Growers' opinions differ as to the length of trunk an apple tree should have, and also as to whether there should be a main trunk above the principal lower limbs, but all agree that a few (some growers say five, four or even three) well-placed main limbs are better than a large number. These mains should start far enough from one another to avoid the danger of splitting when under load of fruit, and should be made to rebranch near the main trunk Some of these branches should be trained upward, the others more horizontally, so as to develop a well-rounded, symmetrical top. Four or five years' careful training should so fix the character of the tree as to obviate in great measure the necessity of subsequent prun ing. See PRUNING.
Insects.— Several hundred insects feed upon the apple, but the most of them are so well controlled by their enemies or by natural checks that their injuries are seldom noticed. There are, however, many that are frequently troublesome, among which the following are perhaps the most commonly destructive. In connection with the specific means of control here mentioned, the reader should refer to the general article FUNGICIDE. (1) Codlin moth (Carpocapsa pomonella) is perhaps the best known and most widely distributed apple pest. The eggs are laid upon the fruit, the larvae al most invariably entering the calyx, burrowing through the flesh and causing premature ripen ing. Since two or even three broods are pro duced in a season, the destruction of the first by spraying is of prime importance. This spraying must be done before the calyx closes, because the caterpillar's first meal must be pois oned, to accomplish which the sepals must not have closed. A second spraying is recommended a month later. The destruction of culls, cores and parings and the use of moth-traps in the windows of storage-rooms also assist in con trolling the pest. (2) Apple maggot (Rhag oletis pomonella), the footless grub (one-fifth inch long) of a two-winged fly, tunnels in the fruit and is especially troublesome in New York and New England, attacking thin-skinned summer and autumn varieties. Windfalls may be eaten by stock running in the orchard, and stored apples may be fumigated with carbon disulphide. (3) San Jose scale (Aspidio tits perniciosus), a minute scale insect of enormous prolificacy found upon many species of woody plants which in a few years die. When full grown it so closely resembles some of its relatives that a microscopic examination is necessary to determine its identity. When abundant, infested twigs have a somewhat scurvy appear ance resembling a coating of ashes. From be neath the female scale the young appear, crawl to new feeding ground, fix themselves and re produce with great rapidity. It has been esti mated from careful records of close observa tions that more than 3,000,000,000 scales may be produced in a single season from one female. Spraying with kerosene emulsion, lime, sulphur and salt solution, or fumigating with hydro cyanic acid gas, are the popular ways of com bating this pest. (4) Canker-worm, the larva of certain moths (species of Anisopteryx and Paleacrita), most common in the northeastern United States and adjoining Canada. They at tack the leaves of apple, pear and some other trees, entirely defoliating them when especially abundant. The wingless females crawl up the trunks and lay their eggs upon twigs or bark The larva, measuring-worms, appear shortly after the foliage from which, when disturbed, they drop at the ends of silk threads. If they reach the ground they climb the trunk to re sume feeding. Pupation occurs in the ground. This climbing habit of both females and larva, especially of the former, suggested impassable bands upon the trunk as a means of control. To be most effective these must be applied just before the female begins to climb, and since those of one species are active in the late fall and upon warm days during the winter, and those of the other in the spring, the bands must be kept in good condition during most of the year. (Consult New Hampshire Experiment
Station Bulletin, No. 85, 1901). (5) Tent cat erpillars, the larva of a moth (Clisiocampa americana), attack various trees in a large part of the United States and Canada. The eggs are deposited in gluey-looking masses upon the twigs in summer and hatch in very early spring. The larva are gregarious, and spin a protective web from which they emerge to feed. When numerous they frequently strip large limbs or even trees of foliage. Gathering the eggs dur ing the winter and cutting off the nests as soon as seen are the two most effective methods of control. Since several parasites attack the eggs of this moth, the egg masses should be kept out of doors in a place from which the parasites, but not the newly hatched worms, can escape. (6) Web worm (Hyphantria cunea) is a cater pillar similar in habits to the preceding, but en closing the foliage upon which it feeds inside a web until nearly full grown, when like the former species the larva disperse. The eggs are laid by a moth in late spring upon the undersides of leaves near the tips of branches of many trees, bushes and even clover. Cutting and burning is the most effective remedy. (7) The round-headed and the flat-headed borers are serious pests. They bore in the young wood, the latter mainly near the ground in the trunk, the former more frequently in the larger limbs. They are the larva of two beetles (re spectively, Saperda candida and Chrysobothris femorata). Their presence is indicated by the presence of chip-like castings at the mouths of their burrows. The only effective means of control are cutting out the larva or prodding them to death in their burrows with a flexible wire. The application of repellants to prevent the laying of eggs upon the trunks is sometimes recommended. (8) Woolly aphis (Schizoneura lanigera) often called American blight in Eng land and Australia, is a serious pest, especially upon young trees. Two forms of this insect appear; one above ground, the other upon the roots. The former, readily recognized by its woolly appearance, is easily controlled by kero sene emulsion; the latter is hard to fight with out injuring the trees. Tobacco dust worked into the ground seems to be the most effective and least harmful remedy. Nursery stock should always be carefully examined for this pest and treated, if necessary, before being planted. (9) Bud moth (Tmetocera ocellana), a tiny insect, the larvae of which appear in midsummer, pass the winter in the larval state and attack the opening buds and young leaves, over which they weave a little web in early spring, when they are most destructive. Paris green is effective. (10) Aphis fomi, the green apple leaf aphis, which injures the leaves of young trees and stunts the growth of the fruit. It can be controlled by spraying with lime sulphur solution in February or March, and by various insecticides, especially nicotine solu tions, later on. (11) Various caterpillars, es pecially the tent caterpillar, that of the gipsy moth and that of the brown-tail moth (qq.v.). The methods of controlling these insects are treated under their respective names. The cat erpillars of Tmetocera ocellana and Eccopsis ',talon° attack the flower-buds. (12) The pear thrips also attacks the blossoms. (13) The plum curculix Conotrachelus nenuphar, attacks the fruit, and is controllable by the same meth ods as the codlin moth. (14) The green-fruit worm, Xyliner, eats a cavity out of the side of the apple. See INsEcrici°E.