COMMISSIONER OF AGRICULTURE
THE YEAR 1862.
Government Printing Office
Among the many subjects of interest to the fruit-grower there are none that so imperatively demand his attention as those of shelter and protection to his crops; certainly there are none that
present a greater prospect of increased remuneration in the products of the orchard and garden.
It cannot have escaped the notice of those who are familiar with foreign works on horticulture, that their principal gardens and fruit gardens are surrounded by walls or hedges, showing that protection is deemed essential, or absolutely necessary to secure the best products by rendering the climate more congenial, and approaching more nearly the atmospheric conditions of warmer latitudes.
Allowing that the American climate, at least over the greater portion of the continent, is particularly favorable to the production of fruits, we cannot shut our eyes to the fact that in sheltered city gardens, vegetation commences at an earlier period, and, as a consequence, fruits ripen earlier, and in many instances attain a greater degree of perfection, and are less liable to casualties and diseases, than those in more open exposures; and those of a somewhat tender nature, as the fig and exotic grape, will flourish and fruit when thus protected while in contiguous open localities they would be killed to the root every winter.
It has become a standard remark of late that many of our best fruit trees are more liable to disease, and their products more generally inferior, both as to quantity and quality, than they formerly were. Admitting as a fact that much of this inferiority is owing to the increased age of orchards, as well as negligent culture, it cannot be denied that, even with improved knowledge in culture, many fruits are not produced in such perfection as formerly, under what would now be very properly termed unskilled labor.
Throughout most of the older cultivated regions of our country it is now of rare occurrence to find an orchard producing fruit not more or less imperfect. Apples are disfigured by warty and scab-like blotches, and pears are cracked and worthless. Blights, so called, are also more frequently met, and their origin as little understood as it was fifty years ago. We are fully aware of the prevailing tendency of some to applaud the past and decry the present. We can, also, give full allowance for the sympathetic associations of youthful times, when all seemed fair to our eyes, and when "stolen waters were sweet, and bread eaten in secret pleasant," and quarrel not with those who cannot see in our Bartletts and Belle Lucratives any such excellence as characterized the early Catharines of boyhood. Making due allowance for all of this, we are still convinced that both diseases and destructive insects are on the increase, and that the time has arrived in all its fullness when cultivators must possess themselves of all attainable knowledge relative to the principles of vegetable growth, and endeavor to deduce from such knowledge a course of practice applicable to their locality and the various crops they cultivate.
When agricultural chemists first proposed to instruct us, and point the more practical operator to the proper mode of culture, high promises of valuable aid were given, and the cultivators were induced to place confidence in the promises so lavishly bestowed. The conviction is, however, gradually becoming more settled that these promises are not being fulfilled. This was not unforeseen by intelligent, practical operators as it was evident that the multifarious agents of vegetation, and their still further, ramified combinations, could not be confined to the laboratory of the chemist; more particularly would be physical agents, air, light, heat, and moisture, be excluded from his investigations, or, at most, be but casually considered in his analytical labors. For example, in the amount of its ingredients, be he cannot so readily explain the exact specific relation between these raw ingredients and their preparation as food acids and alkalies, and is thus enabled to separate and value the substances of which the soil is composed; but this knowledge alone will not justify him in pronouncing upon the adaptability of that soil to produce a crop, for it has been repeatedly shown that a soil may possess an abundance of all the substances required by a crop, and yet be unproductive, for the reason that these elementary substances, although present, may not be in a sufficiently soluble condition to be available for the purposes of vegetation.
The constituent parts of a plant may, also, be very accurately determined; but how they are obtained, eliminated, held together, and assimilated by the plant, is another branch of study, as it is also the most important. Those who form theories and base their deductions upon investigations confined to the simple changes of dead matter will find so many opposing influences when life is concerned, as will compel them to a further study more intimately connected with vegetable physiology, and the important part that organic agencies exercise in the growth of plants, and the physical condition rather than the chemical constitution of the soil upon which they grow.
In the culture of plants the great aim should undoubtedly be to properly balance the agencies of growth; this is the great art of culture. Aware of the unlimited ramifications of this subject, it is not proposed to enter upon it at present, further than slightly glance at the importance of shelter as an auxiliary towards securing a desirable equilibrium of some of these agencies.
In brief, it may be stated that the necessities of shelter are two-fold— to guard against excessive aridity during summer and severe cold during winter. In other words, to modify the debilitating effects of the injurious evaporation produced by the extremes of heat and cold.
The debilitating effect upon vegetation of continued aridity during summer is well known, and various expedients are resorted to, in order to ameliorate its influence, and it is found that one of the most effective, and at the same time most available means of checking evaporation is by arresting the currents shelters of vegetation. Our natural forests are rapidly being destroyed, and it is admitted that the destruction of forests tends to lesson [sic] the moisture both of the atmosphere and the soil. The disappearance of the streams in the mountains of Greece, and the sultry atmosphere and droughts of the Cape de Verd islands, have been attributed to the destruction of the forests. In densely wooded countries, where in connexion with excessive rains, the climate is rendered unhealthy, clearing the lands of vegetation has been the means of vast improvement, as we are told has been experienced at Rio de Janeiro. Hence it is reasonable to suppose that by planting belts and groups, in masses of hardy, suitable trees, in the vicinity of orchards and gardens, the dry currents will be arrested, and injurious exhalations from the crops measurably prevented; and, further, it may be found that atmospheric moisture will be increased by the proximity of such masses of trees from the results of condensation on their surfaces. That exhalation is much diminished when the drying current is arrested, and increased with the rapidity of the arid breeze, is well known, and the formula has been given that the same surface which, in a calm state of the air, would exhale one hundred parts of moisture, would yield one hundred and twenty five in a moderate breeze, and one hundred and fifty in a high wind; the beneficial effects of arresting or diminishing the force of currents is, therefore, very evident.
So little are we acquainted with the diseases of plants, that no intelligent classification of them has been attempted. The terms mildew and blight are used in a general sense to indicate the results of disorganization; but the causes that produce these results are not so readily distinguished.
Mildew, in some one or other of its forms, has become one of the greatest evils connected with fruit culture. The mildew on the native and foreign grape, on the gooseberry, the cracking and scabbing of the pear and the apple, are well known causes of perplexity to cultivators; and, although the formation and increase of mildew is not particularly well understood, and while it is, perhaps, premature to advance the opinion that it is wholly the result of atmospheric disturbances, and capable of being prevented by suitable shelters, there is accumulating evidence showing that position and exposure are closely connected with its appearance and exemption.
For the successful adornment of lawns and pleasure grounds, shelter is of the first importance. One of the greatest obstacles to the growth of choice evergreen trees and shrubs, especially during the earlier stages of growth, is the aridity of our summers. Broad-leaved evergreens, as the Mahonia, the Rhododendron, and others of similar character, must be sheltered and protected if they are expected to grow into objects of beauty or interest. In their native habitat these plants are protected by superior vegetation, and surrounded with an atmosphere more uniformly charged with moisture than they usually are in artificial plantations.
Protection during winter is not less an object of utility. The degree of cold that plants will resist uninjured is a question that cannot be definitely answered; a plant will occasionally be destroyed by a degree of cold that it previously encountered without apparent injury. We are not to suppose, in cases of this kind, that they proceed from changes in the laws of nature, but rather that the resisting power, by some means or other, has been reduced, or, what is more probable, that the mere thermometric degree of cold is not the main cause of injury.
Future investigations may determine that many of the diseases of plants originate from the effects of cold and its accompaniments during winter. There is no reason why fatal influences may not linger in vegetable as well as in animal organism, and our experience and observation has led to the conviction that such instances are by no means rare.
According to the theories of De Candolle, the power of plants to resist extremes of temperature is—
1. In the inverse ratio of the quantity of water which they contain.
2. In proportion to the viscidity of their fluids.
3. In the inverse ratio of the rapidity with which their fluids circulate.
4. In proportion to the size of the cells, so is the liability of plants to freeze.
5. The power of plants to resist the extremes of temperature is in exact proportion to the amount of confined air which the structure of the plants themselves enables them to contain.
Whatever degree of truth these theories may contain, there is not much calculated to materially assist the ordinary cultivator. He cannot ascertain the dimensions of the cells, neither can he measure the quantity nor decide upon the quality of their fluids; external appearances will not contribute to his aid, for, while the oak and the orange are undeniably of solid texture, the one is hardy and the other is not; the wood of the fig is similar in texture to that of the willow; but while the first is susceptible of injury from slight frost, the willow will stand unharmed through our most severe winters.
The exact process by which cold destroys plants is a matter on which there is room for much conjecture. The mechanical action due to the expansion of fluids while freezing, in lacerating and disrupting their tissue and thereby destroying the connexion of the sap vessels, has been deemed a sufficient explanation. We cannot, however, consider it a conclusive reason for all the phenomenon for all the phenomena observed when plants are frozen. The disruption of tissue and fluid produced from this cause; but, as has already been remarked, plants may at times be subjected to a severity of cold that solidifies the sap, and yet remain perfect and healthy, while they will succumb to comparatively slight cold, if long continued and accompanied by rapidity in the currents of air.
When green-house or other tender plants are accidentally frozen, they may be resuscitated by carefully shading them from the sun, sprinkling them with water, and surrounding them with a moist atmosphere, continuing these conditions until the temperature is increased to a safe point. We have repeatedly tried the experiment of removing a plant thus frozen into a house, where it was placed under the influence of a dry heat and exposed to the sun while in the frozen state, and the experiment proved fatal to the plant. This mode of treating greenhouse plants, when accidentally exposed to a few degrees of frost, is a common and successful expedient. We have seen eight degrees of frost suddenly obtain in a a greenhouse containing a varied collection of plants, many of them of a very tender nature, and so completely frozen that many of the branches and succulent shoots were rendered as brittle, and broke as easily as a delicate rod of glass; yet by prompt and effectual shading, and increasing the moisture and temperature slowly, very few were injured. It is difficult to conceive how plants so circumstanced could escape destruction if their tissue is disrupted when the sap which they contain is converted into ice, since no after treatment could then save them, as no process, either slow or rapid, could reconstruct the tissue.
Whatever may be the injury from disruption, we are convinced that extreme cold and extreme heat act in a similar manner upon plants, and that exhaustive evaporation is equally injurious, whether produced by one or other of these extremes; and although physiologists have not been able to give any well-defined explanation why one plant is hardier than another, further than that its constitution is adapted to its natural climate, it is well known that plants are rendered more capable of resisting extremes when their wood has attained its greatest degree of maturity. This also coincides with the opinion of De Candolle; his first, second, and third axioma prove that plants resist frost in proportion to the solidity of their wood.
Perfect maturity of growth is the great object of all cultivation; this fact should always be uppermost in the mind of the fruit-grower. Too much importance cannot be placed on the fundamental principle, in fruit culture, that whatever tends to render tissue moist, increases its susceptibility to injury from cold, and whatever tends to reduce humidity, and hasten the conversion of fluid-matter into woody fibre, increases its power of resisting cold; but this is not the only result of thorough maturity, for without it there can be no fruit. The failures in fruit-culture arising from excessive luxuriance, and stimulated growths that never mature, are beyond calculation. The production of mere wood growth and the production of fruit are antagonistic processes; and until this fact is recognized and acted upon the highest excellence of culture will not be attained.
With regard to the hardihood of plants and the necessities of protection, there are individuals who maintain that a fruit tree or plant to be valuable, or fitted for general culture, must be able to take care of itself. This cannot be looked upon in any other light than as a lame excuse for indolence and neglect. It is the province of man to assist nature in producing such results as he finds most desirable for his purposes; and if he removes plants from their natural conditions, and then leaves them to take care of themselves, he must expect to realize the usual consequences of neglect.
The object of these remarks may be rendered more apparent by a brief enumeration of some of the more important advantages which may be expected from partial shelter and protection, and through them the exemption from, or modification of diseases of various kinds on some of the most valuable fruit trees and plants.
The cracking of the apple and the blotches and scarifications frequently observed on its surface have been referred to the attack of fungoid growths or mildew. Various examples have been cited where orchards, sheltered from prevailing winds, have shown a decided exemption from these attacks. In opposition to this supposed cause of immunity it has been asked, Are our orchards more exposed now than they formerly were? As a general rule, we think it quite likely that they are, seeing that in all sections as cultivation increases the forests are gradually thinned and cleared. The effects of destroying the forests of a country have already been noted; and we have a partial recognition of the importance of shelter in the precept of many intelligent orchardists who advocate the planting of fruit trees much closer than has formerly been the rule, and also in the practice of encouraging the trees to branch quite to the surface, instead of training to a clear stem five or six feet from the roots. Both these expedients have a tendency to prevent rapid circulation of air through the orchard, and consequently are so far a preventive against evaporation from the soil as well as from the surfaces of the trees. Examples are not yet sufficiently numerous to warrant a decided opinion; but so far as they have been noted, the prospect of greater immunity by this mode of treatment is encouraging.
The cracking of this fruit has given rise to much speculation, and various theories have been advanced with reference to the cause. For a long period the opinion prevailed that it was owing to a deficiency of certain mineral ingredients in the soil, and various remedies based on this assumption were freely dispensed and tried, but with indifferent success. It is not now doubted that it is the result of mildew [later, the culprit fungus was more precisely identified as pear scab. -ASC], and that the atmosphere, and not the soil, is at fault. In support of the opinion that it is governed by atmospheric influences, the fact may be quoted that the White Doyenne, one of the finest pear when perfect, rarely succeeds in exposed localities; yet, when grown in positions thoroughly protected, it is still produced in all its pristine beauty and excellence. Referring to cases with which we are familiar, we have seen annual exhibitions of this fruit grown in the built-up portions of the cities of Philadelphia and Baltimore, most perfect of its kind, without spot or blemish, when those from trees growing in the more exposed suburbs invariably proved defective. Again, it has been lately shown that, fruited in the quiet atmosphere of a fruit-house, they attain great perfection; and further, we have seen a tree, one of a row that produced worthless fruit, enclosed on all sides by a small box, open at top and elevated a few inches above the soil, produce perfect fruit, while the productions of the adjoining trees were, as usual, cracked and worthless. Whatever may be allowed for protection in the above cases, it is very evident that they were not influenced by the nature of the soil.
The origin of the blight on the pear tree has also been a fruitful source of conjecture. No doubt the term is applied to effects
produced from various causes. We will state our observations on one species of this malady or disease. Those who have pear orchards will, perhaps,
recall instances where the trees, or portions of them, have suddenly ceased to grow shortly after budding in spring.
The young leaves and growths present a blackened appearance and rapidly wither. On examination, the bark will present a shrivelled appearance,
and on cutting into the wood it is found discolored and apparently in a state of decomposition. In some instances a solitary limb, but more usually one side of the tree,
will be more particularly affected. By cutting down until all discolored wood is removed, the plant will recover; but if neglected, the entire plant will be destroyed.
Having lost many trees in this manner, and observing that it was most prevalent after severe winters,
especially if the ground was frozen fourteen or sixteen inches during February and the early portion of March,
it occurred to me that it was induced from evaporation at a time when the plants were unable to absorb by by the roots. When the soil is frozen to a depth of sixteen inches it is evident
that all roots within that depth must also be frozen, and absorption and circulation be completely arrested. While the roots are in this state the branches are subject to the drying air
of spring, and their juices are exhausted by evaporation; the supply of moisture by the roots being inert, the plant has no more power of supporting life than it would have supposing it to be cut
over at the surface and thrown on the ground. These conditions, long continued, must result in injury; and if not immediately destructive, disease is engendered,
to be intensified by the first untoward influence.
[This theory is now disproven and if one thinks about it, the theory makes little sense. For instance, in the Southeastern U.S., the ground is never frozen to this depth in February and March (actually not in any month in much of the South), yet this part of the country has the worst fireblight pressure on the continent. Fireblight is caused by a bacterium, Erwinia amylovora, and warm, wet weather, especially during blooming and hailstorms, especially in the spring and early summer are the conditions that facilitate blight epiphytotics. -ASC
It is not to be supposed that this is the sole cause of blights, but I am convinced that it is a frequent one, and more prevalent on what are termed dwarf pears, the root of which being quince, do not reach so deep as the pear roots, but rather ramify and spread nearer the surface, and therefore are more likely to be included in the frozen strata. [Quince is also genetically susceptible to blight, at least as much as the more-susceptible pear stocks used at the time. -ASC] Supposing that this was a source of blight, I adopted the practice of covering over the roots in early winter with charcoal dust, a few inches in depth of which will entirely prevent the penetration of frost. [Wood ash (charcoal dust) is rich in potassium, which has been shown to reduce the severity of blight. -ASC] Since this precaution has been adopted, I have not observed even a blighted limb or leaf. [Where was his orchard? How many years of observation is this assertion based upon? How effective would this practice be in other locations? My guess would be, not very effective. -ASC] I think it cannot be shown that the roots of plants are in any degree benefited by being frozen, and it can certainly be shown that they are oftentimes injured by it. Therefore it is a safe rule to protect the roots so that their absorbing powers may constantly be ready for action.
It may be well to note, in connexion with this subject, that crops, both of apples and pears, are sometimes lost b late frosts when they are in bloom. It is an old custom, but now much neglected, to have ready, in various suitable localities around an orchard, several heaps of dried weeds or rubbish of such description; then should a slight frost occur when the trees are in bloom, set fire to these heaps and endeavor to create as much smoke as possible. Crops have repeatedly been saved by this precaution. It is obvious that these smoking heaps should be placed on the windy side.
The curl, or leaf blister of the peach, although seldom fatal in its effects,