Читать книгу The Pears of New York - U. P. Hedrick - Страница 34

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Several insect pests are very destructive to pear-trees, as many more are often troublesome, while perhaps in addition to the dozen that must always or occasionally be combatted some thirty or forty more have been listed as pear-pests. Young pear-trees are very susceptible to injuries of any kind and if beset by any of the common insect pests do not prosper. As the trees come to maturity, life and vigor of the tree may not be endangered by any but two or three of the worst pests, but the crop is always cut short by infestations of insects on any part of the plant which interferes with the normal life of the tree. The pests most destructive to the pear in New York, about in order of importance, are San Jose scale, psylla, codling-moth, pear-slug, and pear-leaf blister-mite.

San Jose scale (Aspidiotus perniciosus Comstock) is particularly harmful to tree and fruit of the pear. The pears, possibly, are malformed more and show the scales with their discoloration more plainly than the product of any other fruit-tree. A scale-infested pear-tree is easily recognized. Dead and dying twigs or branches and moribund trees are evidences of the dreaded pest. Examination shows the moribund parts to be covered with myriads of minute scales which give the infected bark a scurfy, ashy look. A reddish discoloration is discovered if the bark be cut or scraped. A foothold gained on trunk or branch, fruit and foliage are soon infected. Reproduction is continuous throughout the summer, and the scales increase by leaps and bounds. Smooth-barked young trees succumb within three or four years if the insects are unchecked; the rougher-barked old trees survive the pest indefinitely, although the vigor is lessened to the point of unproductiveness in many old orchards. Pear-growers find the lime-sulphur solution applied in the dormant season the most effective spray in combating San Jose scale. Several insect enemies of the scale help to keep the pest down. A quarter-century ago, it was feared that the pear industry of the State might be ruined by San Jose scale, but no energetic fruit-grower now fears the pest.

Next to San Jose scale, psylla is the most feared pest of the pear in New York. Indeed, this insect is much more difficult to combat successfully than scale, and were it as wide-spread, the pear industry in New York would be hard hit. The psylla is a minute, sucking insect, wingless in its immature stages, but winged and very active as an adult. They are nearly related to plant-lice, and like them suck the juices of the buds and new leaves. Like plant-lice also they reproduce very rapidly. The immature insects secrete a sticky honey-dew which becomes blackened with a fungus, and the presence of this blackish, sticky substance on foliage and branches is usually the first indication of the pest. The adult is about one-tenth inch long, with four membranous wings, the body dark in color and showing brownish-black markings. Seen through a hand lens, the mature insects look like tiny cicadas. The adults hibernate in crevices of the bark, and at the time buds are swelling in the spring come out to lay their eggs. The eggs hatch in two or three weeks, and there may be four or five broods in a season. The pest is best controlled by spraying with such contact insecticides as tobacco extract both to kill the hibernating insects and later the immature psylla. The winter strength of lime-sulphur solution will kill the eggs.

The apple-worm, the larva of the codling moth (Carpocapsa pomonella Linnaeus), destroys great quantities of pears year in and year out in New York, causing greater monetary loss to pear-growers than any other insect pest. The worm and its work scarcely need description—all know “wormy” apples and pears and the agent of the mischief. A pinkish-white, fleshy worm eats a cavity within the pear, usually through and around the core, and then eats its way out to the surface, after which it finds suitable shelter in a crevice of the bark and spins its cocoon. About the time apples blossom the larvae transform into small brown pupae, from which small moths emerge in two or three weeks. The moths are coppery-brown, small, with a wing expanse of about three-quarters inch, and very inconspicuous as they rest during the day on the bark of the pear-tree which they closely resemble; they fly only at dusk. The moth lays its eggs on leaves or the fruit itself and the young larvae immediately begin work on the nearest pear. Control consists in spraying with arsenate of lead. Two and sometimes three sprayings are necessary. The most important spraying is made just after the blossoms fall, while the calyx-cup is still open, so that the poison will lodge in the blossom-end of the upturned pear. Codling moth was once a most serious pest of the pear, but is now easily kept under control by seasonal applications of arsenate of lead.

The pear-slug (Caliroa cerasi Linnaeus), a generation ago, before spraying was common, did much damage to the pear in New York, but is now a negligible pest except in the orchards of the indifferent or slothful since it is easily controlled by spraying. The slugs are small, dark green shiny creatures which eat the surface of the leaves of pear, cherry, and plum. They devour the upper surface of the leaf leaving the veins and the tissues of the lower surface, which turn brown so that the infested tree has the aspect of having been scorched by fire. The slugs molt and finally lose their shiny coat and dirty green color, the full-grown larvae becoming clear yellow. The adult is one of the numerous saw-flys. Eggs are laid within the tissues of the leaves. There are two or three generations in a season. The slugs are most common in the hottest part of the summer or late in the summer. This pest is easily kept in check by applications of arsenate of lead.

The foliage of the pear, in common with that of the apple, is often seriously injured by a mite (Eriophyes pyri Pgst.) which burrows into the tissues of the leaves. The mites attack the young leaves causing reddish blisters which turn black. The blisters are thickened spots which are found to have a corky texture. The young fruits are sometimes attacked, in which case they are badly malformed. The mites are of microscopic size and can be seen only by the aid of a magnifying glass. They hibernate under the scales of the leaf-buds, and are thus ready to attack the young leaves as soon as they unfold, which they do by eating their way in from the under side and then by their work cause the characteristic swellings. As they mature, the mites come out and move to new places and start more colonies. In the autumn, they find their way to the maturing buds and go into winter quarters. An application of lime-sulphur solution at winter strength usually disposes of the mites; that put on for San Jose scale suffices for this pest also. Summer sprays do not reach the mites as they are then hidden within the leaves. The pest was once a serious menace to the pear, but with the advent of winter spraying has become of small importance.

Of the numerous other insects which occasionally become serious pests of the pear, at least twenty have been troublesome at one time or another in New York. Space does not permit a description of these minor pests—they are named as a matter of record. It is not necessary to give remedies for them, as all are controlled by the treatment of major pests which in most orchards need annual applications of one spray or another.

Several scale insects, other than San Jose scale, are more or less pestiferous in the pear-orchards of this State; commonest of these is the oyster-shell, which not infrequently does serious damage to young and unhealthy trees. The scurfy scale found chiefly on the apple sometimes becomes a pest on the pear. A hemispherical scale, about one-twelfth of an inch in length, known as the terrapin scale, now and then infests the pear, but is seldom if ever harmful. As a rule, the treatment for San Jose scale keeps all other scales in check, but all are more difficult to kill than the San Jose and in cases of troublesome infestations may require drastic treatment with a contact insecticide.

A great number of chewing insects, as distinguished from sucking insects, defoliate the pear when given an opportunity, but are kept in check by the treatment for codling moth. The much-dreaded browntail moth and gypsy moth now have a foothold in the State, but as yet can hardly be called pests although their advent threatens the pear industry as it does all other orchard industries. The bud-moth, seldom seen in well-cared-for orchards, is sometimes a vexatious visitor in pear-orchards. Three species of caterpillars, all most striking in appearance, the larval stages of tussock moths, infest pear-trees. These are the white-marked tussock moth, the rusty tussock moth, and the definite-marked tussock moth.

The pear-tree has its share of borers. A small, dark brown beetle, about one-third of an inch in length, the apple twig-borer, sometimes does considerable damage to young shoots of the pear. The flat-headed apple-tree borer works in the sap wood of the pear as in the apple. The shot-hole borer, a tiny insect, eats a small round hole in the trunk of the pear, as it does also in several fruits, but does little damage except in devitalized trees. The shot-borer, a tiny black beetle, one-tenth of an inch long, bores into twigs or small branches and sooner or later causes their death. None of these borers are very harmful on the pear in New York, but all must be reckoned with occasionally. All are difficult to control.

The pear thrips attack the newly opening flower- and leaf-buds and when the insect, a small winged creature with sucking mouth-parts, is abundant much damage is done. This pest in New York is chiefly confined to the Hudson River Valley. The European grain aphis, closely related to the destructive apple aphis, is sometimes a serious pest on pears. Both of these pests are comparatively easily controlled by timely applications of contact insecticides.

Lastly, there are several chewing insects which feed on the leaves of the pear, which, unless checked, sometimes become major pests for a season or two in an orchard here and there. All of them, fortunately, are controlled by the arsenical poisons which are necessary to keep the codling moth down. The pests are: Cigar case-bearer, green fruit worm, pistol case-bearer, and oblique-banded leaf-roller. With these, as with most of the other pests of the pear, cultivation to keep down all foreign vegetation, and orchard sanitation, consisting chiefly of the destruction of infested fruit, foliage, or wood, are essential preventives.