Bearing in mind what has been said just now of the want of certainty in any remedy whatsoever, the tree-grower who follows these directions will most likely find his work successful and his deciduous plants cleaned of "scale" on the bark.
A second method may be adopted—namely, the painting-over of the trunk and branches, without attempting to forcibly detach any "scales" with the brush. This, properly performed and with proper fluids, is likely to be just as efficacious as the other, for the fluid should "run in" under the scales, surround the eggs, and prevent them from hatching. It gives less trouble than the hard brushing, and is equally destructive to the Coccids. It has, however, of course, not the same cleaning effect upon fungoid growths or incrustations impeding the free "respiration" of the plant.
For deciduous trees, then, such as apple- or pear-trees in an orchard, the simple remedy is severe pruning at the dead of winter, and the coating of the trees with a destructive fluid, laid on with a brush on every part, preferably with a hard brush vigorously used, but leaving a thin coat of the fluid on the bark.
It must be thoroughly understood that, a week or two after the first application, the "scales" left on the tree should be examined, and, if the eggs are not killed, a second coating of the fluid should be applied.
The treatment of evergreen plants, or of plants which are attacked both on the bark and leaves, is really the same as the above as regards its object, but it necessarily differs in its method. Here, again, it is desired not only to kill the insects themselves, but also to devitalize the eggs; but in this case the work is much harder, for the eggs are especially difficult to reach. Still, there is this advantage: that in dealing with evergreens the season of the year need not be specially studied, and, in default of touching the eggs, one may get at the young larvæ. The remedy is again a fluid, but it must be applied in the form of spray. Coccids are sometimes found on the upper surfaces of leaves, but as a rule they affect the lower sides. This, of course, renders it much more difficult to get at them; and the ordinary rose of a garden syringe would not, as a general thing, distribute the fluid in a sufficiently-fine form. The finer the spray and the more it is forced into every corner and nook of the plant the better. Various force-pumps and spray-throwers have been invented for this purpose in the United States; but probably tree-growers in this country need only procure the finest possible rose for their syringes, and use them in the ordinary way. The fluid should be thrown as thoroughly as possible on all parts of the plant, every care being taken to direct it most fully against the under sides of the leaves.
The work, then, to be done is in itself simple enough. A destructive fluid must be selected and applied according to the character of the insect and its position on the tree. For covered or naked insects on the bark, apply it with a hard, stiff brush; for covered or naked insects on the leaves, apply it in the form of the finest spray thoroughly forced as much as possible into every nook and cranny, and especially against the under side of the leaves.
The question, "What is the best fluid to use?" is more complicated. Many answers have been given to it: many fluids have been strongly recommended by different people. It must be well remembered that, as stated above, a sure and sovereign remedy has yet to be discovered, and failure may attend even the best suggested at present. Bearing this in mind, tree-growers will find in the following list the result of the experience of a number of observers, which may serve as a useful guide. It does not profess to be more than a summary, compiled from the researches of entomologists such as Mr. Comstock, Professor Riley, Mr. Hubbard; from suggestions by gardeners and others, embodied in various parliamentary and private documents; and from actual observation and experiment in this country: but it is believed that the information here given may be accepted and relied on.
Some of the substances here given are manifestly unsuitable for general use on account of their expense, at any rate in the open air. Yet it is well to include them, as they are all suggested in some work or other, or in the replies of gardeners and fruit-growers to parliamentary inquiries; and the objections to them ought also to be known:—
1. Alcohol. Will certainly kill any individual insect; but "sprayed over scale-insects produced no apparent effect" (Comstock).
2. Ammonia. Whether used pure (diluted) or in urine, damages the plants much more than it does the insects (Hubbard; Comstock).