Beware the Honey fungi
By Jennifer Holmes

Beware the Honey fungi

As specialists in Invasive Native and Non-Native Species (INNS) our aim is to educate and alert the public and commercial businesses to species that can be extremely problematic, harmful to the environment or toxic to humans and wildlife. This month we’re focusing on a particular species that is extremely harmful to woodland areas – Honey Fungi.

Honey fungi – Parasitic and deadly

Honey fungi (Armillaria) – not as sweet as the name depicts – are a group of parasitic organisms that attack and kill the roots of trees, shrubs and woody perennials. They are one of the most destructive fungal diseases in the UK, with the capacity to completely fell trees! Being among some of the biggest living organisms in the world, their underground networks can spread up to 1 metre per year, often covering many miles and they can live for up to a thousand years. For these reasons, Honey fungi are a problem for landowners and homeowners alike.


As the fungi spread underground, it’s only visible above ground as a white fungal growth at the base of the tree, it also appears briefly as honey-coloured mushroom like structures (hence the name). If the ‘mushrooms’ are not visible, peeling back the bark will reveal any fungal growth underneath. Also, its red-brown rhizomorphs can sometimes be seen between the bark and the wood of trees, appearing as red string-like structures at first before turning black. But don’t be deceived by their apparent innocent appearance, the environmental impact of Honey fungi is high – it wreaks havoc among forests and woodland areas, often capable of destroying large areas of woodland at a time.


But what makes honey fungi so problematic is the fact that treatment is very limited. At present there is no chemical that successfully treats or removes honey fungus. If detected there is only one effective solution and that’s removal, and all waste material (including the plant’s stumps) must be transported to a licensed landfill site by a company holding a Waste Carrier’s Licence. Excavation really is the best choice if you want to completely eradicate the problem, and sad though that may seem, the affected trees will most likely die in any case, so this treatment will save other trees in the long-term.

The only effective alternative is to create a barrier whereby the fungi is not able to spread. This is not a cure for the affected tree, however does limit other trees being infected. This method involves implanting a rubber lining which must be buried at least 45cm down, and protrude at least 2-3cm above soil level to effectively create a barrier to the rhizomorphs.

Preventing spread

After treatment, it is important to ensure no particles or spores are accidentally carried to another site on footwear, tools or equipment, so thorough cleansing before leaving the infected site is necessary. Though this may be time-consuming, if not done correctly the spores can easily be carried offsite.

What to look out for

  • Upper parts of the tree, plant or shrub that appear to be dying off
  • Leaves that fall out of season (particularly in the Spring)
  • Cracking or bleeding at the base exposing the rhizomorphs
  • Its honey-coloured mushrooms spreading out from the base, or climbing up the trunk
  • A strong damp-mushroom odour coming from the base or in the bark

If you need any assistance identifying Honey fungi, or you know you have it and would like some advice on treatment, you can use out free identification service or if you’d like us to carry out a survey and provide a treatment programme and quotation contact us to speak to a specialist advisor.