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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.



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