Studies of Trees Part 17

It appears in the caterpillar stage in the early spring and continues to feed on the leaves and buds until the last of June.

Then the caterpillars pupate, the moths come out, and in July and August the egg cl.u.s.ters appear. These hatch into caterpillars which form nests for themselves by drawing the leaves together. Here they remain protected until the spring. See Fig. 103.

Remedies: Collect the winter nests from October to April and burn them.

Also spray the trees for caterpillars in early May and especially in August with a.r.s.enate of lead.

[Ill.u.s.tration: FIG. 102.--The Gipsy Moth. (After F.W. Rane Ma.s.s. State Forester.)]

[Ill.u.s.tration: FIG. 103.--The Brown-tail Moth. (After F.W. Rane, Ma.s.s.

State Forester.)]

[Ill.u.s.tration: FIG. 104.--Larva of the Leopard Moth.]

THE FALL WEBWORM

The caterpillars of this insect congregate in colonies and surround themselves with a web which often reaches the size of a foot or more in diameter. These webs are common on trees in July and August. Cutting off the webs or burning them on the twigs is the most practical remedy.

[Ill.u.s.tration: FIG. 105.--Branch Showing Work of the Leopard Moth Larva.]

THE LEOPARD MOTH

Life history: This insect does its serious damage in the grub form. The grubs which are whitish in color with brown heads, and which vary in size from 3/8 of an inch to 3 inches in length (Fig. 104), may be found boring in the wood of the branches and trunk of the tree all winter. Fig. 105. The leopard moth requires two years to complete its round of life. The mature moths are marked with dark spots resembling a leopard's skin, hence the name. Fig. 106. It is one of the commonest and most destructive insects in the East and is responsible for the recent death of thousands of the famous elm trees in New Haven and Boston. Fig. 107.

[Ill.u.s.tration: FIG. 106.--The Leopard Moth.]

Remedies: Trees likely to be infested with this insect should be examined three or four times a year for wilted twigs, dead branches, and strings of expelled fra.s.s; all of which may indicate the presence of this borer. Badly infested branches should be cut off and burned. Trees so badly infested that treatment becomes too complicated should be cut down and destroyed. Where the insects are few and can be readily reached, an injection of carbon bisulphide into the burrow, the orifice of which is then immediately closed with soap or putty, will often destroy the insects within.

[Ill.u.s.tration: FIG. 107.--Elm Tree Attacked by the Leopard Moth.]

THE HICKORY BARK BORER

Life history: This insect is a small brown or black beetle in its mature form and a small legless white grub in its winter stage. The beetles appear from June to August. In July they deposit their eggs in the outer sapwood, immediately under the bark of the trunk and larger branches. The eggs soon hatch and the grubs feed on the living tissue of the tree, forming numerous galleries. The grubs pa.s.s the winter in a nearly full-grown condition, transform to pupae in May, and emerge as beetles in June.

Remedies: The presence of the insect can be detected by the small holes in the bark of the trees and the fine sawdust which is ejected from these holes, when the insects are active. It is important to emphasize the advisability of detecting the fine sawdust because that is the best indication of the actual operations of the hickory bark borer. These holes, however, will not be noticeable until the insect has completed its transformation. In summer, the infested trees show wilted leaves and many dead twigs. Holes in the base of the petioles of these leaves are also signs of the working of the insect. Since the insect works underneath the bark, it is inaccessible for treatment and all infested trees should be cut down and burned, or the bark removed and the insects destroyed. This should be done before the beetles emerge from the tree in June.

PLANT LICE OR APHIDES

These often appear on the under side of the leaves of the beech, Norway maple, tulip tree, etc. They excrete a sweet, sticky liquid called "honey-dew," and cause the leaves to curl or drop. Spraying with whale-oil soap solution formed by adding one pound of the soap to five gallons of water is the remedy.

STUDY II. TREE DISEASES

Because trees have wants a.n.a.logous 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.

[Ill.u.s.tration: FIG. 108.--A Bracket Fungus (_Elfvingia megaloma_) on a Tulip Tree.]

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 a.s.sume 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, puffb.a.l.l.s, 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.

[Ill.u.s.tration: FIG. 109.--The Fruiting Body of a Fungus.]

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."

[Ill.u.s.tration: FIG. 110.--The Birch-fungus rot. (_Polyponis betulinus_ Fr.) Note the similarity in the color of the fruiting body and bark of the tree.]

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, a.s.sumed 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 j.a.panese and Spanish varieties appear to be highly resistant, but are not immune. Other species of trees besides chestnuts are not subject to the disease.

[Ill.u.s.tration: FIG. 111.--Chestnut Trees Killed by the Chestnut 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 a.n.a.lysis 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.

STUDY III. PRUNING TREES

FUNDAMENTAL PRINCIPLES