Kitabı oku: «American Pomology. Apples», sayfa 9

DWARFING THE APPLE

Apples are generally dwarfed by working them upon the French Paradise stock, which is a very diminutive tree or bush, seldom rising more than a few feet high. This is the true stock for those who wish to indulge in the luxury of dwarf apple trees. Such are very appropriate for the small garden, or for the specimen grounds of a nursery establishment, and they sometimes make beautiful objects in the lawn or among the shrubbery, but they are wholly unsuited for orchard planting, as many a poor deluded purchaser has found out to his sorrow, a few years after having been beguiled by the smooth-spoken tree peddlers, who have sold many thousands through the country to farmers to plant as orchard trees.

There is a more vigorous stock which has been used for the same purpose, but it possesses much less dwarfing power. It is called the Doucin, or English dwarfing stock. This, however, exerts so little of the dwarfing influence, that at the end of eight or ten years the trees are generally about as large as those worked upon free stocks; but it happens unfortunately that early fruitage, the great object of dwarfing, is not attained by their use, for they will not have produced any more fruit than the common trees similarly treated.

By Root Pruning.—Among the many valuable hints which horticulturists have received, with the beautiful flowering and other plants, from our antipodes in the "Flowery Land," none has been of greater value than the practice of root-pruning. In this art of dwarfing even the large forest trees by mutilations of the roots and by other means, this curious people excel all others, as has frequently been stated. In Europe, and in this country also, root-pruning has been extensively practiced with the effect of partially dwarfing the trees, but more especially with the object of inducing prematurely the fruitfulness we so much desire, and which is a natural result of the diminished supplies of crude sap furnished by the contracted roots of a tree that has been treated in this manner. The balance between the wood-growth by extension, and that which results in fruitful spurs is sooner established, and the sap is directed to the formation and support of the fruit.

We should not commence the application of this severe treatment until our trees have been allowed to establish themselves firmly in their stations, unless we desire at the same time to produce decided dwarfs by means of root-pruning. In this case the treatment may be commenced in the nursery itself; the stocks should be transplanted once or oftener before being worked, and the young trees should be moved annually, which will so shorten the roots as to make them a mass of fibres, occupying the whole soil close about their main divisions, and the subsequent removals can then be easily effected, with but a slight check to the tree, which becomes furnished with fruit spurs at a very early period of its existence, instead of its requiring years to reach its natural period of fruitfulness, as is the case with some varieties, particularly of the pear.

As generally practiced, however, root-pruning is postponed until the trees have made a free and vigorous growth, and have become well established in their stations. Then if the growth be too vigorous, and there do not appear any indications of the formation of fruit spurs, as is often the case in the fertile soils of the West, our impatient orchardists complain of the barrenness of their trees, and seek a remedy in root-pruning. This is generally performed with a sharp spade, with which a trench is dug in a circle around the tree. The excavation should be deep enough to reach all of the lateral roots; these are generally within a foot of the surface. The ditch need not be much wider than the spade, and the soil can be thrown back at once, but all the roots should be severed, if we desire to produce the effect of checking the wood-growth. The diameter of this circle will depend upon the size and vigor of the tree to be operated upon. As a general rule, it may be made in the proportion of one foot to each inch of the tree's diameter. The work may be done at any time after the spring growth has begun to harden, or during the autumn and winter, and until the buds are about to break in the spring. The operation is wonderfully conducive to the end we have in view, and we often see a vigorously growing but barren subject, transformed in a single season into a fruitful tree, covered with blossom-bearing spurs that are full of promise of delicious fruits. In some varieties, however, these fruit spurs require more than a single season for their perfection.

Now it may be objected that this labor will be expensive, and so it is, as all hard work with the spade must be; but what of that, when we consider the happy results that ensue in golden harvests. But it has been suggested that this labor may be performed by farm machinery, using a strong plow, or rather a sharp cutter attached to a plow beam, and drawn by a powerful team at the requisite distance on either side of the rows of trees, and in directions crossing each other at right angles. This, of course, like all mere mechanical applications, must be uniform, whether the necessities of the trees be equal or not; whereas, by hand-labor, we may vary the distance at which the roots are to be cut, according to the vigor and size of the trees demanding the treatment.

This topic will be again referred to in the chapter on Pruning, where also it will be necessary to recur to the subject of Training, which was incidentally alluded to in connection with Dwarfing.

CHAPTER V

DISEASES

DIFFICULTIES IN THE OUTSET—WHAT CONSTITUTES DISEASED ACTION—NO ANALOGY TO ANIMAL SICKNESSES—CONGENITAL DEFECTS—DEBILITY. DEFICIENT STRENGTH OF FIBRES—DEFECTIVE FOLIAGE—IMPERFECT AND REDUNDANT BLOSSOMS—THE CIVILIZED AND CULTIVATED PLANT MAY BE ABNORMAL ALTOGETHER—UNSATISFACTORY ACCOUNTS OF DISEASES IN PLANTS—LANKESTER'S CLASSIFICATION CONSIDERED—EFFECTS OF THE EXCESS OR PAUCITY OF MOISTURE, HEAT, AND LIGHT—MODE OF ACTION OF FROST—INJURY RATHER REFERRIBLE TO THE CONDITION OF THE CIRCULATION THAN TO THE DEGREE OF COLD IN MANY HARDY PLANTS—INFLUENCE OF THE SOIL—LIGHT THE GREAT STIMULUS, ITS WITHDRAWAL SUSPENDS HEALTHY ACTION—ITS SUDDEN RESTORATION CAUSES DEATH BY SUN SCALD—INJURY BY SUNSHINE IN WINTER—POISONOUS GASES—MIASMATA—POISONS IN THE SOIL—PARASITIC PLANTS, EPIPHITES, FUNGI, PEAR BLIGHT—VARIOUS THEORIES—WHAT WE KNOW, AND WHAT WE DON'T KNOW—TREATMENT—ROOT PRUNING SUGGESTED—SATISFACTORY RESULTS—MILDEW BLIGHT IN PEACH AND APPLE—TWIG BLIGHT IN APPLE AND QUINCE—THE APPLE BLIGHT—BITTER ROT—CRACKED FRUIT—SCAB—MILDEWS—KIRTLAND'S VIEWS AND SUGGESTED REMEDY—WOUNDS AND INSECTS—NEEDING THE AID OF SURGERY RATHER THAN MEDICINE—DESTRUCTION OF FOLIAGE BY INSECTS IMPAIRS THE HEALTHY CONDITION OF THE PLANT—RESUME—SELECT HEALTHY TREES OF HEALTHY VARIETIES—EMPIRICAL CHARACTER OF TREATMENT USUALLY RECOMMENDED FOR DISEASED TREES—THE BLACK KNOT—THE ROT AND MILDEW OF THE GRAPE.

In opening a discussion upon the nosology of vegetation, it may be expected that one who had spent many years of his life in the investigation of the diseases of the human family, and at the same time was something of a student of comparative anatomy and physiology, tracing analogies between the animal and vegetable kingdoms, should be familiar also with the diseases of plants. Such an anticipation, it is feared, will not, in the present instance, be realized. Indeed, the writer feels very much at a loss how to proceed in discussing this branch of the subject, and hardly knows what departures from undoubted health and vigor should be considered worthy of the title of disease. Nor is it easy to trace the causes of the conditions that are generally viewed in the light of maladies. We find the manifestations both in the tree or plant, and in its several parts, and also in the products which chiefly interest us; the fruits themselves, are often deteriorated by what is called diseased action of different kinds. The analogy to diseases of animals is certainly not very distinct. We do not find anything like fevers, or gout, or rheumatism, in plants, but we may consider some of their conditions somewhat in the light of dropsies, and plethora or hypertrophy on the one hand, and of anæmia or atrophy upon the other; we may consider canker and the death of some parts of a plant analogous to gangrene, and mortification in the animal subject. Then again we find congenital defects in individuals among plants, just as we do among animals. Some are always less vigorous than others, and thus certain varieties seem possessed of a degree of inherent disease that perpetually prevents them from displaying the requisite strength and vigor which we so much desire in our plantations. Certain varieties that, from the size and excellence of their fruits, have attracted the attention of pomologists, are so deficient in health and vigor as to be considered diseased, and are therefore very properly condemned as unworthy a place in our orchards and gardens; others appear simply deficient in the production of some one part, as is illustrated by the inferior strength of the woody fibres of some trees, which break easily under the weight of their own fruit, and thus destroy the symmetry of the tree and diminish its productiveness. Others have defective foliage, which is attended by the imperfect performance of the functions of growth, both in the fruit and in the sustaining woody fibres; others again produce defective blossoms with either a redundancy or deficiency of the parts that are necessary for the production of the seeds needed for the perpetuation of the species. When the parts are deficient, the flowers are called barren or infertile. A redundancy or multiplication of parts is seen in double flowers of our gardens, where they are much prized for their beauty, though considered monstrosities by the botanist, and perhaps properly referred to diseased action by the nosologist.

It is evident, that very often the conditions of a plant and its products, which we most highly prize, and towards which all our efforts in its culture are directed, are really departures from the natural and healthful status; in other words, what we covet, is really a state of diseased and abnormal action. With the other secondary objects of occupying and ornamenting the barren wastes of the earth with plants, and thus supplying food to hosts of insects, and to the higher animals, nature also has primarily in view, the production of perfect seeds for the perpetuation of their species, by the plants that are profusely scattered over the globe. Man, on the contrary, often rejects the true seeds as worthless when compared to their juicy fleshy envelopes that constitute his favorite fruits, or the enlarged and succulent roots, tubers, stalks, and leaves, that characterize his garden vegetables and field crops; while in the grains proper he seeks sustenance in the true seeds, which become the object of his greatest care and ingenuity to enlarge, to increase, and to develop, particularly in regard to their nutritive qualities.

Most writers upon the diseases of plants have given us very indistinct notions upon the subject, and have done very little to enlighten their readers; while they have written voluminously upon the unhealthy and unsatisfactory condition of certain vegetables, and have given us most extensive accounts of the treatment by which they propose to remedy the evils complained of, we gather little of the information needed to enable us to understand the true state of the case, or of the causes of the disease, if it is to be considered such. The reader need not expect that he will be more enlightened by this chapter than he has been by the essays to which reference is here made, but he will be led to a consideration of some of the causes of those departures from health and vigor which are considered diseased action, and in this way he may possibly be put upon the track which will lead him to the avoidance of disastrous results. More than this will not be attempted.

Perhaps the most satisfactory account of diseases of plants is that given by Lankester, in which he divides them according to their causes, as follows:

1st—Those produced by changes in the external conditions of life, such as redundancy or deficiency of the ingredients of soil, of light, of heat, air, and moisture.

2d—Those produced by poisonous agencies, as by injurious gases, miasmata in the air, or by poisons in the soil.

3d—Those arising from the growth of parasitic plants, such as the various Fungi, Dodder, Mistletoe, etc.

4th—Such as are caused by mechanical injuries or wounds, and by the attacks of insects.

These may be considered separately: 1st—It may be assumed, and has been already well established by botanists, that every plant has its own peculiar constitution, adapting it to certain atmospheric conditions, and that for its healthful and successful culture, these must be understood and adhered to, within comparatively narrow limits. Tropical plants, as is well known, cannot be cultivated beyond their natural limits, except under circumstances where their natural conditions are nearly imitated by the gardener; and even in our stoves and hot-houses, these plants do not compare in vigor with their fellows that luxuriate in the hot and steaming atmosphere of the tropics, under the stronger light of such a clime as is natural to them. On the contrary, the plants of northern latitudes will not grow and produce seeds where temperature is too elevated. Those from a humid atmosphere suffer in an arid clime, and those which thrive in dry sandy regions suffer equally when introduced into a humid atmosphere.

Thus we find, that where there is too much moisture for some of our cultivated plants, they are inclined to be too succulent, and this very excess may produce a dropsical condition that is really a state of disease. Thus we suffer in a loss of fruit, which will fall badly before its period of maturity, and that which remains its full time is found to be thin and watery, deficient in the high spicy aromatic flavor which is so highly appreciated by the connoisseur of these choice products. When, on the other hand, the arid character of the soil and climate prevail to an extent that is uncongenial to any particular fruit, we shall find that its growth is arrested, and that its highest qualities are not adequately developed: this is frequently observed in an unusually dry season—and in California, where irrigation is required to enable the orchardist to produce some of the succulent fruits, the most remarkable size and beauty have been attained, but we are told that it was often at the expense of the desired flavor that the same varieties acquire, under circumstances more advantageous to the development of their superior qualities.

So in many of our fruits, the successful results depend upon the hygrometric condition of the atmosphere, and Liebig suggests that a very prolific source of diseased action in plants, arises from the suppressed evaporation and transpiration consequent upon such atmospheric conditions.

Too much moisture prevailing at the time of the blossoming of our fruits, especially moisture precipitated in the form of rain during this period, is sometimes disastrous to our crops, both of cereals and of orchard fruits. Continuous showers prevent the development of the pollen-grains, and their transfer to the stigmas of the blossoms, so that the fruit does not set well. Fortunately this does not often occur in our glorious climate, which is so highly favored by an abundance of light and sunshine, which are the great and essential stimuli of the higher orders of plants. The loss of our fruit crops in some parts of the Ohio Valley in the years 1862, 1865, and 1866, was fairly attributed to this cause.

We must not overlook the unhealthy influences produced by an excess of moisture in the earth. Many plants that naturally delight in a dry porous soil, become weak, unfruitful, or even seriously diseased when they are planted in low wet grounds, or upon such as are underlaid by a very tenacious sub-soil, while an opposite condition is equally unfavorably to those that are naturally more aquatic in their tastes and habits. In the former case we learn to avoid such soils and situations, unless we are able to change their character in this respect by thorough under-draining, which will completely remove the evil, and the remedy becomes merely a question of expense.

A certain amount of temperature may be assumed as requisite to every plant, or rather it may be affirmed that some plants cannot exist and thrive except within a certain range, and it has been asserted that each class of plants requires a mean temperature for the year that shall not vary many degrees: the range of this variation has perhaps never been satisfactorily ascertained. But it is well known, that both heat and frost act injuriously upon vegetation. Mr. Lindley tells us that "the extreme limits of temperature which vegetables are capable of bearing, without destruction of their vitality, have not been determined with precision." When the temperature is maintained at a higher point than is natural, the plant is excited to undue activity of growth; but this is attended with an enfeebled condition, often seen in badly managed green-houses. Mr. Knight found that certain plants were rendered abortive by the production of male flowers only, when exposed to too great heat, and by an opposite treatment, when subjected to a low temperature for a long time, others produced only female flowers. In some plants a high degree of heat, with moisture, results in the production of leaves only, and Humboldt found that wheat was grown about Xalapa, Mexico, as a fodder plant, because it produced an abundance of grass, but did not form ears nor grain.

A diminished temperature, on the contrary, removes the stimulus of growth, and leads to the suspension of all vital action in proportion to its reduction. At the freezing point it is probable that all such action ceases, though in this regard there is great difference among plants; the mosses and lichens will flourish, and the Chickweed will vegetate and blossom at a temperature very little above freezing. The access of frost, after vegetation has somewhat advanced, often proves very disastrous, and we not unfrequently lose our crops of fruit by such an occurrence during the period of blossoming, or even afterward.

Some plants in a dormant condition, will endure uninjured a great depression of temperature, while others will be destroyed by the slightest approach of frost. According to De Candolle, this may depend upon the greater or less amount of water they contain, upon the greater or less viscidity of their fluids, or the rapidity with which these fluids circulate. Those with larger cells he thinks most easily injured by frost, and those which contain a great deal of air are able to resist it best. The freezing point will vary according to the quality of the sap, for we know that different vegetable juices congeal at different temperatures. The manner in which cold acts upon plants depends upon their physical structure. Lindley says, freezing is attended with the following effects:—The fluids contained within the cells of tissue are congealed and expanded—this produces a laceration of the cell-walls, and impairs excitability by the unnatural extension to which the cells are subjected; the air is expelled from the air-vessels and introduced into parts naturally intended to contain only fluid; the green coloring matter and other secretions are decomposed, and the vital fluid or latex is destroyed, and the action of its vessels is paralyzed. The interior of the tubes, in which fluid is conveyed, is obstructed by a thickening of their sides. So we have as a result, both mechanical, chemical, and vital changes.¹⁵

Our hardy fruit trees are woody perennials that hybernate during the winter. Yet we find that even these suffer upon some occasions from a great depression of temperature; it has been asserted that a certain degree of cold would inevitably destroy the blossom buds at least, and we often find that the bark is burst off from the wood, and in some instances the wood itself is so injured as to suffer from a kind of decomposition, and to become affected with a change generally known as the dry rot, losing its elasticity and hardness, and acquiring a whitish color, which is supposed may arise from the introduction of the mycelia of fungous growths. Now it is believed that these injuries do not arise so directly from the degree of cold to which the tree has been exposed, as to the condition of its circulation at the time of the exposure. If the sap have been excited by mild or warm weather, as is so apt to be the case in our changeable climate, the sudden depression of temperature will produce disastrous effects, even when the cold has not been very severe. This is manifested by the bursting of the bark in young trees in the early part of winter, while they are yet holding their leaves, and of course having a circulation somewhat active. Hence the importance, now very well understood by our nurserymen, of checking the growth of young trees in time to have their terminal buds thoroughly ripened before the approach of frost. This, to a certain extent, is subject to our control; but we cannot foresee the character of the seasons upon which the safety of our orchard trees will, in a great measure, depend, and they are less easily managed. When the autumn is dry, and continued late into winter, as sometimes happens, we see a perfect ripening of the wood, with a great development of blossom buds, and then we may confidently calculate upon the safety of our fruits, provided they be not exposed to a warm period at mid-winter, that shall excite some activity in their circulation, which would suffer terribly from any sudden and great depression of temperature such as frequently occurs, carrying the mercury from summer heat to a point below zero, in a few hours. Such a change has amounted to 68 degrees in nine hours.¹⁶

The influence exerted by the soil upon the healthiness or unhealthiness of our trees has already been alluded to incidentally, but it is an important subject of inquiry whether this may arise from a redundancy or a paucity of some particular ingredients necessary to sustain the plants we desire to cultivate. Liebig has pointed out how chemistry may be brought to our assistance in solving such a question. As all the inorganic elements found in a tree and its fruits, must have been derived from the soil in which it grew, he suggested that the ashes of the plant would show us exactly what it needed, and then an examination of the soils would inform us whether they contained all the necessary elements, and in the right proportion. Hence arose the doctrine and the practice of applying special manures, which has been so fashionable in our day. Though there be many doubters as to the efficacy of such investigations and practices, most sensible and enlightened agriculturists admit the truths which Liebig has propounded.

Light is the great stimulus of vegetation, an essential element to its existence: its withdrawal is followed by an arrest of some of the most important functions of vitality, and yet we find that there is a great difference among different species, as to their requirements of this element, and also that various parts and several products of vegetation require very different degrees of light for their perfection. It is also found that a sudden exposure of parts from which it had been withheld, is often attended with disastrous consequences. Its withdrawal does not so immediately destroy the plant, being attended with the etiolation of the parts that are usually colored, but a sudden re-exposure to the sun's rays will now destroy the plant. So the removal of a portion of the foliage from a tree, or the exposure of the bare stem of one that had been previously sheltered, is often attended with severe effects, known as sun-scald—for which there is no remedy, but very easy modes of prevention. The best of these is to provide against the evil by reserving the lower branches to shade the stem. There are other excellent reasons for this practice, which will be brought forward in the chapter on Pruning.

Frequently, however, the nurseryman, or perhaps the injudicious efforts of the planter himself, may have removed all the side branches of the young tree, and as these cannot be replaced, we may substitute for them a shelter from the scorching sun to which the newly planted tree is exposed. This may be done by tacking two narrow boards together at their edges, like a gutter spout, and setting them upright on the south side of the tree to shade it. A wisp of straw, tied loosely to the stem, will answer a very good purpose; but both of these appliances are objectionable, because they furnish a shelter for insects, and thus they fall short of the natural shading of the stem by the foliage of its own branches.

It is not only the scorching suns of summer that damage our young trees that are thus exposed by injudicious trimming. Even the bright rays of a mid-winter sun, falling upon the frozen stem, will often effect the most serious damage, and should be guarded against with equal care; but here the natural protection will answer, for the shade of the naked spray of the laterals is found all-sufficient in the well-trained tree.

2d—To resume the consideration of Lankester's causes of disease, it must be admitted that some diseased conditions may be produced by poisonous gases, but the usual result will be the death of plants confined in such an atmosphere. The natural power of diffusion of all gases among one another in the open air, prevents the danger that would ensue in a confined situation. The accidental production of sulphurous and other poisonous gas, or the escape of smoke from the flues or from the tobacco-pan in the green-house, sometimes produces the most disastrous effects upon the plants subjected to their action. So, in crowded cities, it often happens that the effects of coal smoke and other gases, generated in the furnaces and manufactories, are very injurious to vegetation. The coal soot falls in flakes like lamp-black, which covers the surface and obstructs the transpiration of the stomata, and thus seriously affects the health of plants in such situations.

The action of miasmata, suggested by Lankester, is as obscure in the effects produced upon plants as in those upon animals. The presence of these atmospheric conditions cannot be detected by any of our tests, nor can their effects be prevented by any means in our power; we know little or nothing about their characters, yet we cannot deny their existence: finally, they serve as a very convenient explanation, though a very unsatisfactory one, for the incursions of maladies that are of an obscure or unknown character. Whether of a miasmatic nature or not, no one can deny the existence of certain atmospheric conditions, which appear to produce disastrous effects upon some of our vegetable productions whether these be inherent to the air itself, or are only conveyed by it from one place to another. The inexplicable potato disease may owe its origin and diffusion to such a cause, and the grape malady, which appears to be dependent upon atmospheric causes, may at least be carried from one vine to another upon this medium, in the form of the minute spores or seeds of the fungi that are believed to be the cause of the trouble.¹⁷

Poisons in the soil are frequently very deleterious to vegetation, and we often find extensive injuries to our plants produced by this class of agents. When these are of a chemical nature, as is usually the case, they may be satisfactorily treated by applications that will neutralize their effects. In cities the escape of the illuminating gas, that is carried in subterranean pipes, has often so poisoned the soil as to destroy the shade trees by the side of the streets.

An excess of certain saline and alkaline ingredients often produces barrenness in the soil, by a sort of poisoning, even with those articles that in smaller quantities are used as manures with the happiest effects.

3d—The influence exerted upon vegetation by the growth of parasitic plants, cannot be observed without forcing us to the conclusion that they are prejudicial to the health of the plants they infest—since they either cover and smother the foliage by twining upon it, as is the case with the Dodder; or fasten themselves upon a limb, appropriating the sap that was intended for its support, and thus starve it, as does the Mistletoe; or attaching themselves to the bark, they interfere with its functions, as is done by the lichens and mosses; or, following the descending scale, in the size of these parasites, but meeting in them foes of much greater importance, we find the minute but innumerable fungi attacking the wood, the bark, the foliage, and the fruits, of our gardens and orchards, and committing incalculable damage—thus entailing serious disease. A very important question has arisen, however, as to whether the inroads of fungi were the cause or the consequence only of disease. A question which it will be necessary to leave to wiser heads, only observing that these epiphytes do appear, under certain atmospheric conditions, to invade some plants that had previously seemed to be in perfect health. That they are transported upon the air, in the form of very minute sporules, is unquestioned, and that their growth is dependent upon certain atmospheric conditions, is equally admitted, but whether they induce disease, or are only able to take possession of a plant that is not in a perfectly healthy condition, does not yet appear so clear. The very eminent Mr. Solly is of the opinion, that in the potato at least, the existence of parasitic fungi is a secondary result of previous disease. So it may be with our fruits, and there is considerable testimony to favor such a belief in many cases, where we find, with the appearance of these fungi, other causes of unhealthiness.