Indian Meal Moth (Plodia interpunctella).—The larva of this moth feeds on the kernels of the harvested almonds when they are stored. Infestation usually takes place in storerooms or warehouses in which the nuts have been placed for a time. The warehouses become infested from old grain bags which have been kept there at one time or another. So far as known, infestation does not take place in the field. The larvae will continue to work in the stored almonds for a long time, doing a very great amount of damage ([fig. 25]). They may be controlled by thoroughly cleaning out the corners of the warehouse and thoroughly disinfecting. The nuts should be disinfected with carbon bisulphide (explosive when in the form of a gas mixed with air), or other means used to control insects in grain.[6] Prevention is far easier than the cure in this case.
Scale, aphis, diabrotica and other insects are sometimes found on the trees, but are generally not sufficiently troublesome to require special attention. Most of them are held in check by the control measures used for the more serious pests.
OTHER PESTS
Gophers.—These often do great damage to the trees by girdling them just below the surface of the ground, or if they do not actually girdle the trees, they cut them enough to devitalize them and, in addition, the wounds made by their gnawings frequently become infected with crown-gall organisms. The only safe means of control is the constant use of traps supplemented by poisoned bait.
Squirrels.—Squirrels are very troublesome, as they harvest a large amount of almonds before they are sufficiently ripe to be harvested by the grower. The use of poisoned grain or “gas,” if used over a large area of surrounding territory, will prevent serious depredations.
Birds.—Birds also carry off large amounts of almonds if the orchards are near open country or hills, especially if wooded. Crows, bluejays, blackbirds, yellow-hammers, robins and other similar birds are the worst offenders. Sometimes linnets eat off large numbers of fruit buds in the spring in a few of the newer sections where plantings are scattered. Sap-suckers have been known to girdle entire trees or large branches by cutting large numbers of holes in a series of lines close together around the trunk or limbs.
Morning-glory.—This is probably the worst of the weeds in almond orchards, and is the hardest to control. Sheep and chickens may be used with excellent results, provided care is taken to see that the sheep are not allowed to go hungry, for then they will bark the trunks of the trees very quickly. An excellent plan is to arrange gates so that the sheep must go through the orchard from pasture to get water. In passing back and forth they will forage over the entire orchard and dig up all the morning-glory in sight. Chickens are fond of the succulent new shoots, and will keep them below the ground until the underground stems and roots weaken and die. Cultivation throughout the growing season, often enough to prevent the morning-glory from developing any leaves for a whole year at least, and longer if necessary, will starve the plants to death.
VARIETIES
The problem of selecting varieties of almonds for planting in California is to choose the ones that are most marketable and at the same time to secure best results in cross-pollination. At the present time there are comparatively few varieties of almonds which have won and retained their popularity with the grower and the trade. There are a number of reasons for this condition. The cultural, climatic and soil conditions under which the almond thrives are much more limited than for most of the common deciduous fruits; the area of production in America is limited largely to California; the industry is comparatively new, and in general, there is not the great varietal variation in season, appearance, texture, flavor and behavior that is found in the apple, peach, pear and similar fruits. The comparatively rapid deterioration of fleshy fruits after ripening makes a succession of varieties desirable to extend the period of consumption. With almonds, the season of all varieties extends from one harvest to the next, if properly handled. Growers are, therefore, recommended to plant only standard, marketable varieties as far as possible.