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.

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.

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.

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 quantity required for use with a barrel

hand-pump. Each line of hose should be supplied with a bamboo pole

10 feet long, having a brass tube passed 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 $30 or

more.

Spraying material:

_Arsenate of lead_ should be used in the proportion Of 4 pounds of the

chemical to 50 gallons of water. A brand of arsenate of lead

containing at least 14 per cent of arsenic 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 11/2 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 cocoon 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.

Tree Studies

How To Identify Trees
Group I The Pines
The White Pine (pinus Strobus)
The Pitch Pine (pinus Rigida)
The Scotch Pine (pinus Sylvestris)
Group Ii The Spruce And Hemlock
The Norway Spruce (picea Excelsa)
Hemlock (tsuga Canadensis)
Group Iii The Red Cedar And Arbor-vitae
Red Cedar (juniperus Virginiana)
Arbor-vitae; Northern White Cedar (thuja Occidentalis)
Group Iv The Larch And Cypress
The European Larch (larix Europaea)
Bald Cypress (taxodium Distichum)
Group V The Horsechestnut, Ash And Maple
The Horsechestnut
The White Ash (fraxinus Americana)
Sugar Maple (acer Saccharum)
Silver Maple (acer Saccharinum)
Red Maple (acer Rubrum)
Norway Maple (acer Platanoides)
Box Elder (acer Negundo)
Group Vi Trees Told By Their Form: Elm, Poplar, Gingko And Willow
American Elm (ulmus Americana)
Lombardy Or Italian Poplar (populus Nigra, Var Italica)
Gingko Or Maidenhair Tree (gingko Biloba)
Weeping Willow (salix Babylonica)
Group Vii Trees Told By Their Bark Or Trunk: Sycamore, Birch, Beech,
Blue Beech, Ironwood, And Hackberry
The Sycamore Or Plane Tree (platanus Occidentalis)
Gray Or White Birch (betula Populifolia)
American Beech (fagus Americana)
Blue Beech Or Hornbeam (carpinus Caroliniana)
Hackberry (celtis Occidentalis)
Group Viii The Oaks And Chestnut
White Oak (quercus Alba)
Black Oak (quercus Velutina)
Red Oak (quercus Rubra)
Pin Oak (quercus Palustris)
Chestnut (castanea Dentata)
Group Ix The Hickories, Walnut And Butternut
Shagbark Hickory (hicoria Ovata)
Mockernut Hickory (hicoria Alba)
Black Walnut (juglans Nigra)
Group X Tulip Tree, Sweet Gum, Linden, Magnolia, Locust, Catalpa,
Dogwood, Mulberry And Osage Orange
Tulip Tree (liriodendron Tulipifera)
Sweet Gum (liquidambar Styraciflua)
American Linden (tilia Americana)
The Magnolias