Q What are bracket fungi?
A Bracket fungi feed on wood, either as living trees or dead logs, and the brackets are their fruiting bodies. These form shelf-like structures singly or in groups and normally stick out from the trunk or branches though some develop from infected roots and appear at ground level. They can vary in size from a few centimetres to the giant polypore (Meripilus giganteus), which can reach 1m across. There are scores of different species including the gruesome beefsteak fungus that looks like raw meat and produces red juice when cut, and the more attractive chicken of the woods, which is bright yellow and a gourmet delicacy.
Caption: Bracket fungi are found on both live and dead trees
The website first-nature.com has a good photo guide to help you identify the different species. (Also see Professional help below).
No symptoms may appear for many years, but signs to look out for include areas of dieback, or a generally sparse appearance, trees leafing up late in spring or dropping leaves early in autumn, areas of dead bark and weeping or gumming on the trunk. Although these symptoms can indicate infection by a damaging bracket fungus, they could also be caused by drought or flooding or other types of fungi such as honey fungus or phytophthora, or other disease organisms such as bacteria. The brackets themselves may only appear for a short time, usually in autumn, or may remain all year round, gradually increasing in size, and producing spores for longer or shorter periods depending on the species.
Q What causes them?
A Brackets occur when the fungus in question has reached maturity and is ready to produce spores. Trees may be infected by the fungus for many years before brackets appear. The life cycle will vary depending on the species but most produce spores that are spread by air or water and enter the wood through areas of damage.
Q What trees do they attack?
A It's likely that all tree species will be susceptible to one or more of the many bracket fungi though beech, ash and sycamore seem to be particularly prone. Generally speaking the fungi cannot penetrate healthy bark so they attack through damage and pruning wounds. Sometimes infection can spread via the roots from an infected tree to an otherwise healthy one.
Q What damage do they do?
A Fungi are crucial to the breakdown of dead wood, and the recycling of its component parts, so are essential elements of a woodland ecosystem. Some feed only on dead wood and are entirely harmless. Others attack living trees, killing the tissues and initiating decay. Once decayed, wood had no structural strength, so trees that are badly affected in the roots or the base of the trunk (the butt) can be blown over, while those with rot higher up (top rot) can drop branches.
Q Will fungi on dead logs or bark chippings spread to live trees?
A Generally not. The species that attack live trees are different from those that normally live on dead wood. When a tree dies from fungal attack, that fungus can live on in the dead wood for a short while, but will then die out. As fungal spores can blow in from anywhere, having dead logs or bark chippings in the garden should not increase the risk of infection significantly.
Q How do I deal with affected trees?
A Unfortunately just removing the brackets will not have any impact on the growth of the fungus. If brackets appear on live trees, and especially if you see any of the other symptoms of fungal attack, then you should seek professional advice if the tree could cause damage by falling or dropping branches. Gardeners are legally responsible for their trees and could be held responsible for damage caused by falling timber. However, the presence of bracket fungi is by no means a death sentence. Not all bracket fungi are equally damaging, and trees also have the ability to compartmentalise their wood, isolating disease organisms and minimising damage. Old-fashioned treatments, such as boring drainage holes, excavating dead wood, or filling in cavities, can do more harm than good and are not recommended.
Q Can I prevent the fungus spreading to other trees?
A In practical terms it is impossible to prevent the spread of spores. Keeping your trees healthy and free from damage (see below) is the best preventative.
Q How do I avoid the problem?
A Most fungi can only enter via areas of damage, particularly pruning wounds. When planting new trees, choose ones that suit the prevailing conditions and the available space. This should minimise weather damage and mean that you do not need to resort to heavy pruning to control the size. If you do need to remove a branch, do so before it has grown too large, and cut carefully, preserving the collar at the base of the branch which will produce wound tissue to cover the damage. Wound paints are no longer recommended as they do not offer long-term protection and can make things worse by trapping spores against the cut surface.
Q How do I find professional help?
A If you need someone to visit, try Which? Trusted Traders to find companies that have been checked and assessed by Which?. Otherwise contact the Arboricultural Association (01242 522152, trees.org.uk), which produces lists of approved consultants to give advice and contractors to do practical work.