The two classes of insecticides are here described, - the poisons (arsenicals and white hellebore) for chewing insects, as the beetles and all kinds of worms; the contact insecticides, as kerosene, oils, soap, tobacco, lime-sulfur, for plant-lice, scale, and insects in such position that the material cannot be fed to them (as maggots in the underground parts).

Paris Green

The standard insecticidal poison. This is used in varying strengths, depending on the insect to be controlled and the kind of plant treated. Mix the Paris green into a paste and then add to the water. Keep the mixture thoroughly agitated while spraying. If for use on fruit trees, add 1 lb. of quick lime for every pound of Paris green to prevent burning the foliage. For potatoes it is frequently used alone, but it is much safer to use the lime. Paris green and bordeaux mixture may be combined without lessening the value of either, and the caustic action of the arsenic is prevented. The proportion of the poison to use is given under the various insects discussed in the succeeding pages.

Arsenate Of Lead

This can be applied in a stronger mixture than other arsenical poisons without injuring the foliage. It is, therefore, much used against beetles and other insects that are hard to poison, as elm-leaf beetle and canker-worm. It comes as a paste or a powder, and should be mixed thoroughly with a small quantity of water before placing in the sprayer, else the nozzles will clog. Arsenate of lead and bordeaux mixture or lime-sulfur can be combined without lessening the value of either. It is used in strengths varying from 4 to 10 lb. per 100 gal., depending on the kind of insect to be killed.

Arsenite of soda and arsenite of lime are sometimes used with bordeaux mixture.

White Hellebore

For wet application, use fresh white hellebore, 4 oz.; water, 2 or 3 gal. For dry application, use hellebore, 1 lb.; flour or air-slaked lime, 5 lb. This is a yellowish white powder made from the roots of the white hellebore plant. It loses its strength after a time and should be used fresh. It is used as a substitute for the arsenical poisons on plants or fruits soon to be eaten, as on currants and gooseberries for the currant-worm.

Tobacco

This is a valuable insecticide and is used in several forms. As a dust it is used extensively in greenhouses for plant-lice, and in nurseries and about apple trees for the woolly aphis. Tobacco decoction is made by steeping or soaking the stems in water. It is often used as a spray against plant-lice. Tobacco in the form of extracts, punks, and powders is sold under various trade names for use in fumigating greenhouses. (See page 188).

Kerosene Emulsion

Hard, soft, or whale-oil soap, J lb.; water, 1 gal.; kerosene, 2 gal. Dissolve the soap in hot water; remove from the fire and while still hot add the kerosene. Pump the liquid back into itself for five or ten minutes or until it becomes a creamy mass. If properly made, the oil will not separate out on cooling.

For use on dormant trees, dilute with 5 to 7 parts of water. For killing plant-lice on foliage dilute with 10 to 15 parts of water. Crude oil emulsion is made in the same way by substituting crude oil in place of kerosene. The strength of oil emulsions is frequently indicated by the percentage of oil in the diluted liquid: -

For a 10% emulsion add 17 gal. of water to 3 gal. stock emulsion. For a 15% emulsion add 10½ gal. of water to 3 gal. stock emulsion. For a 20% emulsion add 7 gal. of water to 3 gal. stock emulsion. For a 25% emulsion add 5 gal. of water to 3 gal. stock emulsion.

Carbolic Acid Emulsion

Soap, 1 lb.; water, 1 gal.; crude carbolic acid, 1 pt. Dissolve the soap in hot water, add the carbolic acid, and agitate into an emulsion. For use against root-maggots, dilute with 30 parts of water.

Soaps

An effective insecticide for plant-lice is whale-oil soap. Dissolve in hot water and dilute so as to obtain one pound of soap to every five or seven gallons of water. This strength is effective against plant-lice. It should be applied in stronger solutions, however, for scale insects. Home-made soaps and good laundry soaps, like Ivory soap, are often as effective as whale-oil soap.

Miscible Oils

There are now on the market a number of preparations of petroleum and other oils intended primarily for use against the San Jose* scale. They mix readily with cold water and are immediately ready for use. While quickly prepared, easily applied, and generally effective, they cost considerably more than lime-sulfur wash. They are, however, less corrosive to the pumps and more agreeable to use. They are especially valuable to the man with only a few trees or shrubs who would not care to go to the trouble and expense to make up the lime-sulfur wash. They should be diluted with not more than 10 or 12 parts of water. Use only on dormant trees.

Lime And Sulfur Wash

Quicklime, 20 lb.; flowers of sulfur, 15 lb.; water, 50 gal. The lime and sulfur must be thoroughly boiled. An iron kettle is often convenient for the work. Proceed as follows: Place the lime in the kettle. Add hot water gradually in sufficient quantity to produce the most rapid slaking of the lime. When the lime begins to slake, add the sulfur and stir together. If convenient, keep the mixture covered with burlap to save the heat. After slaking has ceased, add more water and boil the mixture one hour. As the sulfur goes into solution, a rich orange-red or dark green color will appear. After boiling sufficiently, add water to the required amount and strain into the spray tank. The wash is most effective when applied warm, but may be applied cold. If one has access to a steam boiler, boiling with steam is more convenient and satisfactory. Barrels may be used for holding the mixture, and the steam applied by running a pipe or rubber hose into the mixture. Proceed in the same way until the lime is slaked, when the steam may be turned on.

Continue boiling for 45 min. to an hour, or until sulfur is dissolved.

This strength can be applied safely only when the trees are dormant. It has been mainly an insecticide for use on San Jose scale, for which it affords a standard treatment; but recently it has been modified for use against other insects and certain fungi (as peach leaf-curl, apple-scab, brown-rot).

Four kinds of lime-sulfur preparation are now recognized: (1) the ordinary home made wash for winter use (given above); (2) concentrated commercial solutions, now on the market under various names; (3) home-made concentrated solution; (4) self-boiled lime-sulfur. The commercial concentrates differ much in strength; and these, as well as the home-made concentrate, should be tested by a hydrometer before use, and then they should be diluted with water to a definite strength. The formulas for these washes are discussed on pages 539-541.