The Principles And Practice Of Spraying

The spraying of fruit trees in the United States is of comparatively

recent origin, having been a general commercial practice for less than

two decades. It involves the principle of applying with force and in

the form of a fine rain or mist, water in which a poison or a

substance which kills by contact is suspended. The first application

of the principle was against chewing insects with hellebore. Pure

arsenic was early used and soon led to the use of other arsenicals.



Our greatest fungicide, Bordeaux mixture, was discovered by accident

in 1882 when it was found to control mildew in France. Up until about

five years ago Bordeaux mixture as the fungicide and paris green as

the poison were almost universally used. Within the last few years,

however, there have been developed two substitutes which, although

known and used to some extent for twenty years, have only recently

come into such general use as practically to replace the old sprays.

These are lime and sulphur as the fungicide and partial insecticide

and arsenate of lead as a partial insecticide.



The necessity for and the advisability of spraying have already been

pointed out. There is an increasing demand for fine fruit the

supplying of which is possible only with thorough spraying. In the

humid East especially the competition of more progressive sections in

the West is demanding more and better spraying. There is no cure-all

in this process. It does not make a tree more fruitful except as it

improves its general health, but it does bring a larger percentage of

the fruit to perfection. Certain knowledge is fundamental; the grower

must know what he is spraying for, when and with what to combat it and

how to accomplish the desired result most effectively.



Spraying is an insurance against anticipated troubles with the fruit,

and the best and most successful growers are those most completely

insured. It has many general advantages also. It stimulates the grower

to a greater interest in his business because of the extra knowledge

and skill required. It compels thoroughness. It necessitates spending

money, therefore a return is looked for. To be sure, it is only one

of the operations necessary to success, but it enables us to grow a

quality of fruit which we could not obtain without it.



SPRAY MATERIALS are conveniently divided into two classes,

insecticides and fungicides. An insecticide is a poison by which the

insect is killed either directly by eating it, or indirectly by the

caustic, smothering, or stifling effects resulting from closing its

breathing pores. Direct poisons are used for insects which eat some

part of the tree or fruit and are called stomach poisons. Sprays which

kill indirectly are used for insects which suck the sap or juice from

the tree or fruit and are called contact sprays. Arsenical compounds

have supplanted practically all other substances used to combat

external biting insects. Two stomach poisons are commonly used,

namely, arsenate of lead and paris green, but the former is rapidly

replacing the latter.



ARSENATE OF LEAD is prepared by mixing three parts of crystallized

arsenate of soda with seven parts of crystallized white sugar

(acetate) of lead in water, but it will not as a rule pay the grower

to mix his own material, as arsenate of lead can be purchased in

convenient commercial form at a reasonable price. The preparation on

the market is a finely pulverized precipitate in two forms, one a

powder and the other a paste. These are probably about equally good

and are readily kept suspended in water. Less free arsenic is

contained in this form than in any other compound of arsenic, making

it safer to use, especially in heavy applications. Arsenate of lead

may be used without danger of burning the foliage as strong as five or

six pounds to fifty gallons of water, but three pounds is the usual

and a sufficient amount for the control of any apple insect for which

it is efficacious.



PARIS GREEN is being rapidly displaced by arsenate of lead for several

reasons. It is a compound of white arsenic, copper oxide, and acetic

acid. The commercial form is a crystal which in suspension settles

rapidly, a serious fault. It is more soluble than arsenate of lead and

hence there is greater danger of burning the foliage with it.

Moreover, it costs from twenty to twenty-five cents a pound, and the

arsenate of lead can be purchased for from eight to ten cents a pound.



The amount which it is safe to use in fifty gallons of water is from

one-half to three-quarters of a pound. When paris green is used alone

as a poison lime should be added. Both these arsenicals should be

thoroughly wet up by stirring in a smaller receptacle before they are

put into the spray tank, in order to get them in as complete

suspension as possible. They may be used in the same mixture with

Bordeaux or lime sulphur.