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Insects Affecting Shade and Forest Trees

Date Published: 
September, 1919
Original Author: 
J.S. Houser
Ohio Experiment Station
Original Publication: 
AACS Proceedings of the 33rd Annual Convention

The matter of insect control extends beyond the actual detecting and combating the specific pest at hand. Indeed, it should be one of the prime considerations in the planting of the tree itself, for some species of trees are much more susceptible to insect attack than others. Under the artificial conditions which many shade and ornamental trees are grown, it is essential that they be given every natural advantage possible, for without these natural advantages they are so greatly handicapped that they become an easy prey for insect hordes. After a careful study of planting, Dr. E. P. Felt of the New York State Museum has tabulated a list of these more common sorts arranged in accordance with their comparative freedom from insect injury. The list of trees together with the explanation of their arrangement is given in the following words from Dr. Felt:

The figure 3 has been placed opposite trees which are practically immune from insect injury; 2.5 indicate some damage. Trees having one somewhat serious enemy are rated at 2 and those having at least one notorious insect pest at 1.5. The species are arranged according to the comparative injury as follows:

Tree of Heaven 3 Catalpa 2
Ginkgo 3 European linden 1.5
Red Oak 2.5 American linden 1.5
Scarlet Oak 2.5 Horse chestnut 1.5
Oriental plane 2.5 Buckeye 1.5
American plane 2.5 Soft or silver maple 1.5
Tulip or tulip poplar 2.5 American elm 1.5
Sycamore maple 2 Hackberry 1.5
Sugar maple 2 Water or red elm 1.5
Norway maple 2 European elm 1
White maple 2 Scotch elm 1
Spruce 2 Cottonwood 5
White Oak 2 Carolina poplar 5
Burr Oak 2 Lombardy poplar 5
Red maple 2 Balm of gilead 5
Honey Locust 2 Yellow locust 5”

I do not wish to be understood, however, in saying that the preceding list should serve as the only guide in the selection of the trees for tree planting, since many other enter into one's consideration at that time. I merely wish it to serve as a guide for use from the standpoint of insect control other factors being equal.

Healthy, vigorous trees less liable to insect attack: It is a well known principle among both plants and animals that the weakling of the lot is more susceptible to attacks of diseases and predators than are healthy, vigorous specimens. For this reason one should be quite careful in the selection of the stock for planting. Overgrown nursery stock or planting stock taken from the woods where it may have stunned or where the opportunity to root development has not been what is should be, is quite likely to suffer severely from both insects and fungous diseases, particularly when first set. Such trees having been grown in shaded places are naturally quite subject to sunscald when set in the exposed open, and the cracked scalded areas on the trunk afford excellent points of entrance for boring larvae.

Allow space for development: Overcrowded plantings frequently make for a weakened condition among shade and ornamental trees. This is particularly likely to happen along streets where the residents plant excessive numbers of trees in order to make a show when the specimens are small. Later, as the trees grow, they hesitate to do the proper thing by way of pruning; thus we have crowded, unhealthy specimens. More over, the width of the tree belt is quite frequently wholly inadequate for the needs of the tree. Frequently we notice but a narrow strip of soil in which the trees are planted, and it is no wonder that when growing under such adverse conditions insect pests and fungous troubles find them highly susceptible hosts.

Avoid distributing the root system: Frequently trees are given an impetus toward susceptibility to insect depredations by having the root system disturbed through the lowering of the grade. Many of our most beautiful trees are highly susceptible to injury of this type since not a few of them are shallow rooting in habit when the surface of the roots is disturbed or injured, little remains to carry on the life work of the tree. Frequently the disturbing of the root system is avoided by the leaving of a mound of earth covering the roots, and if properly executed this does not prove an unsightly area. Where fills are made about trees, a well about trunk of the tree should be made of stone or bricks to retain the earth from falling about the tree trunk. The speaker has seen instances where fills of six feet have been made about trees and a well no more than six feet in diameter has saved the life of the specimen.

Protect trees in exposed areas: Insect pests and particularly trunk-boring species quite frequently make their entrance into the trunk of the tree through mechanical injuries to the bark. In street trees the most common source of these wounds is the mutilation of horses and of course with the rapid increase in the number of automobiles this menace is decreasing in corresponding measure. Nevertheless, it is still of sufficient importance to necessitate the protecting of trees grown in exposed situations, and for this purpose nothing more attractive nor efficacious has been found than the galvanized hardware cloth purchased in 15 inch rolls and of sufficient strength to make a rigid protector.

Electrical injuries: In a measure it may be said that electrical injuries aid and abet insect depredators. This, of course, does not hold true where the tree is killed outright by the current but it is highly applicable where only one or more limbs are injured or killed. This deadened portion of the tree then serves as an attractive bait for wood-boring insects which in time may spread to other parts of the tree.

Tree butchers: While he can not be classed as an insect pest, yet in the judgment of the speaker the tree butcher may rightly be considered one of our most destructive shade tree and ornamental pests. It is distressing to note the work of this class of men on fine specimens. Quite frequently trees that are a source of joy and pleasure to the neighborhood or passerby are butchered ruthlessly through mistaken ideas as to what tree trimming properly is. After some years of thought on the matter, it appeals to the speaker that we should have statutes limiting the practice of public pruners just as we have statutes limiting the practice of dentistry, veterinary medicine, materia medica, etc. The average householder is absolutely at the mercy of the public pruner and it seems to me that the owner of the tree deserves some sort of protection. He should have some way of assuring that the man who proposes to trim his trees is sufficiently trained to practice at least the principles of good tree husbandry, and it will not be long before the public demand for legislation on this point will be so great that it will be forthcoming. Such legislation would accomplish much toward doing away with the shyster practitioner just as our present excellent statutes make the practice of medical quackery highly undesirable and unprofitable.

Tree surgery: While the speaker feels rather strongly against the tree butcher, he has a very kindly feeling toward the expert tree surgeon. There is as great need for trained men to do public work in tree surgery, in the trimming of trees, the dressing of wounds, etc., as well as for public sprayers of trees. Some of the work done by the better class of tree surgeons is of most excellent character and it is a source of satisfaction to an owner who is able to restore a prized specimen on his premises after it appears that the days of the tree are numbered.

Insect pests: It is obviously impossible in the space allotted to this paper to give a detailed account of the various insect pests attacking shade and ornamental trees in the United States and Canada. Indeed, it would be almost prohibitive to attempt even to enumerate a list of these pests. A number of publications are available for this purpose in which the details of the life-history, development and control measures for the more important economic forms are considered. Just at this time there is being issued from the Ohio Station, Bulletin 332 which considers the problem in rather complete detail.

Spraying Machinery: In the successful control of the insects affecting shade and ornamental trees, one of the very necessary adjuncts is adequate preparation for spraying. The advance during the last ten years in the perfection of the spraying machinery has been little short of marvelous. During this period we have passed from the use of the common mist sprayer to what is known as the solid stream type of machine, a machine which by reason of its great capacity and the high pressure it is possible to develop with it, is able to throw the spraying liquid to a height of 100 feet, where the stream breaks into a fine mist and quickly and effectively covers the specimen under treatment. By the use of such machines the cost of spraying has been greatly decreased. It has been demonstrated in the East that 50 pounds of paste arsenate of lead dissolved in the proper amount of water and applied with one of these machines will yield almost perfect control of the gypsy and brown-tail moths. Such a performance is really little short of marvelous.

Spraying materials: Just a word about spraying material and I have finished. For most purposes, the cemetery superintendent will find three materials adequate for his needs. These are: (1) Arsenate of lead for chewing insects, ordinarily employed at the rate of 3 or 4 pounds of the paste form or 1½ to 2 pounds of the powder form to 50 gallons of water. It is applied as soon as the depredators are noticed to be at work since younger insects always are less difficult to destroy than they are when they become older and consequently more rugged. (2) Miscible oil used against scale insects and red spider in the spring before the leaves appear. It is employed at the rate of 1 gallon to 15 gallons of water. Since this material kills by contact, exceptional care should be exercised in making the work of application thorough. (3) Nicotine sulfate, used against plant lice and similar soft-bodied sucking insects during the summer months when the foliage is out. Usually this material is used at the rate of 1 part to 50 parts of water with enough soap added to make suds. The amount of soap varies according to the degree of hardness of the water but ordinarily 2 pounds to 50 gallons of the diluted nicotine sulfate is adequate.

From the publication:
“AACS - Proceedings of the 33rd Annual Convention held at Cincinnati, OH"
September 24, 25 and 26, 1919