As soon as there is damp weather in the autumn, toadstools start to appear all over the garden. Most of these fungi are perfectly harmless, some even beneficial, but there are a few which strike terror in the heart of even the most experienced gardener. Top of the list of the Fungal Chamber of Horrors has got to be honey fungus, Armillaria. The toadstools with their classic yellowy ginger honey colour are enough to bring tears to your eyes…. especially if you love trees and shrubs!
The toadstools generally only appear in the autumn, often with several flushes and often being temporarily wiped out by the first frosts. There are several different species of honey fungus and these vary in their aggressiveness or ability to attack – some are pretty weak and may only live on materials such as dead stumps, but others have a distinct attraction to living woody plants. Bear this in mind when you spot the toadstools – they may not mean you have a disaster on your hands. Indeed, honey fungus is so widespread that if were always as damaging as some would have you believe, we would all have concreted backyards!
Recognising honey fungus
The toadstools most commonly grow in clumps and usually have a distinct ‘ruff’ close to the top of the stipe or stem (this marks the point where the stipe and cap of the fungus were once joined). The majority of fungi have dark spores, honey fungus spores are white. Look carefully at the lower fungi in the clump and you may see spores from upper fruiting bodies – this looks rather like a dusting of icing sugar. You could also make a spore print, carefully remove e recently opened toadstool, cut off the stem and place the cap, gill side down on a piece of dark paper. Overnight a clear spore print should develop.
A bit of excavation may also be in order as you may then find the underground rhizomorphs or bootlaces. The very tough fungal strands are near-black or a reddish brown and if you cut one open it will be white inside and smell distinctly of mushrooms. These grow at about 1m a year and are the main means by which the fungus can move from one host to another. Infected roots also show tell-tale signs – lift some of the bark and sandwiched between this and the woody part of the root you will find a creamy white fungal sheet. This is the mycelium and it is the most active area of the fungus. It is often found around the collar or base of the tree or shrub, and occasionally many feet up the trunk too.
What might confuse you? There are large numbers of similar coloured toadstools so check carefully. Some, such as the sulphur tuft, Hypholoma are harmless or indeed may be beneficial to a tree and are often found close to trees. White fungal strands found in the soil and sometimes attached to dead pieces of wood or root, often cord fungi, are not honey fungus and need not worry you.
What can you do about honey fungus?
If in doubt get someone to check the evidence for you. There are no chemical controls available. If trees, shrubs or other woody plants are deteriorating as a result of honey fungus you will need to remove them, and as much of the root system as possible. Leaving infected plants in the garden will increase the chances of the fungus spreading. This may mean employing a tree surgeon complete with winch, or perhaps a stump chipper and then following up with plenty of ground clearing later on. Try to keep plants in as healthy and vigorous a condition as possible, so they are more resistant.
Avoid replanting with things known to be especially susceptible such as privet, wisteria, lilac, cedar, roses, rhododendrons, apples. If you need woody replacements consider less susceptible plants such as yew, beech (both good for hedging), cercis, catalpa, fothergilla, hebes, pieris, rhus, choisya and chaenomeles.
But most importantly : Do something, don’t be lured into thinking that rotting wood is a great wildlife habitat and tree stumps are the thing to have…because leave the infected stump in your garden and you’ll be leaving behind the fungus and pretty well inviting it to devastate your garden!