Cauliflower fungus is parasitic on pines, but will not necessarily kill the host tree.
Dick Alder
Brian Spooner began his talk by suggesting that there is a lot of unnecessary fear of fungus amongst tree owners. It is not generally understood that fungi belong to their own kingdom and, unlike higher plants, they cannot make their own nutrients, but must take them from other life forms.
But they are not all parasitic by any means: around 90% of plants enter into a mutually beneficial arrangement with fungi, known as a mycorrhizal relationship, in which the fungus provides nutrients and drought protection to plant rootlets in exchange for the requirements for its own growth. The mycelium of the fungus can easily be seen enveloping tree rootlets, turning them into 'digits' rather than strands. It does not penetrate the plant cells. This kind of relationship may have been present for a billion years, and is thought to have been a catalyst for the move of life from the sea to the land. There are actual fossils of mycorrhizal fungi which are 400 million years old. The main families of fungi forming tree mycorrhizas are the Amanitas, Boletes, milk caps, Russulas, and Cortinarius (familiar to anyone who has been on a fungus foray). The latter two groups are exceedingly difficult to identify to species.
A literally overlooked group of mycorrhizals are the truffles. They are amongst 80 species of British fungi which fruit underground, undetected except by smell; this is picked up by mammals, which consume the fruit body then disperse its spores in the obvious manner. However, in this country we do not seem to find truffles to match those Perigord ones which fetch six-figure sums! Note that fungi are food for many creatures, especially mammals, insects and molluscs.
Another major section of the fungus kingdom is responsible for recycling dead plant material. Without these saprophytic fungi, it would just pile up and not be broken down for re-use as nutrients. They break down cellulose and lignin into fine white and brown rots. Some species are known to be present in the living plant, but only become active after it dies, and it may be that the fungus protects the plant from other predators up to that point. Some familiar saprophytes are the big dryad's saddle fungus on various trees, velvet shank seen in midwinter, Jew's ear, often on elder, and cramp ball on ash. The little candle snuff fungus produces zone lines in dead wood, which when cut and polished gives rise to the ornamental feature known as spalting.
Brian is pursuing a phenomenon which he has noticed, where small rodents appear to be eating the black, carbonised fruit bodies of an encrusting fungus called Eutypa, on dead sycamore branches. No previous literature has been found describing this activity. Woodchip mulching, as practised more and more over the past 20 years, has brought about an explosion of associated fungi, now around 250 species, some previously unknown to science and many new to Britain.
The third type of fungus is the one which tree owners and gardeners may sometimes have cause to fear, but maybe not as much as they think. Parasitic fungi are found on all parts of plants, including the leaves. In fact, new species are turning up on the leaves of trees and plants in Britain on a regular basis. Many others have long been familiar, like tar spot on sycamore, or the powdery mildew on young oak leaves, and moulds often affect fruits.
Cauliflower fungus is parasitic on pines, but will not necessarily kill the host tree.
But the dreaded parasitic fungi are often the large brackets on certain trees. One of the worst is the colourful, bright yellow Phaeolus on conifers of many kinds. It has caused the removal of three of the four great cedars at Claremont recently, and threatens others at Painshill. The giant polypore is similarly bad news for beech trees. These two are root parasites, which starve the tree of nutrients. Honey fungus is a dread name (usually misapplied) for a group of six species of Armillaria, not all of which are dangerous.
But some of our common brackets are much less dangerous, despite appearances. Weeping polypore on oak is one such, cauliflower fungus on pine is another. They may kill a tree, but will not necessarily do so. The 'artist's fungus', Ganoderma, is a big but particularly mild parasite on many old trees. The birch bracket, Piptoporus, is thought to kill only trees that are already weakened. The beefsteak fungus, Fistulina, found on oak and chestnut, is only involved in removing heartwood when it has lost its purpose, leaving a hollowing tree to decline slowly and gracefully. And the sulphur polypore, Laetiporus, the brilliant yellow brackets of which are frequently seen on a range of trees, is also involved in the hollowing process. The huge Keffolds yew at Haslemere was sprouting this fungus in 1901, yet it is still a superb, healthy tree!
So Brian's message, in this age of health and safety, is: “Woodman, spare that tree!”.