THE CARE OF TREES

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

In a general way, trees are attacked by three classes of insects, and the remedy to be employed in each case depends upon the class to which the insect belongs.  The three classes 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-shell, 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 principal members of this class 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 arsenate 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.

[Illustration:  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.

[Illustration:  FIG. 98.—­A Barrel Hand-pump Spraying Outfit.]

For information regarding the one of these three classes 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.

[Illustration:  FIG. 99.—­Egg-masses 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.