Studies of Trees Part 16

THE CARE OF TREES

STUDY I. INSECTS INJURIOUS TO TREES AND HOW TO COMBAT THEM

In a general way, trees are attacked by three cla.s.ses of insects, and the remedy to be employed in each case depends upon the cla.s.s to which the insect belongs. The three cla.s.ses of insects are:

1. Those that *chew* and swallow some portion of the leaf; as, for example, the elm leaf beetle, and the tussock, gipsy, and brown-tail moths.

2. Those that *suck* the plant juices from the leaf or bark; such as the San Jose scale, oyster-sh.e.l.l, and scurfy scales, the cottony maple scale, the maple phenacoccus on the sugar maples, and the various aphides on beech, Norway maple, etc.

3. Those that *bore* inside of the wood or inner bark. The princ.i.p.al members of this cla.s.s are the leopard moth, the hickory-bark borer, the sugar-maple borer, the elm borer, and the bronze-birch borer.

The chewing insects are destroyed by spraying the leaves with a.r.s.enate of lead or Paris green. The insects feed upon the poisoned foliage and thus are themselves poisoned.

The sucking insects are killed by a contact poison: that is, by spraying or washing the affected parts of the tree with a solution which acts externally on the bodies of the insects, smothering or stifling them.

The standard solutions for this purpose are kerosene emulsion, soap and water, tobacco extract, or lime-sulfur wash.

[Ill.u.s.tration: FIG. 97.--A Gas-power Spraying Apparatus.]

The boring insects are eliminated by cutting out the insect with a knife, by injecting carbon bisulphide into the burrow and clogging the orifice immediately after injection with putty or soap, or in some cases where the tree is hopelessly infested, by cutting down and burning the entire tree.

[Ill.u.s.tration: FIG. 98.--A Barrel Hand-pump Spraying Outfit.]

For information regarding the one of these three cla.s.ses to which any particular insect belongs, and for specific instructions on the application of a remedy, the reader is advised to write to his State Entomologist or to the U.S. Bureau of Entomology at Washington, D.C. The letter should state the name of the tree affected, together with the character of the injury, and should be accompanied by a specimen of the insect, or by a piece of the affected leaf or bark, preferably by both.

The advice received will be authentic and will be given without charge.

[Ill.u.s.tration: FIG. 99.--Egg-ma.s.ses of the Tussock Moth.]

When to spray: _In the case of chewing insects_, the latter part of May is the time to spray. The caterpillars hatch from their eggs, and the elm leaf beetle leaves its winter quarters at that time. _In the case of sucking insects_, the instructions will have to be more specific, depending upon the particular insect in question. Some sucking insects can best be handled in May or early June when their young emerge, others can be effectively treated in the fall or winter when the trees are dormant.

How to spray: Thoroughness is the essential principle in all spraying.

In the case of leaf-eating insects, this means covering every leaf with the poison and applying it to the under side of the leaves, where the insects generally feed. In the case of sucking insects, thoroughness means an effort to touch every insect with the spray.

It should be borne in mind that the insect can be killed only when hit with the chemical. The solution should be well stirred, and should be applied by means of a nozzle that will coat every leaf with a fine, mist-like spray. Mere drenching or too prolonged an application will cause the solution to run off. Special precautions should be taken with contact poisons to see that the formula is correct. Too strong a solution will burn the foliage and tender bark.

Spraying apparatus: There are various forms of spraying apparatus in the market, including small knapsack pumps, barrel hand-pumps, and gasolene and gas-power sprayers, Figs. 97 and 98. Hose and nozzles are essential accessories. One-half inch, three-ply hose of the best quality is necessary to stand the heavy pressure and wear. Two 50-foot lengths is the usual quant.i.ty required for use with a barrel hand-pump. Each line of hose should be supplied with a bamboo pole 10 feet long, having a bra.s.s tube pa.s.sed through it to carry the nozzle. The Vermorel nozzle is the best type to use. The cost of a barrel outfit, including two lines of hose, nozzles and truck, should be from $30 to $40. Power sprayers cost from $150 to $300 or more.

Spraying material: _a.r.s.enate of lead_ should be used in the proportion Of 4 pounds of the chemical to 50 gallons of water. A brand of a.r.s.enate of lead containing at least 14 per cent of a.r.s.enic oxide with not more than 50 per cent of water should be insisted upon. This spray may be used successfully against caterpillars and other leaf-eating insects in the spring or summer.

_Whale-oil soap_ should be used at the rate of 1 pounds of the soap to 1 gallon of hot water, if applied to the tree in winter. As a spray in summer, use 1 pound of the soap to 5 gallons of water. This treatment is useful for most sucking insects.

_Lime-sulfur wash_ is an excellent material to use against sucking insects, such as the San Jose scale and other armored scales. The application of a lime-sulfur wash when put on during the dormant season is not likely to harm a tree and has such an excellent cleansing effect that the benefits to be derived in this direction alone are often sufficient to meet the cost of the treatment.

Lime-sulfur wash consists of a mixture, boiled one hour, of 40 pounds of lime and 80 pounds of sulfur, in 50 gallons of water. It may be had in prepared form and should then be used at the rate of 1 gallon to about 9 gallons of water in winter or early spring before the buds open. At other times of the year and for the softer-bodied insects a more diluted mixture, possibly 1 part to 30 or 40 parts of water, should be used, varying with each case separately.

_Kerosene emulsion_ consists of one-half pound of hard soap, 1 gallon of boiling water, and 2 gallons of kerosene. It may be obtained in prepared form and is then to be used at the rate of one part of the solution to nine parts of water when applied in winter or to the bark only in summer. Use 2 gallons of the solution to a 40-gallon barrel of water when applying it to the leaves in the summer.

Kerosene emulsion is useful as a treatment for scale insects.

_Tobacco water_ should be prepared by steeping one-half pound of tobacco stems or leaves in a gallon of boiling water and later diluting the product with 5 to 10 gallons of water. It is particularly useful for plant lice in the summer.

The life history of an insect: In a general way, all insects have four stages of transformation before a new generation is produced. It is important to consider the nature of these four stages in order that the habits of any particular insect and the remedies applicable in combating it may be understood.

All insects develop from _eggs_, Fig. 99. The eggs then hatch into caterpillars or grubs, which is the _larva_ stage, in which most insects do the greatest damage to trees. The caterpillars or grubs grow and develop rapidly, and hence their feeding is most ravenous.

Following the larva stage comes the third or _pupa_ stage, which is the dormant stage of the insect. In this stage the insect curls itself up under the protection of a silken coc.o.o.n like the tussock moth, or of a curled leaf like the brown-tail moth, or it may be entirely unsheltered like the pupa of the elm leaf beetle. After the pupa stage comes the _adult insect_, which may be a moth or a beetle.

A study of the four stages of any particular insect is known as a study of its _life history_. The important facts to know about the life history of an insect are the stage in which it does most of its feeding, and the period of the year in which this occurs. It is also important to know how the insect spends the winter in order to decide upon a winter treatment.

IMPORTANT INSECTS

THE ELM LEAF BEETLE

Life history: The elm leaf beetle, Fig. 100, is annually causing the defoliation of thousands of elm trees throughout the United States.

Several successive defoliations are liable to kill a tree. The insects pa.s.s the winter in the beetle form, hiding themselves in attics and wherever else they can secure shelter. In the middle of May when the buds of the elm trees unfold, the beetles emerge from their winter quarters, mate, and commence eating the leaves, thus producing little holes through them. While this feeding is going on, the females deposit little, bright yellow eggs on the under side of the leaves, which soon hatch into small larvae or grubs. The grubs then eat away the soft portion of the leaf, causing it to look like lacework. The grubs become full grown in twenty days, crawl down to the base of the tree, and there transform into naked, orange-colored pupae. This occurs in the early part of August. After remaining in the pupa stage about a week, they change into beetles again, which either begin feeding or go to winter quarters.

Remedies: There are three ways of combating this insect: First, by _spraying the foliage_ with a.r.s.enate of lead in the latter part of May while the beetles are feeding, and repeating the spraying in June when the larvae emerge. The spraying method is the one most to be relied on in fighting this insect. A second, though less important remedy, consists in _destroying the pupae_ when they gather in large quant.i.ties at the base of the tree. This may be accomplished by gathering them bodily and destroying them, or by pouring hot water or a solution of kerosene over them. In large trees it may be necessary to climb to the crotches of the main limbs to get some of them. The third remedy lies in gathering and _destroying the adult beetles_ when found in their winter quarters.

The application of bands of burlap or "tanglefoot," or of other substances often seen on the trunks of elm trees is useless, since these bands only prevent the larvae from crawling down from the leaves to the base and serve to prevent nothing from crawling up.

Sc.r.a.ping the trunks of elm trees is also a waste of effort.

[Ill.u.s.tration: FIG. 100.--The Elm Leaf Beetle. (After Dr. E.P. Felt.)

1. Egg cl.u.s.ter, enlarged. 1a. Single egg, greatly enlarged. 2. Young larva, enlarged. 3. Full grown larva, much enlarged. 4. Pupa, enlarged.

5. Overwintered beetle, enlarged. 6. Fresh, brightly colored beetle, enlarged. 7. Under surface of leaf showing larvae feeding. 8. Leaf eaten by larvae. 9. Leaf showing holes eaten by beetles.]

THE TUSSOCK MOTH

Life history: This insect appears in the form of a red-headed, yellow-colored caterpillar during the latter part of May, and in June and July. The caterpillars surround themselves with silken coc.o.o.ns and change into pupae. The mature moths emerge from the coc.o.o.ns after a period of about two weeks, and the females, which are wingless, soon deposit their eggs on the bark of trees, on twigs, fences, and other neighboring objects. These eggs form white cl.u.s.ters of nearly 350 individual eggs each, and are very conspicuous all winter, see Fig. 101.

Remedies: There are two ways of combating this insect: (1) By spraying with a.r.s.enate of lead for the caterpillars during the latter part of May and early June. (2) By removing and destroying the egg ma.s.ses in the fall or winter.

[Ill.u.s.tration: FIG. 101.--The Tussock Moth. (After Dr. E.P. Felt.)

1. Caterpillar. 2. Male moth. 3. Female moth laying eggs. 4 Coc.o.o.ns. 5.

Cast skins of caterpillar. 6. Work of young caterpillar. 7. Male pupa. 8 and 9. Girdled branches.]

THE GIPSY MOTH

Life history: This insect, imported from Europe to this country in 1868, has ever since proved a serious enemy of most shade, forest, and fruit trees in the New England States. It even feeds on evergreens, killing the trees by a single defoliation.

The insect appears in the caterpillar stage from April to July. It feeds at night and rests by day. The mature caterpillar, which is dark in color, may be recognized by rows of blue and red spots along its back. After July, egg ma.s.ses are deposited by the female moths on the bark of trees, and on leaves, fences, and other neighboring objects. Here they remain over the winter until they hatch in the spring. The flat egg ma.s.ses are round or oval in shape, and are yellowish-brown in color. See Fig. 102.

Remedies: Spray for the caterpillars in June with a.r.s.enate of lead and apply creosote to the egg ma.s.ses whenever found.

THE BROWN-TAIL MOTH

Life history: This insect was introduced here from Europe in 1890 and has since done serious damage to shade, forest, and fruit trees, and to shrubs in the New England States.