CHAPTER XXII

FUNGUS GROWTH ON TREES

Some fungi attack living wood, some dead, and some both; and, while the majority are found growing on the stem, others attack the twigs, leaves or root. They are of all sizes, from the almost microscopical to the beefsteak fungus, which often exceeds a couple of feet in diameter. Some are jelly-like in consistency, others leathery or almost woody in texture; and while certain kinds spring up and disappear in a few days, others remain intact on the tree stem for several years. In shape, too, they vary considerably, from the curious Jew’s ear fungus, which greatly resembles the human organ, to the giant puff-ball, that sometimes measures four feet in circumference. Then the cup-shaped and parasol fungi are appropriately named, while the flat, shelf-like arrangement of a species that frequents the oak and elm has interested many a casual observer. Excepting perhaps green, they are found of almost all colours from dull brown to the brightest crimson, while beautifully spotted and mottled kinds are not uncommon.

Healthy trees growing under normal conditions are little affected by fungi, whereas such as are predisposed to infection, by unsuitable soil, excessive drought or dampness, injury by accident or otherwise—in fact, those in a weakened condition however brought about—are, of course, far more liable to attacks. Though certain species of fungi only attack dead and decomposing wood, and are, therefore, the consequence and not the cause of disease, there are others, fortunately fewer in number, that attack healthy living trees and are the direct cause of disease and death. The prevention and extermination of fungus pests is by no means an easy matter, but by keeping the woods free from dead and dying trees and branches, and by giving immediate attention to outbreaks of the malady, much harm may be averted.

[Illustration: LARCH CANKER]

In the following notes, only the most serious cases are dealt with, or, in other words, such fungi referred to as are commonly met with and cause most damage to our woodland trees.

=Larch Disease.=—In all probability the larch disease or larch canker owes its origin to the minute spores formed in the fructification of the now well-known fungus—_Peziza Willkommii_. It has been pretty conclusively proved that these spores can only find a footing where the rind of the bark has become in some way injured, such as might be occasioned by the puncture of an insect, by wind, frost or from many other causes. The spores send down their germ tubes into the cambium, between the bark and the wood, where the moisture and nourishment afforded causes rapid development of the fungus. This soon spreads to the cells of the wood, and the annual layers either entirely cease to grow, or become disorganized and crippled in growth, causing a hollow appearance of the stem at the point of attack. The surrounding bark, by its attempts to heal over the wound, causes a thickened or burly appearance of the trunk, thus imparting to affected trees the cankered, swollen and distorted look that is so distinguished a characteristic.

The disease appears in this country on the larch, both common and Tyrolese, at all stages of growth up to thirty years, but rarely after that age. I have examined a plantation of only four years’ growth sadly infested by the _Peziza_ whereas, in other cases, the trees may be fully twenty years old before being attacked.

=Cause.=—Under what conditions of growth the larch is most susceptible to the _Peziza_ is still a matter of vague uncertainty, but there can be little doubt that an enfeebled constitution, as fully explained in the article on the larch “Trees for Economic Planting”, aided by our peculiarly erratic climate, has much to answer for. The variableness of our spring weather is, no doubt, one of the predisposing causes of disease, for, although no degree of frost experienced in this country can injure the tree when leafless, yet few are more sensitive when in young foliage.

Bearing on the subject of the larch disease, I have communications from almost every part of the country, and have personally visited and examined many of the worst infested plantations, particularly in England and Wales. Soil, if we exclude peaty, would seem to have little or nothing to do with encouraging the disease, as I have found it equally virulent on dry, sandy and heavy damp soils, but worse on chalk. Curiously enough, the disease is hardly known in the peat bogs of Ireland, and there the rainfall is excessive. It is equally strange that it first made its appearance in the Eastern and drier parts of England, and gradually proceeded to the more humid West. I have, however, noticed it in certain low-lying still, and damp portions of some woodlands, and where frosts would be most prevalent, but such cases are not general.

=Remedy.=—Several remedies have been more or less successfully tried with a view to getting rid of the disease on trees, such as by cutting and scraping out the injured portions, and applying a suitable dressing; but such remedies, although suited for single specimens, cannot be applied to a whole area of infested trees.

Under exceptionally favourable conditions, I have found the larch to outgrow the disease, though the cankered, swollen stems are never afterwards of great value for constructive purposes. Prevention in the present case is undoubtedly the best measure, for when once it has made headway, the larch disease is most difficult to cope with. By planting only sound, healthy trees, with uninjured roots in the most suitable soils and situations, and retaining these in as healthy a condition as possible, can we guard against attacks of the disease. Hardwoods mixed with the larch are to be recommended.

_Polyporus squamosus_ attacks the elm and other hard-wooded trees and rapidly brings about decay. It is one of our commonest species on diseased trees.

The =Sycamore Fungus= (_Rhytisma acerinum_).—Every one interested in trees must be familiar with the conspicuous black, pitch-like spots which so mar the appearance of sycamore leaves. These are due to the above-named fungus which, appearing as small yellowish spots on the undersides of the leaves towards the end of June, gradually increase in size and intensity of colour until they attain to fully half an inch in diameter and are inky black, with a margin of dirty yellow. The attacked portion of the leaf becomes wrinkled and much thickened in texture, while all the affected foliage drops off prematurely. After lying on the ground during the winter, the thread-like spores are produced in large quantities at the time when the foliage of the sycamore is appearing in May and June. The sycamore is not the only tree affected by this fungus, for the Norway Maple and our native _Acer campestre_ are equally liable to attack, and have in some instances suffered very severely from this cause. The fungus is becoming more plentiful, and it disfigures the maple and sycamore leaves to a wide extent.

[Illustration: POLYPORUS SQUAMOSUS (ON ELM TREE)]

_Rhytisma punctata_ may at once be distinguished from the above species by the many small black spots studded thickly together, which combine to form the large conspicuous blotches for which affected trees are remarkable. Both species are sometimes found on the same leaf. As the attacks of this fungus continue from year to year, and cause almost every leaf to drop off prematurely, the health of the trees is greatly impaired, and they become an easy prey to the still more destructive coral spot fungus, _Nectria cinnabarina_. By burning the leaves affected with _Rhytisma_ before the spores are liberated in spring, the spread of the fungus is prevented in a simple and effective manner. The sycamore fungus is very plentiful on trees around London.

The canker of hard-wooded trees is brought about by one of the Nectria (_N. ditissima_), and is very common in every part of the country, affecting the oak, beech, ash, sycamore and fruit trees generally. The ash perhaps suffers most, the timber turning black and being quite unfitted for structural purposes. It is strictly parasitical, growing on wounded portions of the stem and branch, and spreads with great rapidity, attacking trees of all ages. We have known the trees in a plantation of ash to be quite destroyed by this canker, which attacks most freely those growing on wet, sour land. This should be a warning to planters to avoid such soil.

The =Red-rot Fungus= (_Fomes annosus_ or _Trametes radiciperda_) attacks the roots of several species of pine, particularly the Scotch, Corsican and Weymouth, as also the Spruce and Silver Fir. It is probably the most destructive of the family, attacking living roots and spreading rapidly from tree to tree. The trees, when affected, quickly turn sickly and die, the wood becoming spongy and of a brownish colour, with distinct black spots. The only remedy is to take out affected trees and burn them root and branch, replanting the ground with beech or elm. Though one of the most destructive fungi in coniferous woodlands, its attacks are by no means confined to these alone, since it is found on the roots of several hard-wooded species, such as the filbert, hazel, birch and beech. Quite recently a nut plantation in Kent suffered severely from the attacks of this fungus, whole lines of trees being killed outright before the cause was detected. It spreads quickly underground from tree to tree, and unless eradicated, as it may easily be by uprooting affected trees and carefully destroying the mycelium, much damage may result.

The =White-rot Fungus= (_Fomes igniarius_) is usually found on hard-wooded trees, and takes possession of wounds that may have been occasioned by the accidental breaking of a branch or stem injury. Oak trees suffer most from the attacks of this fungus, which is often as large as a foot across, and of a brownish colour. It is named igniarius on account of the inner surface being used as tinder, when prepared with saltpetre, especially in the old days of flint and steel. By removing the fungus and attending to the wound by cleaning away all dead and dying matter, and coating with tar, much benefit will ensue.

The =Leaf-shedding Fungus= or =Pine-leaf Scurf= (_Lophodermium pinastre_) is a well-known and widely distributed species, and is usually found on the Scotch and Austrian Pines. The leaves, when attacked, wither suddenly and fall off, the fungus being most prevalent after unusually dry weather, or in early spring succeeded by a frosty winter. It occurs both as a saprophyte on dead pine leaves and a parasite on the living foliage. We have been most successful in combating the attacks and preventing the spread of the pest by spraying the affected parts with “Bordeaux mixture.” Young trees under ten years of age are most commonly attacked, and when this occurs in the nursery borders, the plants should be rooted out and burned. On several Scottish and English estates, thousands of Scotch Pines have been killed out by the attacks of the leaf-shedding fungus.

One of the commonest fungi on old stumps is =Agaricus melleus=. It has no particular host, being found alike on coniferous and hard-wooded trees, and on both root and stem. Known as the honey fungus, and edible, this toadstool is about three inches in diameter, and of a yellowish-brown or rusty colour. It spreads with great rapidity both in the soil and between the bark and wood of the affected tree. The only remedy is digging out and destroying the fungus, and, in the case of healthy young trees, collecting and burning the mycelium.

Next to the larch canker, one of the most destructive diseases of forest trees is caused by attacks of the =Bladder-rust= or =Cluster-cup= (_Peridermium piniacicola_). It is a wound fungus and attacks almost every species of pine, the Scotch in particular, especially when the trees are growing on light, poor soils. Young trees up to, say, twenty years old are most commonly attacked by this fungus, which appears like blisters, emitting bright reddish-coloured spores. Rooting up and burning all affected trees is the best remedy.

[Illustration: POLYPORUS SULPHUREUS (ON WHITE POPLAR)]

_Polyporus sulphureus_ attacks many species of trees—yew, poplar, etc.