Study Ii Tree Diseases
Because trees have wants analogous to those of human beings, they also
have diseases similar to those which afflict human beings. In many cases
these diseases act like cancerous growths upon the human body; in some
instances the ailment may be a general failing due to improper feeding,
and in other cases it may be due to interference with the life processes
of the tree.
How to tell an ailing tree: Whatever the cause, an ailing tree will
manifest its ailment by one or more symptoms.
A change of color in the leaves at a time when they should be
perfectly green indicates that the tree is not growing under normal
conditions, possibly because of an insufficiency of moisture or
light or an overdose of foreign gases or salts. Withering of the
leaves is another sign of irregularity in water supply. Dead tops
point to some difficulty in the soil conditions or to some disease
of the roots or branches. Spotted leaves and mushroom-like growths
or brackets protruding from the bark as in Fig. 108, are sure signs
of disease.
In attempting to find out whether a tree is healthy or not, one
would therefore do well to consider whether the conditions under
which it is growing are normal or not; whether the tree is suitable
for the location; whether the soil is too dry or too wet; whether
the roots are deprived of their necessary water and air by an
impenetrable cover of concrete or soil; whether the soil is well
drained and free from foreign gases and salts; whether the tree is
receiving plenty of light or is too much exposed; and whether it is
free from insects and fungi.
If, after a thorough examination, it is found that the ailment has
gone too far, it may not be wise to try to save the tree. A timely
removal of a tree badly infested with insects or fungi may often be
the best procedure and may save many neighboring trees from
contagious infection. For this, however, no rules can be laid down
and much will depend on the local conditions and the judgment and
knowledge of the person concerned.
Fungi as factors of disease: The trees, the shrubs and the flowers with
which we are familiar are rooted in the ground and derive their food
both from the soil and from the air. There is, however, another
group of plants,--_the fungi_,--the roots of which grow in trees and
other plants and which obtain their food entirely from the trees or
plants upon which they grow. The fungi cannot manufacture their own
food as other plants do and consequently absorb the food of their
host, eventually reducing it to dust. The fungi are thus
disease-producing factors and the source of most of the diseases of
trees.
When we can see fungi growing on a tree we may safely assume that
they are already in an advanced state of development. We generally
discover their presence when their fruiting bodies appear on the
surface of the tree as shown in Fig 109. These fruiting bodies are
the familiar mushrooms, puffballs, toadstools or shelf-like brackets
that one often sees on trees. In some cases they spread over the
surface of the wood in thin patches. They vary in size from large
bodies to mere pustules barely visible to the naked eye. Their
variation in color is also significant, ranging from colorless to
black and red but never green. They often emulate the color of the
bark, Fig. 110.
Radiating from these fruiting bodies into the tissues of the tree
are a large number of minute fibers, comprising the _mycelium_ of
the fungus. These fibers penetrate the body of the tree in all
directions and absorb its food. The mycelium is the most important
part of the fungous growth. If the fruiting body is removed, another
soon takes its place, but if the entire mycelium is cut out, the
fungus will never come back. The fruiting body of the fungus bears
the seed or _spores_. These spores are carried by the wind or
insects to other trees where they take root in some wound or crevice
of the bark and start a new infestation.
The infestation will be favored in its growth if the spore can find
plenty of food, water, warmth and darkness. As these conditions
generally exist in wounds and cavities of trees, it is wise to keep
all wounds well covered with coal tar and to so drain the cavities
that moisture cannot lodge in them. This subject will be gone into
more fully in the following two studies on "Pruning Trees" and "Tree
Repair."
While the majority of the fungi grow on the trunks and limbs of
trees, some attack the leaves, some the twigs and others the roots.
Some fungi grow on living wood some on dead wood and some on both.
Those that attack the living trees are the most dangerous from the
standpoint of disease.
The chestnut disease: The disease which is threatening the destruction
of all the chestnut trees in America is a fungus which has, within
recent years, assumed such vast proportions that it deserves special
comment. The fungus is known as _Diaporthe parasitica_ (Murrill),
and was first observed in the vicinity of New York in 1905. At that
time only a few trees were known to have been killed by this
disease, but now the disease has advanced over the whole chestnut
area in the United States, reaching as far south as Virginia and as
far west as Buffalo. Fig. 111 shows the result of the chestnut
disease.
The fungus attacks the cambium tissue underneath the bark. It enters
through a wound in the bark and sends its fungous threads from the
point of infection all around the trunk until the latter is girdled
and killed. This may all happen within one season. It is not until
the tree has practically been destroyed that the disease makes its
appearance on the surface of the bark in the form of brown patches
studded with little pustules that carry the spores. When once
girdled, the tree is killed above the point of infection and
everything above dies, while some of the twigs below may live until
they are attacked individually by the disease or until the trunk
below their origin is infected.
All species of chestnut trees are subject to the disease. The
Japanese and Spanish varieties appear to be highly resistant, but
are not immune. Other species of trees besides chestnuts are not
subject to the disease.
There is no remedy or preventive for this disease. From the nature
of its attack, which is on the inner layer of the tree, it is
evident that all applications of fungicides, which must necessarily
be applied to the outside of the tree, will not reach the disease.
Injections are impossible and other suggested remedies, such as
boring holes in the wood for the purpose of inserting chemicals, are
futile.
The wood of the chestnut tree, within three or four years after its
death, is still sound and may be used for telephone and telegraph
poles, posts, railroad ties, lumber and firewood.
Spraying for fungous diseases: Where a fungous disease is attacking the
leaves, fruit, or twigs, spraying with Bordeaux mixture may prove
effective. The application of Bordeaux mixture is deterrent rather
than remedial, and should therefore be made immediately before the
disease appears. The nature of the disease and the time of treatment
can be determined without cost, by submitting specimens of affected
portions of the plant for analysis and advice to the State
Agricultural Experiment Station or to the United States Department
of Agriculture.
Bordeaux mixture, the standard fungicide material, consists of a
solution of 6 pounds of copper sulphate (blue vitriol) with 4 pounds
of slaked lime in 50 gallons of water. It may be purchased in
prepared form in the open market, and when properly made, has a
brilliant sky-blue color. Spraying with Bordeaux mixture should be
done in the fall, early spring, or early summer, but never during
the period when the trees are in bloom.
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Tree Studies
How To Identify Trees
Group I The Pines
The White Pine (pinus Strobus)
The Pitch Pine (pinus Rigida)
The Scotch Pine (pinus Sylvestris)
Group Ii The Spruce And Hemlock
The Norway Spruce (picea Excelsa)
Hemlock (tsuga Canadensis)
Group Iii The Red Cedar And Arbor-vitae
Red Cedar (juniperus Virginiana)
Arbor-vitae; Northern White Cedar (thuja Occidentalis)
Group Iv The Larch And Cypress
The European Larch (larix Europaea)
Bald Cypress (taxodium Distichum)
Group V The Horsechestnut, Ash And Maple
The Horsechestnut
The White Ash (fraxinus Americana)
Sugar Maple (acer Saccharum)
Silver Maple (acer Saccharinum)
Red Maple (acer Rubrum)
Norway Maple (acer Platanoides)
Box Elder (acer Negundo)
Group Vi Trees Told By Their Form: Elm, Poplar, Gingko And Willow
American Elm (ulmus Americana)
Lombardy Or Italian Poplar (populus Nigra, Var Italica)
Gingko Or Maidenhair Tree (gingko Biloba)
Weeping Willow (salix Babylonica)
Group Vii Trees Told By Their Bark Or Trunk: Sycamore, Birch, Beech,
Blue Beech, Ironwood, And Hackberry
The Sycamore Or Plane Tree (platanus Occidentalis)
Gray Or White Birch (betula Populifolia)
American Beech (fagus Americana)
Blue Beech Or Hornbeam (carpinus Caroliniana)
Hackberry (celtis Occidentalis)
Group Viii The Oaks And Chestnut
White Oak (quercus Alba)
Black Oak (quercus Velutina)
Red Oak (quercus Rubra)
Pin Oak (quercus Palustris)
Chestnut (castanea Dentata)
Group Ix The Hickories, Walnut And Butternut
Shagbark Hickory (hicoria Ovata)
Mockernut Hickory (hicoria Alba)
Black Walnut (juglans Nigra)
Group X Tulip Tree, Sweet Gum, Linden, Magnolia, Locust, Catalpa,
Dogwood, Mulberry And Osage Orange
Tulip Tree (liriodendron Tulipifera)
Sweet Gum (liquidambar Styraciflua)
American Linden (tilia Americana)
The Magnolias
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Informational