Part 3

When these winds finally cease, the atmosphere has a low relative humidity, not enough moisture remains in the air to prevent radiation; the heat absorbed by the earth through the day is, during the bright, cloudless night, rapidly radiated and lost in space, and a reduction in temperature of twenty to thirty degrees is the consequence.

In the first place, the potato-vines suffer by excessive exhalation; in the second, by sudden reduction of temperature, and, though not frozen, their functions are much deranged, and their vitality greatly enfeebled. To use a common expression, the plant "has caught a violent cold that has settled on the lungs."

The leaves (which are the lungs of plants) now fail to perform their functions properly. The points of many of the leaves turn brown, curl up, and die.

The ascending sap, not being fully elaborated by the diseased leaves, oozes out through the skin of the stalk in a thick, viscous state, and the plant to all appearance is in a state of consumption.

At this stage the ever-present minute spores of the _Botrytis infestans_ eagerly pounce on the sickly plant, fastening themselves on its most diseased parts. The _Botrytis infestans_ is a cryptogamous plant, and is included in the Mucidineous family, (moulds.) It is a vegetable parasite preying upon the living potato plant, like lice or other animal parasites upon the animal species.

At first this mould forms webby, creeping filaments, known in botanical language as mycelium. These root-like fibres then branch out, sending out straight or decumbent articulated stems. These bead-like joints fill up successively with seeds or spores, which are discharged at the proper time to multiply the species.

Under favorable conditions of warmth and moisture, the mycelium spreads very rapidly. Spores are soon formed and matured, to be carried to plants not yet infected. Rains also wash the seminal dust down the plant, causing it to fasten and grow on the vine near the ground. The roots of the parasite penetrate and split up the stalk even to the medullary canal.

These roots exude a poisonous substance, which is carried by the elaborated descending sap down to the tubers, and as the largest tubers require the largest amount of elaborated sap for their development, they will, consequently, receive the greatest quantity of the vitiating principle, and will, on digging, be found a mass of rottenness, when the smaller ones are often but slightly affected. The _Botrytis infestans_ can not gain a lodgment on vines that are truly healthy and vigorous, high authority to the contrary notwithstanding.

Healthy varieties, growing in a sheltered situation on dry, new soil, to which no nitrogenous manures have been applied, can not be infected, though brushed with other vines covered with the fungus. Different varieties, and sometimes different members of the same variety, are not always alike affected by the disease, though growing in the same hill.

As will be noticed, the potato disease is rather an effect than a cause, and appears to have been designed to prevent members enfeebled by accident or otherwise from propagating their species by putting such members out of existence. Ozone, supposed to be a peculiar form of oxygen, is exhaled from every part of the green surface of plants in health, and effectually repels the attacks of mildew; but it is found that when the atmosphere is very dry, or, on the other hand, very humid, plants cease to evolve ozone, and are therefore unprotected. Winds from the ocean are strongly ozonic, and it is ascertained that plants growing on soil to which salt has been applied evolve more ozone than others. Hence the benefit derived from the use of salt on potato lands.

The "Black knot," another species of fungus that attacks the branches of the plum and Morello cherry, operates very similarly to the potato mildew. The roots of the parasite penetrate and split up the cellular tissue of the branch on which it fastens, and if the limb be not promptly amputated, the descending sap carries the deleterious principle through the whole system, and the following year the disease appears in a greatly aggravated form in every part of the whole tree. The remedy in this case is prompt amputation of the part diseased on its first appearance, and a judicious application of salt to the soil.

Common salt, to a certain extent, is as beneficial to some plants as to animals; and every intelligent farmer knows that if salt be withheld from the bovine _genus_ for any considerable length of time, the general health droops and parasites are sure to abound. The object of nature in bringing into existence the large family of mildews, each member of which is a perfect plant in its way, and as capable of performing its functions as the oak of the forest, was undoubtedly to prevent propagation from sickly stock, and by the decomposition of feeble plants to make room and enrich the soil for the better development of healthier plants. But it by no means follows that, because a plant is attacked by mildew, it must necessarily be left to die, any more than it follows that, because an animal is infested with vermin, it should be let alone to be eaten up by them.

REMEDY FOR THE POTATO-ROT.

In treating for the potato-rot, "an ounce of prevention is worth a pound of cure;" for when leaves or vines are once dead, they ever remain so. All that can be done for potatoes infested is to stop the mildew from spreading, by destroying it where it is, and by strengthening "those things which remain." The writer was led to the adoption of the remedy proposed by experiments made upon fruits.

Every one who has an apple or pear-orchard must have observed that mildew of fruit supervenes after some sudden change of temperature, especially when accompanied by rain. Spots of mildew invariably form on the young fruit immediately after a cold night, when the thermometer has indicated a change of twenty to twenty-five degrees. This growth of mildew takes place when the apples are of various sizes, from the earliest formation to the size of large marbles. These fungous growths appear as dark-colored spots, which arrest the growth of the apple immediately beneath, causing it to become distorted, while the expansion and contraction bring on diseased action, which results in the cracking and general scabbiness of the fruit.

Knowing that dry-rot (_Merulius Lachrymans_, Schum,) another species of fungus, was remedied by an application of sulphuric acid, I thought it might possibly destroy the fruit mildew. An application of plaster, (gypsum,) which is composed of lime and sulphuric acid, was made with the happiest results. It was found that an apple dusted with ground plaster at its first formation remained free from mildew and came to maturity, while apples growing by it, but not so treated, became scabby and worthless. It was also ascertained that a thorough application of plaster destroyed the mildew after it had formed, and that such fruit came to maturity. On the potato mildew, so far as the writer's experience extends, plaster, if applied early, is a perfect prevention, and if not delayed too long after the disease appears, is a certain remedy.

The vines should be watched closely, and on the first appearance of the disease plaster should be applied; not merely sowing it broadcast, but dashing it over and under the vines, bringing it in contact with the stalks, using a handful to three or four hills. Plaster for this purpose should be very dry and powdery, and should be applied when the air is still. One application is seldom sufficient; it should be renewed as often as circumstances require. Examine the vines about three days after a cold night, or about the same length of time after a heavy rain. If the leaves begin to curl and wither, apply plaster at once; and, in short, whenever the vines show any signs of drooping, be the cause bites of insects, excessive aridity, or excessive humidity of the atmosphere, or sudden change of temperature, drooping from any cause whatever indicates the approach of mildew, which should be promptly met with an application of plaster. As before stated, plaster the vines as soon as they are up, again after the last plowing and hoeing; after that, one, two, or three times, as circumstances indicate.

By this method the vines are kept of a bright lively green, and the tubers are kept swelling until growth is stopped by frost. Another point gained is, potatoes so grown are so sound and free from disease as to be easily kept for spring market without loss by rot.

Whether the surprising effects of plaster on the potato mildew is attributable to the sulphuric acid, to the lime, or to its simply being a dust, has not been determined. It is well known that the fruits of a vineyard or orchard in close proximity to a dusty and much frequented highway are remarkably free from mildew, which can only be due to dust settling on the trees and fruit. But in the case of plaster, the writer is inclined to believe its efficacy is mainly due to the sulphuric acid, probably assisted by the lime in a state of dust. Be this as it may, it matters not. The result is all that can be desired; the remedy is easily applied, costs but a trifle, and a single season's trial is all that is needed to convince the most skeptical grower of its merits.

DIGGING AND STORING

Is full half the labor of growing and securing a crop of potatoes. Digging is a long, laborious task. Many small fortunes are sunk yearly by inventors in experimenting with and constructing "potato-diggers;" but, so far, no machine has done the work properly except under the most favorable circumstances. Stones, vines, and weeds are obstacles not yet fully overcome. Many tubers are left covered with earth, and so lost; and besides, some machines so bruise the potatoes in digging as to injure their appearance and keeping qualities. Undoubtedly, the day will come when the great bulk of potatoes will be dug well and rapidly by horse-power; but until that day does come, the potato-hook must be used.

Much of the back-ache and general unpleasantness incident to digging is avoided, or greatly mitigated, by having the potatoes large and sound, turning out a peck to the hill, especially if the digger is the owner of the crop.

Digging should be done only when the ground is dry, that the potatoes may come out clean and bright. A small plow, to turn a light furrow from each side of the rows, is some help. Pull up the vines, and lay them down so that they will be covered by the dirt dug from the hill. Commence on one side of the hill; press the hook or hoe down, so that it will reach a trifle below the potatoes, and draw the implement firmly toward you. Repeat the operation, each time placing the tool a few inches further in or across the hill, until the whole hill is dug. By this method the potatoes will not be bruised; whereas, if the digging be commenced in the centre of the hill, many potatoes will be sacrificed and much injured. Potatoes should be picked up as soon and as fast as dug; and immediately covered with straw or other material, to protect them from the light. A few hours' strong sunshine will ruin the best potato ever grown. Light changes the natural color to green, and renders the potato so bitter and unpalatable as to be wholly unfit to eat.

Owing to the inconsiderate way in which potatoes are often dug, and the light to which they are exposed while being transported to and while in market, the denizens of our cities seldom, if ever, taste this vegetable in its greatest excellence. If to be stored in the cellar, the potatoes should be left in the field, in heaps covered with straw, until the sweating is over, and then be removed to the cellar and lightly covered with dry sand, or earth, just sufficient to exclude the light.

If to be buried in the field, choose a dry, sideling place; scrape out a slight hollow, by merely removing the surface soil with a hoe; into this, pile ten to twelve bushels; place the potatoes properly, and cover them carefully with clean straw, six inches deep; cover over the straw with four or five inches of earth, except a small opening at the top; over this opening place a board or flat stone, elevated a little on one side, to lead off the rain.

Let them remain so until the sweating is completely over, or so long as prudence will permit; and when cold weather fairly sets in, add more earth to keep from freezing, leaving only a wisp of straw protruding through to carry off any foul air that may be generated.

Where the winters are intensely cold, it is best to cover but lightly with earth, say five or six inches deep; and when freezing is becoming severe, spread over the heap buckwheat straw, or coarse manure, to the depth of six inches. There is danger in covering very deep at first, especially if the autumn should prove warm. If kept too warm, rot is sure to ensue. Experience shows that any vegetable keeps better buried in pits that contain not more than ten or twelve bushels each.

Where large quantities are to be buried, it is advisable to open a long, shallow, broad trench, leading up and down a hill, if possible, to secure good drainage. Commence, at either end, by placing a desirable quantity of potatoes as soon as dug; next to these put a little straw; against the straw place about six inches of earth; then more straw and more potatoes; and so keep on until the trench is full. A few furrows plowed on each side assist in covering; and make a drain to lead off the rains, which is a matter of the first importance. By this method each lot of potatoes is kept separate; and any section can be opened at any time to be taken to market, without endangering the others.

Potatoes buried properly are usually of better flavor in the spring than it is possible for potatoes to be which are kept in a common cellar.

And here let me add that, if leaves from the woods be used instead of straw, to cover potatoes to be buried, such potatoes will be of better flavor; and further, if nothing but dry earth comes in contact with them, they will be better still. Straw is used for the twofold purpose of securing an air-chamber to keep out frost, and to prevent the earth from mingling with the tubers on opening the pits.

INSECTS INJURIOUS TO THE POTATO.

There are ten distinct species of insects preying upon the potato-plant within the limits of the United States. Many of these ten species are confined within certain geographical limits. Their habits and history differ very widely. Some attack the potato both in the larva state and in the perfect or winged state; others in the perfect or winged state alone; and others again in the larva state alone.

In the case of seven of these insects, there is but one single brood every year; while of the remaining three there are every year from two to three broods, each of them generated by females belonging to preceding broods. Eight of the ten feed externally on the leaves and tender stems of the potato; while two of them burrow, like a borer, exclusively in the larger stalks.

Each of these ten species has its peculiar insect enemies; and a mode of attack which will prove very successful against some of them will often turn out to be worthless when employed against the remainder.

~The Stalk-Borer~,[A] (_Gortyna nitela_, Guenee.)--This larva (Fig. 2,) commonly burrows in the large stalks of the potato. It occurs also in the stalks of the tomato, in those of the dahlia and aster, and other garden flowers. It is sometimes found boring through the cob of growing Indian corn. It is particularly partial to the stem of the common cocklebur, (_Zanthium sirumarium_;) and if it would only confine itself to such noxious weeds, it might be considered more of a friend than an enemy. It is yearly becoming more numerous and more destructive. It is found over a great extent of country; and is particularly numerous in the valley of the Mississippi north of the Ohio River. The larva of the stalk-borer moth leaves the stalk in which it burrowed about the latter part of July, and descends a little below the surface of the earth, where in about three days it changes into the pupa, or chrysalis state.

[Footnote A: Where no hair-lines are given, the insects are represented life-size.]

The winged insect (Fig. 1,) which belongs to the same extensive group of moths (_Noctua_ family, or owlet moths) to which all the cut-worm moths appertain, emerges from under ground from the end of August to the middle of September. Hence it is evident that some few, at all events, of the female moths must live through the winter, in obscure places, to lay eggs upon the plants they infest the following spring; for otherwise, as there is no young potato, or other plants, for them to lay eggs upon in the autumn, the whole breed would die out in a single year. This insect, in sections where it is numerous, does more injury to the potato crop than is generally supposed.

~The Potato-Stalk Weevil,~ (_Baridius trinotatus_, Say.)--This insect is more particularly a southern species, occurring abundantly in the Middle States, and in the southern parts of Missouri, Illinois, and Indiana. It appears to be totally unknown in New-England.

The female of this beetle deposits a single egg in an oblong slit, about one eighth of an inch long, which it has previously formed with its beak in the stalk of the potato. The larva subsequently hatches out, and bores into the heart of the stalk, always proceeding downward toward the root. When full grown, it is a little more than one fourth of an inch in length, and is a soft, whitish, legless grub, with a scaly head. Hence it can always be readily distinguished from the larva of the stalk-borer, which has invariably sixteen legs, no matter how small it may be. Unlike this last insect, it becomes a pupa in the interior of the potato-stalk which it inhabits: and it comes out in the beetle state about the last of August or beginning of September.

The stalk inhabited by the larva wilts and dies. The perfect beetle, like many other snout-beetles, must of course live through the winter, to reproduce its species the following spring. In Southern Pennsylvania, some years, nearly every stalk of extensive fields is infested by this insect, causing the premature decay of the vines, and giving them the appearance of having been scalded. In some districts of Illinois, the potato crop has, in some seasons, been utterly ruined by this snout-beetle, many vines having a dozen larvæ in them. This insect attacks no plant but the potato.

~The Potato-Worm~, (_Sphinx 5-maculata_, Haworth.)--This well-known insect, the larva of which (Fig. 3,) is usually called the potato-worm, is more common on the closely allied tomato, the leaves of which it often clears off very completely in particular spots in a single night. When full-fed, which is usually about the last of August, the potato-worm burrows under the ground, and shortly afterward transforms into the pupa state, (Fig. 5.) The pupa is often dug up in the spring from the ground where tomatoes or potatoes were grown in the preceding season, and most persons that meet with it suppose that the singular jug-handled appendage at one end of it is its _tail_. In reality, however, it is the _tongue-case_, and contains the long, pliable tongue which the future moth will employ in lapping the nectar of flowers. The moth itself (Fig. 4) was formerly confounded with the tobacco-worm moth, (_Sphinx Carolina_, Linnæus,) which it very closely resembles, having the same series of orange-colored spots on each side of the abdomen.

The gray and black markings, however, of the wings differ perceptibly in the two species; and in the tobacco-worm moth there is always a more or less faint white spat, or a dot, near the centre of the front wing, which is never met with in the other species. The potato-worm often feeds on the leaves of the tobacco plant in the Northern States. In the Southern States, in Mexico and the West-Indies, the true potato-worm is unknown, and it is the tobacco-worm that the tobacco-grower has to fight. The potato-worm, however, is never known to injure the potato crop to any serious extent.

~The Striped Blister-Beetle~, (_Lytta vittata_, Fabr.) This insect (Fig. 6) is almost exclusively a southern species, occurring in some years very abundantly on the potato-vines in Southern Illinois, and also in Missouri, and according to Dr. Harris, it is occasionally found even in New-England. In some specimens the broad outer black stripe on the wing-cases is divided lengthwise by a slender yellow line, so that, instead of _two_, there are _three_ black stripes on each wing-case; and often in the same field may be noticed all the intermediate grades; thus proving that the four-striped individuals do not form a distinct species, as was supposed by the European entomologist Fabricius, but are mere varieties of the same species to which the sixth-striped individual appertains.

The striped blister-beetle lives under ground and feeds upon various roots during the larva state, and emerges to attack the foliage of the potato only when it has passed into the perfect or beetle state.

This insect, in common with our other blister-beetles, has the same properties as the imported Spanish fly, and any of them will raise just as good a blister as that does, and are equally poisonous when taken internally in large doses. Where the striped blister-beetle is numerous, it is a great pest and very destructive to the potato crop. It eats the leaves so full of holes that the plant finally dies from loss of sap and the want of sufficient leaves to elaborate its juices. In some places they are driven off the plants (with bushes) on a pile of hay or straw, and burned. Some have been successful in ridding their fields of them by placing straw or hay between the rows of potatoes, and then setting it on fire. The insects, it is said, by this means are nearly all destroyed, and the straw burning very quickly, does not injure the vines.

~The Ash-Gray Blister-Beetle~, (_Lytta cinera_, Fabr.)--This species (Fig. 7, male) is the one commonly found in the more northerly parts of the Northern States, where it usually takes the place of the striped blister-beetle before mentioned. It is of a uniform ash-gray color. It attacks not only the potato-vines but also the honey locusts, and especially the Windsor bean. In particular years it has been known, in conjunction with the rose-bug, (_Macrodactylus subspinosus_, Linn.,) to swarm upon every apple-tree in some orchards in Illinois, not only eating the foliage, but gnawing into the young apples.

This beetle does considerable damage to the potato crop, especially in the North-Western States. Like the other members of the (_Lytta_) family, it lives under ground while in the larva state, and is troublesome only when in the perfect or winged state.

~The Black-Rat Blister-Beetle~, (_Lytta murina_, Le Conte.)--This species (Fig. 8,) is entirely black. There is a very similar species, the black blister-beetle, (_Lytta atrata_, Fabr.,) from which the black-rat blister-beetle is distinguishable only by having four raised lines placed lengthwise upon each wing-case, and by the two first joints of the antennæ being greatly dilated and lengthened in the males, of the lath species. It is asserted by some authors that the black blister-beetle is injurious to the potato; but I can not see how it could do much damage to that crop, as the perfect insect does not appear until late in August, when the potato crop is nearly out of its reach. Not so, however, with the black-rat blister-beetle, which is on hand ready for business early in the season. This insect does considerable damage to the potato in Iowa, and neighboring States; it is also found, though in not so great numbers, throughout the whole of the Northern States.