Page:Growing Black Locust Trees.djvu/22

20 Natural or volunteer trees of various local species may be expected to come into black locust stands. Because of the open, light shade such stands act as a good "nurse" and favor trees that start from seeds blown in or dropped there by birds or animals.

Among the varieties of black locust the so-called shipmast locust is important because of the straightness of its trunk, its good rate of growth, and the good quality of wood (fig. 14). The main stem or trunk is excurrent, like that of pines and yellow poplar. It is found chiefly on Long Island, N. Y., where it is thought to have been introduced about 2 centuries ago from some unknown point in Virginia. Only rarely does it produce seed, and these are mostly infertile; thus shipmast locust is reproduced only vegetatively, by means of root cuttings (4 to 5 inches in length) and sprouts. (See Department of Agriculture Circ. No. 379, Shipmast Locust.)

The adult locust borer (Cyllene robiniae) is a handsome beetle, about one-half inch in length, black with yellow stripes, and with long horns or antennae. It is most frequently seen in late summer or early fall, feeding on the pollen of goldenrod. The borer is found in practically all parts of the United States where black locust is growing.

The injury is caused by the feeding of the larva or grub in the sapwood and heartwood of the trunk and of the larger branches. It makes large burrows which weaken the tree and sometimes result in its death by wind or heavy girdling. The eggs, which are laid in bark crevices, hatch into larvae or grubs that live over winter hidden in the inner bark. In the spring these larvae begin to burrow actively and feed vigorously on the wood of the tree until they pupate in July or August. The presence of the young borer is easily detected in the early spring. Pellets, damp or wet from the oozing sap, will be seen coming out of holes, mostly in the tree trunk where the bark is rough. Old attacks may be recognized by calloused swellings on the trunk or large branches.

Means of reducing borer attack on trees in forest plantations and method of control for use on individual dooryard trees are discussed on pages 22 to 25.

In its larval stages the locust twig borer (Ecdytolopha insiticiana), a moth insect, causes considerable damage by eating and boring in the young, tender growing twigs in the earlier part of the growing season. It is not known that it attacks any other part of the tree or at any other season. There are two generations a year, and the winter season is passed in the pupal stages in the ground. Adult moths of the first generation appear about May or June and those of the second generation in August or September.