawthorn 2 or three plants are totally dead an pull out of the ground fairly easily, there is no sign of fungus just litchen type growth on the branches but the main body is very soft internally when pulled up.
Some branches on the oak have died but not sure how serious until the buds break into leaf.
At a loss to know if this is honey fungus or something to do with a very large fairy ring nearby
Too many variables I am afraid as it could also be related to the oak trees which may have one of the root rots – on which we are not qualified to advise. We have a honey fungus advice page at https://www.ashridgetrees.co.uk/gardening-advice/plant-diseases/honey-fungus-armillaria-mellea. Best thing to do is to call a local tree surgeon out to have a look. They will give you free advice and a free quote…
Good luck
Is there any way of testing the soil before planting another tree in a nearby area to the killed off apple tree.
Thanks for your email.
I don’t think there is anything available to test for the presence of honey fungus. And, to be honest, although a tremendous amount is talked about “bootlaces” in the soil, I have seen any number of honey fungus victims and am still waiting for my first bootlace sighting. So, loads of good compost, follow good planting practice, keep the new plant well watered and stress free until it is established and try not to plant sepcies that are especially prone to honey fungus.
Good luck
A 100 yr old apparently healthy Hornbeam fell during the night into a school playing field. Falling the opposit way would have demolished the bungalow in which I live. The debris was examined and determined by DEFRA test to be honey fungus.
Over the past 2 years an adjacent cypress hedge has died one tree at a time, now at 20 metres 40 metres to go. I cannot stop it. All supposedly resistant trees and shrubs planted in the old Hornbeam area have died, except for one apple tree which is still struggling.
What can I do……?
Thank you for your comment. Honey fungus is indeed a difficult imposted to deal with. The best we can suggest is to point you to our advice. Wishing you success. Kind regards Ashridge.
Hello there, I have honey fungus in my cottage garden and had to cut down some trees. But I am not feeling aggressive against the fungus and would like to know if there would be a way of encouraging other types of fungus in the garden to compete with the existing honey one… Who knows there may be a type of fungus that feeds on honey fungus. Thank you for your time if you find someone to answer me! I would be most grateful.
Thank you for your comment. Honey fungus is indeed a difficult imposter to deal with. The best we can suggest is to point you to our advice. Wishing you success. Kind regards Ashridge.
Thank you for your comment. Honey fungus is indeed a difficult imposter to deal with. The best we can suggest is to point you to our Honey fungusadvice. Wishing you success. Kind regards Ashridge.
Thank you for your comment. The best we can suggest is to visit our advice . Kind regards Ashridge