How to grow apple? Information about the cultivation, propagation, soils and fertilizers, harvesting and diseases of apple.
Propagation. New varieties of apples are propagated from seeds, but since seeds rarely improve upon the parent, seedlings are used chiefly to produce stocks for grafting or budding. Standard (that is, natural-sized) trees are so propagated. Dwarf trees result from grafting or budding the standard varieties upon the small-growing, almost bushlike varieties.
Much discussion has arisen concerning the relative advantages of grafting over budding, and also concerning methods of grafting. Opinions in the first case are very conflicting. In the latter they seem to favor the use of a small piece of apple root as stock (that is, the underground part of the graft) and a rather long scion (the shoot or twig that supplies the aerial parts of the graft), which should be set deeply in the soil of nursery or orchard. This procedure ensures the rooting of the scion and produces a tree that draws its nourishment from its own roots instead of from the nondescript roots of the seedling stock. In rigorous climates, hardy varieties are selected upon which to topwork less robust varieties and to increase their hardiness.
When the trees are set out, the tops must be cut back severely, to balance the root lost in transplanting from the nursery and to start the head at the proper height from the ground.
Growers’ opinions differ as to the length of trunk an apple tree should have, and also as to whether the main trunk should be allowed to extend above the principal lower limbs. Formerly six feet (1.8 meters) was the usual length of trunk desired, but half that length now is preferred, and in the West Central states even less than that. Most growers agree that a few well-placed main limbs are better than a large number. These should start far enough from one another to avoid the danger of splitting under the load of fruit.
Principal limbs should be made to rebranch near the main trunk. Some of these branches should be trained upward and the others more horizontally, in order to develop a well-rounded, symmetrical top. Also trees with short bodies and low heads are less likely to be injured by wind and sunscald than those with high heads and long bodies. Four or five years are needed to establish the desired characteristics.
Soils and Fertilizers. Apples thrive in nearly all kinds of soils, certain varieties being better adapted to light soils and others to heavy. The great majority of varieties succeed best in medium to clayey loams, especially if the terrain is somewhat elevated, inclined or rolling, and the climate is clear and dry. Since air and water drainage are usually good in such places, the fruit produced is generally of fine color, flavor, and size. In lowlands and in damp climates the fruit is usually of inferior quality and the trees more susceptible to fungous attacks.
The preparation of the land does not differ materially from that for other crops such as corn or potatoes, either of which is often grown the previous season in order to fit the land for planting the orchard. The trees may be set out in spring or autumn, and the cost of cultivation may be met by cropping the land for the first few years with potatoes, melons, or some other low-growing, intertilled crop.
Nitrogen occupies a more important place in orchard fertilizers than any of the other nutrient elements. Many apple orchards have grown to maturity and produced heavy crops when nitrogen was the only fertilizer applied. However, the value of potash, phosphate, magnesium, and other essential elements has more recently been shown in certain restricted areas.
Orchards in permanent sod or nonlegume cover crops require heavier fertilization than those in cultivation or in legume cover crops. If cover crops such as clover, vetches, or cowpeas are grown, they will supply all the nitrogen needed. Indeed, if such crops are long continued or if several very heavy crops are turned under, too much nitrogen may accumulate and recourse to a cereal crop may be necessary to remove the excess. Lack of nitrogen is indicated by pale green or yellowish foliage.
Harvesting. As the fruit ripens, the starch it contains becomes changed into sugar, the leaf green is replaced by tints characteristic of the variety, and the flow of sap into the fruit diminishes until the apple has attained full size and weight. Since the changes that subsequently take place are mainly chemical and continue independently of the tree, the fruit may be picked. Fruitgrowers agree upon this time, which they determine for each variety from experience. The fruits are still hard but have brown seeds, and having reached the proper development, may be picked by slightly twisting the stem without danger of breaking the twig upon which it is borne, thus preventing a loss of fruit-bearing wood. Fruits gathered at this time and ripened properly are superior to those allowed to hang longer upon the tree.
Apples should be stored as soon as possible after picking. The temperature should be kept uniform, just above 32° F (0° C), so as to check the ripening process. Drafts should be avoided,t since they hasten decay and increase shriveling; hence closed packages are better than shelves. Odors should be excluded.
Apple Pests. Several hundred insects feed upon the apple, but most of them are so well controlled by their enemies or by natural checks that their injuries seldom are noticed. There are however, many insects that can be destructive. The following are the most common.
( 1 ) Codlin moth ( Carpocapsa pomonella ) is perhaps the best known and most widely distributed apple pest. Its eggs are laid upon the fruit, and the larvae almost invariably enter the calyx, burrow through the flesh, and cause premature ripening. Since two or even three broods are produced 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 poisoned.
( 2 ) Apple maggot ( Rhagoletis pomonella ), the footless grub (% inch [1.3 mm] long) of a two-winged fly, tunnels in the fruit and is especially troublesome in New York and New England. It attacks thin-skinned summer and autumn varieties.
(3) San José scale (Aspidiotus perniciosus) is a minute scale insect of enormous prolificacy which is found upon many species of woody plants. When full-grown it so closely resembles some of its relatives that a microscopic examination is necessary to determine its identity. When abundantly infested, the twigs have a somewhat scurvy appearance resembling a coating of ashes. The young appear from beneath the female scale,
crawl to a new feeding ground, fix themselves, and reproduce with great rapidity. It has been estimated from careful records of close observations that more than 3,000,000,000 scales may be produced in a single season from one female.
(4) Cankerworm is the larva of any one of certain moth species (Anisopteryx and Paleacrita), most common in the northeastern United States and adjoining Canada. The caterpillars attack the leaves of apple, pear, and some other trees, causing complete defoliation when infestation is especially abundant. The wingless females crawl up the trunks and lay their eggs upon twigs or bark. The larvae (measuring-worms) appear shortly after the foliage appears. When disturbed, they drop at the ends of silk threads; if they reach the ground they climb the trunk to resume feeding. Pupation occurs in the ground.
(5) Tent caterpillars, the larvae 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 early spring. The larvae are gregarious, and spin a protective web from which they emerge to feed. When numerous they can strip the tree of foliage.
(6) Webworm (Hyphantria cunea) is a caterpillar similar in habits to the preceding, except that it encloses the foliage upon which it feeds inside a web. When nearly full-grown, the larvae disperse. The eggs are laid by the moth in late spring upon the undersides of leaves near the tips of branches of many trees. Bushes and even clover are also hosts.
(7) The round-headed and the flat-headed borers are serious pests. They bore into the young wood, the latter mainly near the ground in the trunk, the former more frequently in the larger limbs. They are the larvae of two beetles (respectively, Saperda Candida and Chrysobothris femorata). Their presence is indicated by the presence of chiplike castings at the mouth of their burrows.
(8) Woolly aphis (Schizoneura lanigera), in England and Australia often called American blight, is a serious pest, especially upon young trees. Two forms of this insect appear: one above ground and the other upon the roots. The former, readily recognized by its woolly appearance, is controlled easily; the latter is hard to fight without 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) is another apple pest. The larvae of this tiny insect appear in midsummer, pass the winter in the larval state, and in early spring, attack the opening buds and young leaves, over which they weave a little web.
(10) Aphis fomi, the green-apple leaf aphis, injures the leaves of young trees and stunts the growth of the fruit. It can be controlled by spraying with lime-sulfur solution in February or March, and by various insecticides, especially nicotine solutions, later on.
(11) Various caterpillars, especially the tent caterpillar, that of the gypsy moth (q.v.), and that of the brown-tail moth also are serious apple pests. The caterpillars of Tmetocera ocelana and Eccopsis malana attack the flower buds.
( 12) The pear thrips also attack the blossoms.
(13) The plum curculio, Conotrachelus menuphar, attacks the fruit, and is controllable by the same methods as the codlin moth.
(14) The green-fruit worm (Xyliner) eats a cavity out of the side of the apple.
( 15 ) Spider mites of the general family Tetranychidae recently have become extremely destructive orchard pests, and their control demands careful timing of miticide applications.
(16) The red-banded leaf roller, Argyrotaenia velutinana, has become important since the advent of certain organic insecticides that have reduced the number of natural parasites of this insect.
Mice and rabbits are likely to damage young trees during the winter months, especially when the ground is covered with snow and food is difficult to find.
Apple Diseases. Apple scab ( Fusicladium dendriticum ) is probably the most serious apple disease, since it causes the loss of much fruit and injures the appearance of much more. It appears as black spots with grayish border on apples and pears that have not been sprayed. Often the abundance of the confluent spots prevents the normal development of the fruit, which becomes lopsided. The leaves are also attacked, but the markings are not so pronounced.
Rust ( Roestelia pirata ) appears upon the foliage in early summer as more or less confluent orange spots. The fruit is also destroyed. The spores of this fungus will not germinate upon the apple but find a congenial host in the juniper or cedar. These, when matured in the following spring, look something like orange-yellow sponge. The spores will not germinate upon the cedar, but will upon the apple. Sometimes the fungus perpetuates itself by its mycelium (branching filaments), which may live from year to year upon the young twigs and buds of the apple. Destruction of the cedars and spraying are effective.
Apple canker ( Nectria ditissima ) destroys the bark and younger wood, and eventually the tree, but small areas may be cut out and the wounds painted with Bordeaux mixture. In fact, since this disease gains entrance through wounds, these should all be similarly treated. Burning badly infested trees is the only means of checking the spread of this disease.
Powdery mildew (podosphaera oxycanthae), a grayish growth upon the foliage, is often troublesome in the South upon young trees and seedlings in the nursery. It may readily be controlled by a standard fungicide. Bitter rot (Glomorella rufomasulans) appears upon the fruit as brown spots extending until they often involve the whole apple. It may attack at any time and is especially destructive to the early varieties, more in the South than in the North.
Black rot (Sphaeropsis malorum) resembles bitter rot and is similarly controlled.
Two important bacterial pests are pear blight (Bacillus amylavorus), which causes cankers on the limbs and trunks, and crown gall (Bacterium tumifaciens), causing swellings on the trunk and roots just below the surface of the ground. Oregon canker is Neofabraen malicorticis.