In the line of preventives and remedies there is nothing better than clean cultivation about the trees, and annual examination of each tree early in summer and the crushing of every borer found. The next best thing, in the way of a preventive, is to wrap the stems from a little below the surface of the ground to a foot or more above it with heavy paper, cloth, or bark of some kind, to keep the moth from laying her eggs on the bark of the tree. I have used common tar paper for this purpose, not only because it is very cheap and does not decay when exposed to the weather, but the exhalation or odor of tar seems to be offensive to the moths. In the use of this material I have never found that it was in the least injurious to the bark underneath. Painting the stems with soap, cement, clay, or even common mineral paints, will answer very well if a little care is given to keeping down the number of insects by removing the larger part of the borers with knife or gouge.
In recent years a pest known as the "shot-hole borer" (Scolytus rugulosus) has appeared in many and widely separated localities, in both the Eastern and Western States, attacking the almond, peach and plum tree. It is supposed to have been introduced from Europe with imported nursery stock, and thence rapidly distributed, by similar means, through the country. In its perfect stages it is a minute brown beetle, about one-twelfth of an inch long and one-thirtieth of an inch in diameter. This pest appears about midsummer, boring numerous minute holes through the bark and into the sapwood underneath, and in this the female deposits her eggs, and from these are hatched the little grubs found later feeding on the soft inner bark and alburnous matter beneath it. From every hole made in the bark a small globule of gum will soon appear, drying upon the surface—thence onward until autumn—and glistening in the sun, an immutable sign of the presence of a minute but destructive enemy.
When the beetles and their eggs are once in possession there is no practical way known of removing them, and the best thing to be done is to cut down and burn every infested tree, and just as soon as it is known to be in this condition. There are also several indigenous species of bark beetles, which will very likely attack almond trees as soon as they are as abundant as peach trees, but all may be destroyed with the same, or very similar weapons and materials.
What are called preventives consist mainly of substances to be applied to the stems in a semi-liquid form, and of such a nature as to be offensive to the beetles because of their odor, taste, or because so hard that the insects cannot cut through them with their mandibles. Common lime whitewash, soft soap, whale-oil soap, or a thin mineral paint made of pure linseed oil, will answer very well for this purpose if applied often enough to keep the bark constantly coated.
Of the fungous diseases affecting the almond in this country, very little is as yet known, although we may safely include under this head all those that have been inimical to the peach, for the transition from this tree to the almond would only be a natural sequence. The peach-leaf curl (Taphrina deformans) would not be far from home on the almond leaf, neither could we expect that almond orchards would be wholly exempt from that mysteriously distributed and uncontrollable disease known as "peach yellows."
In California an almond-leaf blight has already appeared and seriously affected the trees in some of the orchards. It is caused by a fungus known as Cercospora circumscissa Sacc. This fungus attacks the leaves and young twigs, causing the former to fall off early in the season, thereby checking the growth of the tree and preventing the maturing of the fruit. It is thought that remedies may be applied to check this disease, and there will probably be some form of copper solution employed for destroying it, as with various species of fungi on other kinds of fruit trees.