All of the trees in the hickory group are intolerant of shade and of competition with other trees. The more sunlight they can have the better. Most of us are familiar with the hickory tree standing alone in the cultivated field, which bears a heavy annual crop, when the neighbors at the edge of the forest bear sparingly. Hickories in forest growth put their energies into the formation of wood chiefly, and in the struggle for food and light devote very little energy to fruiting.
The best method for cultivation of hickories has been worked out only with the pecan up to the present time. With this species, it has been determined that clean cultivation with plenty of fertilization gives best results, as with apples. It is probable that Stringfellow's sod culture method will come next in order, and will perhaps be most generally used by nut orchardists, because it is less expensive and requires less labor. The sod culture method includes the idea of cutting all grass and weeds beneath the trees, in order to take away competition, allowing these vegetable substances to decompose beneath the trees and furnish food. There is no objection to adding artificial fertilizer, or a still greater amount of vegetable matter.
The enemies of the hickories are not many in the forest, where the balance of nature is maintained, but when man disturbs the balance of nature by planting hickories in large numbers in orchard form certain enemies increase, and must be met by our resources. Fungous and bacterial enemies are beginning to menace some varieties of the pecan in the South, and both in the North and in the South certain insect enemies are becoming important in relation to all valuable hickories.
The bark boring beetle (Scolytus) has been reported as destructive to hickories in some sections, the trees dying as a result of depredations of the larvae of this beetle.
I find a large borer at work on some of my hickories, but have not as yet determined its species. It may be the painted hickory borer (Cylene), or the locust borer. It makes a hole as large as a small lead pencil, directly into the trunk or limbs, and excavates long tunnels into the heart wood. The painted hickory borer is supposed to occur chiefly on dead and dying hickories, but the borer of which I speak is found in the vigorous young hickories in the vicinity of my locusts, which are riddled with locust borers.
In some localities involucre borers make tunnels between the nut and the involucre, interfering with the development of the kernel.
The hickory twig girdler (Oncideres) is abundant in some localities, but not as yet very destructive.
Hickory nut weevils destroy many nuts in some localities, and their colonies increase about individual trees markedly. In such cases, it is important to collect the entire crop each year from a given tree, taking pains to destroy all nuts which contain weevil larvae. These may be selected in a general way by dumping the freshly gathered nuts into a tub of water. Nuts containing weevil larvae will float for the most part, and in order to make sure of the destruction of larvae in the remaining nuts they may be placed in a closed receptacle, and carbon bisulphide poured over them.
One of the bud worms is sometimes very destructive to individual hickory trees which have developed colonies, the larvae destroying the axillary buds, and burrowing into the base of the petioles of leaves.
A new enemy which I found this year for the first time is the Conotrachelus juglandis. This beetle ordinarily lays its eggs in the involucre of the butternut. With the introduction of exotic walnuts, the beetle has changed its habits, and lays its eggs in the herbaceous shoots of walnuts and hickories. The larvae tunnel into the center of a shoot, and destroy it, or seriously interfere with its nutrition.