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.