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 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;