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Plant And Animal Diseases

( Originally Published 1915 )

The Microscope Reveals a Wonderful World.—The world seen by the naked eye is beautiful and wonderfully varied ; but there is another world equally beautiful and varied, a world that means life or death, success or failure; a world so subtle and complex that the most learned scientists make no claim to more than a partial understanding of it. And yet what a blessing is that little which they have learned. Plagues, diphtheria, blights, tuberculosis, smuts and kindred phenomena are not now looked upon as dread visitations of a wrathful God. We are slowly but surely beginning to obey that first command—" Have dominion over them." Diseases of plants and animals are coming under man's control. He is slowly learning that potato blight, grain rust, hog cholera, black-leg, soil bacteria, etc., are as much under his control as are water and weeds. Is it right that the country boys and girls, whose very existence depends upon a rational control of this wonderful bacterial and fungous world, shall grow up unconvinced of the existence of these bacteria and fungi because unable to see through a microscope? Is it right that a farmer be doomed to toil for years to no advantage because his teacher and his school failed to bring his mind into contact with this wonderfully interesting world ? The great corporations have skilled experts to study processes and to give their managers and workmen the results of that study, so that they may employ only the most approved methods of dealing with the bacteria en-countered in making canned products, leather, tobacco, wine, beer, pickles, and hundreds of other things known to modern commerce. The farmer, too, has his skilled experts in the State, the United States Department of Agriculture, and in the Experiment Stations. But to what purpose do these toilers labor if our schools fail to bring the mind into contact with these phenomena which influence life on every side ? Bulletins by the thousands are published at our expense and distributed free, but many of the most valuable ones cannot be read by one who has not had an introductory course in bacteria and fungi.

Teach by Use of Types.—Psychology teaches us that we do not need to study everything, but by becoming conscious of the typical from actual observation, or better, by care and culture, we may reason fairly well about other things. A child cannot learn in the public schools all moulds and bacteria, but he should learn something about typical ones. Our schools have no right to let pupils graduate who doubt the existence of disease germs. To see is to believe, therefore let them see.

Mildews and Moulds for Nature Study.—Probably one of the mildews or one of the moulds makes the best introduction to the study of the fungi. Let some child draw a tooth-pick or sliver over a piece of mouldy bread or fruit and then rub the tooth-pick across a piece of fresh moist bread. The tooth-pick should be drawn over the fresh piece so as to make a letter X or the child's initials. Then lay the piece of inoculated bread where it will keep moist and out of sunlight—under an inverted box, containing moist blotting paper, or a saucer with a little water in it will do very well. Remove the cover after two days and later observe from day to day what happens. Why do we have to keep it out of sunlight ? What does this suggest as to the control of diseases?

Professor Hodge recommends the following : " A jelly glass, or even a medicine vial, furnishes ample room for a garden of these instructive plants, and they can be cultivated on almost anything for soil. First we will take some kind of liquid culture medium, in which we can see all of the different parts of the plant as it grows. Fruit juice as it comes from preserves, as clear and as colorless as possible, diluted one-half and filtered or strained through fine cheese cloth, makes an ideal medium. Fill the glass or vial half full and sprinkle a little dust from the school-room over the surface. Cover and set aside to observe from day to day. Three such cultures should be made, one of which should be kept in a dark place, one in a room where direct sunlight does not fall upon it, and the third should be kept in the sunlight as much as possible." If the teacher thinks best, each pupil may have a vial and make his own culture, taking notes of just what he does and what results, Then questions may be asked to bring out why in canning we heat things to destroy spores and germs, and how we put on covers, etc.

Study the Downy Mildews.—If the season is wet and warm enough, a study should be made of one of the downy mildews. These attack a large variety of plants, such as lilac, grape, cucumbers, onions, beans, potato, peach, plum and other plants. The grape (see text in Botany for Plasmopara viticola), or the lilac (see Botany for Microsphaera alni) leaves are apt to be covered on the under side. The body part of the fungus called hypha is a thread or mass of threads winding its way around, through and among the cells of the leaves. Most of the hypha; grow between the cells of the leaf and send into the cells small bodies called haustoria. These haustoria suck the life from the leaf cell, to feed the hyphae of the mildew. These fungi do not have seeds but they produce little microscopic bodies generally spherical in form, which spread the plant from leaf to leaf. Somewhat similar spore-bearing bodies may be seen on the common bread mould. But the downy mildews produce their spores at the end of stalks which emerge from the breathing pores (stoma) on the under side of the leaves or else in little sacks which are pushed out through the tissue of the leaf. The little spores go off into the air like sparks from a Roman candle. The spores fall upon other leaves and there germinate and give rise to new hyphae.

The only way man can protect his plants is to have the leaves well covered with a very thin coat of Bordeaux mixture or lime-sulphur solution. This must be spread with a spray so as to be very finely divided and a thin film spread over the whole surface. There is no way to help a leaf once the hyphae have entered and are growing within the tissue.

Rusts—Wheat Rust.—Now by analogy we should be able to make plain the spread of the rusts. First of all, while some farmers may not believe it, the boys must be impressed with the fact that rusts are plants, that plants come from plants, that as the Good Book says, " Whatsoever a man soweth that shall he also reap." There are many rusts and it is a question whether each grows on more than one kind of plant or not. There are oat, wheat, bean, clover, timothy, stone fruit rusts and others. Wheat rust (see Botany for Puccinia graminis) is common and makes a good type study. Wheat rust exists in three forms, though it is believed that two forms on the wheat alone are sufficient to perpetuate the disease. During one stage the fungus lives on the leaves of the barberry. It emerges from the under side of the barberry leaf as a red rust ; that is, the spore-bearing bodies, instead of being white as we found them in the downy mildews, are red. From the barberry leaf the spores are wafted in the wind to the wheat, where they grow and cause blister-like bodies which break open and from which emerge either of two kinds of spore stalks. Some (the uredospores) are red; the others (teleutospores or winter spores) are black.

No satisfactory method for controlling this disease has been found. Part of the summer spores may be destroyed by burning the straw and part of the winter spores may be destroyed by burning the stubble, but by that method we lose the plant food and humus. Rotation of crops is of aid and favorable weather helps very much. This means rather cool, dry weather, for hot, wet weather is the most favorable weather for the rust. Wide rotation of crops helps but the spores are blown for miles in some seasons. The fallowing practised with the dry farming is beneficial both to preserve moisture and to help hold the rust in check. Macaroni wheat is not injured so seriously as are other varieties, and hence we may be able to breed a hybrid of the macaroni and some of our common wheats which will be immune to the rust.

At times it is necessary for a farmer to stop growing certain kinds of plants for a series of years in order to free a place of some of the rusts.

The Potato Blights.—Other fungous diseases somewhat like the rusts are the potato blights. These cost the people of the United States millions of dollars each year. There are two potato blights, the early and the late. The early blight (see botany for Alternaria solani) attacks the leaves and stems only. The late blight attacks both stems and the tubers, giving us the black potato rot. The early blight ma So weaken the plants that they fall an easy prey to the late blight. The early blight affords a place where a child may do some missionary work as he goes to and from school. The farmer is busy, very busy. If he spent his time watching his potato plants, he would get little else done. The early blight comes " like a thief in the night." Sometimes in a very few days a field is blighted beyond recovery. Suppose a teacher were to lead her pupils to be on the look-out. The blight appears as grayish-brown spots on the leaves: The brown spots soon become hard, the leaves and stems turn yellow and later brown (Fig. 107). Some farmers who do not under-stand the blight, think that their potatoes have ripened prematurely. But they have had the life eaten out of them by the hyphae of the fungus. Nothing can be done to kill the blight once it has entered a leaf, but if there is Bordeaux mixture on the leaves, when the spore lights the mixture kills the spore as it germinates. Again we may accomplish much by breeding for a blight-resistant potato (see tuber-unit planting.

The Late Blight.—Later in the season the potato tops may be attacked by the other and even more serious disease, the late blight (Phytopthora infestans), which, as stated above, injures both stems and tubers. This late blight gives us the black rot, which may cause serious trouble after the potatoes are in winter quarters. This late blight offers an interesting illustration of how de-pendent farmers are on the weather. This blight does not develop enough to do serious injury except when the temperature is between 72 ° and 74° F. If the temperature rises or falls much below 72° to 74°, it checks the growth of the disease. The blight appears as brownish or black spots that soon become soft and foul smelling. The disease spreads rapidly over the leaves and down the stems where it enters some of the tubers. The tubers affected become black, soft, nasty, ill-smelling, " rotten potatoes." So suddenly does the disease appear and so rapidly does it spread that a healthy field may in less than a week appear as though a fire had swept over it. In 1845 the disease caused the terrible famine in Ireland and in parts of Europe and the United States.

At times like that, when a teacher has saved to some poor family its food supply, she feels that life is worth living and teaching worth while. Children should be taught to be alert for the signs of the coming of the blight. The farmer should have spray machinery in order and materials on hand with which to make the Bordeaux mixture.

Potato Scab.—This is an-- other fungous disease which is very destructive. We know its signs by the eaten surfaces of the tubers. The disease lives on the tubers and is planted with them. It lives over winter in the soil and may do injury if the field is planted to potatoes more than one year at a time or if the ad-joining field is planted to potatoes and machinery drags soil particles from one part to another or one field to the other. Before cutting the tubers for planting they may be soaked for an hour to an hour and a half in a 1 to 32 solution of formaldehyde. This is made by adding 1 pound of formaldehyde to 32 gallons of water. The formaline may be poured into a barrel, the potatoes put into a gunny sack and immersed in the liquid, then removed, allowed to dry and cut for seed.

The Grain Smuts.—Grain smuts (Fig. 108) are another kind of disease easily controlled on some of the grains. Seed oats may be sprayed, or when one has only a small amount of seed it may be treated by a twenty minutes' immersion in a 1 pound to 40 solution of formaldehyde. If sprayed, about 8 inches of oats should be shovelled into a wagon box, levelled and then thoroughly sprinkled with a 1 to 30 or 40 solution of formalde hyde and water. Another 8 inches may be shovelled on to the first 8 inches and sprayed and another 8 inches and sprayed. Then all should be covered with horse blankets, sacks or old pieces of carpet and left to fumigate for ten or twelve hours. Then the oats should be shovelled out on to a floor where they may be stirred frequently and thoroughly dried. The oats may be sown directly from the fumigation, if due allowance can be made for their being swollen and if one has a force seeder that will sow damp grain. It is claimed that from $30,000,000 to $40,000,000 are saved to the people of the United States each year from the discovery of this treatment alone. Evidently if " Agriculture is the hope of the nation, the hope of agriculture is applied science."

About harvest time, if the school be in session, the teacher may impress upon the pupils the necessity for this work by having them go to the field and mark off two square feet, or throw a barrel hoop over into the field and then count the number of grain stalks in the square or hoop, and then find the fraction or percentage that is destroyed by smut. Figure the loss per acre. The seed for 10 acres can be treated in four hours or less. What is the income per hour for treating seed ? The seed oats need not be injured in any way if the formaline fumigating is properly done.

Bacteria.—Other plant and animal diseases are due to bacteria. These are the smallest known plants. Most botanists prefer to classify the bacteria as a separate kind of plants from the fungi. The President of the American Medical Association suggests that we classify the bacteria as below both plants and animals. Medical doctors are very generally coming to the conclusion that most animal diseases are due to bacteria. Bacteria are so numerous and so varied that the study of them has given us a new science called Bacteriology. -These organisms are microscopic and multiply by division of the parent cell, some of them multiplying as frequently as once every twenty minutes, at which rate a single parent would give rise to over 280,000,-000,000 in a day. Many of these bacteria are beneficial in the extreme. Probably no decay can take place without bacteria. Think of what this would mean if every dead plant and animal of the past were lying on the surface of the earth today. We could not pass around, over and among them. Our soil could ot get nitrates from the humus to feed new plants. We would have no plants to gather nitrogen from the air (Fig. 77). The bacteria also cause many familiar phenomena of the farm. They cause the disagreeable odors which warn us of danger. The bacteria in milk cause it to turn sour, bitter, or to take on the desirable flavors of butter and cheese.

While there are many beneficial bacteria, there are also many destructive bacteria which sometimes begin the disintegration of the tissues of living plants and animals. Diphtheria, fevers, and some blights are among these destructive bacteria. It is now believed that the injury to plants and animals comes partly from the weakening of the tissues, but mostly from poisons called toxines which the bacteria give off.

The Fire Blight.--One of the most destructive of the plant diseases is fire blight, which attacks apple and pear trees. The bacteria live in the cambium layer just under the bark. They kill the stem and thus cause the bark to become rough, withered and dark; the leaves turn yellow and then brown. The pith turns mealy and bright yellow. We say " the tree is dying at the top." The disease may be eradicated by cutting off the diseased limbs about a foot below the affected bark and then burning the limbs, leaves and all. If neglected, the disease will spread down the tree and then to other trees, and thus in a very few years destroy a whole orchard. If one cuts off more than one limb, the knife blade should be wiped or dipped in kerosene or carbolic acid to prevent its introducing the disease into fresh wood. Let the teacher send the children home to search for fire blight. From the discussion at the school much valuable information may be disseminated throughout the neighborhood.

The Black-knot.—Black-knot is a disease of plum and cherry trees (Fig. 109). Its presence is indicated by the peculiar knarled knots on the limbs. Like fire blight of apple and pear trees, the black-knot must be cut out and burned or it will injure all the trees of the orchard and neighborhood. Nursery stock should be inspected very carefully for these diseases and rejected upon detection of the slightest symptoms. Teachers should help to mould a healthy public opinion, to cooperate with their Experiment Stations and Agricultural Departments for the efficient enforcement of laws against the spread of such diseases.

The Club Root.— A disease attacking truck crops is the club root of cabbage, turnips, cauliflower, etc. Heavy liming of the soil, and wide rotation of crops so that these crops do not come on infested soil for some years, are the remedies.

Peach Curl.—Peach curl can be controlled by spraying with Bordeaux mixture. It is estimated that this single disease damages $3,000,000 worth of fruit each season.

Cotton and tobacco wilts destroy the plants completely and stay in the soil for years. The breeding and planting of resistant varieties seem to be the remedies.

Brown Rot.—Fruit mould, or brown rot, is a serious disease of many of the different kinds of fruit. It attacks the fruit on the tree. The fruit shrinks, dries up, grows black and drops or clings persistently to the tree. The disease may be controlled by gathering and burning diseased fruit as soon as it appears and the next season spraying with Bordeaux mixture or as directed by the Experiment Station spray calendars.

Peach Yellows.—Peach yellows is probably a bacterial disease ; but as near as I can learn the " peach yellows " germs, like the smallpox germs, if there be such, have not been separated, identified, or grown in pure cultures. The peach yellows must be controlled by growing resistant varieties, not planting the seeds of affected fruit, and the eradication by burning of affected trees. Chestnut Tree Blight.—This terrible scourge, introduced probably from Japan, has already done some $30,000,000 of damage. The teacher should get copies of the special reports of her State Commission or Experiment Station, and if in a State where chestnuts are grown have a special lesson, or part of her Arbor Day program on the chestnut tree blight. Breeding resistant trees and eradication of infested trees seem now to be the only remedies.

Spraying.—The principles underlying the farm operation called spraying should be thoroughly understood (Figs. 110-114). We wish to keep the mind of the farm boy open and yet we hope to give him knowledge enough to protect him from many kinds of fraud imposed on the people by the patent medicine quacks. If the pith or cambium layer of a plant is the seat of the disease, it is hard to see how anything can be done more than to cut the plant off well down to unaffected tissue, cut it off with sterilized knife or saw and burn the affected part. If the disease attacks the surface, if one wishes to prevent the en-trance of the spores, or if one wishes to check the spread of a disease which lives on the surface, there is a use for spraying. The Bordeaux mixture or the lime-sulfur mixture, formulae for which are given in Chapter XV, is used. The lime-sulfur is probably the more effective, but there is less danger of injuring the foliage by using the Bordeaux mixture. But farm folk must be taught to keep a constant watch for the appearance of the diseases and then remove the diseased parts as soon as possible, or if it be a disease easily held in check by spraying, spray at once upon noticing the appearance of the disease. " Eternal vigilance is the price of peace."

Animal Diseases: Tuberculosis.- Bacteria cause a number of very destructive animal diseases among which is the great "white plague" that is now killing more people in the United States than any other known destructive agency. Specialists are not yet agreed as to whether cattle tuberculosis is the same thing as that which affects people, or as to whether one is the cause of, or can be contracted from the other. The evidence seems to be very much in favor of the view that bovine tuberculosis may be the cause of human tuberculosis or consumption. The bacteria of this disease may attack any organ of the body. Thus a cow may have tuberculosis of the jaw, brain, kidneys, muscles, intestines, udder, or other parts. It is claimed by the Bureau of Animal Indus-try that it is impossible to detect the germs in the milk of affected cows where there is absolute cleanliness in the milking and where there is no tuberculosis of the udder or milk glands. But it is practically impossible to be clean when milking. It should, however, be made clear to the boys and girls that danger is reduced just in proportion as the place where the cow stands, the udder of the cow at milking time, the pail and other utensils, the hands and clothing of the milker and the air of the places where the milking is done and the milk is stored, are kept clean.

The symptoms of tuberculosis are not easily detected until the case is well developed. In both farm animals and human beings, a gradual loss of flesh without any apparent cause is apt to be the first symptom. This means, in case of the farm animals, that the farmer wastes his feed on animals that grow lighter all the time while often increasing the amount of feed consumed. In case of the cow, an irregular milk flow is suspicious, a tendency for the hair to stand on end and look dry, a cough when the animal rises or starts quickly, especially on cold days, a humped position when standing and a general lack of life and vitality are all indications that the disease may be present. But the tuberculin treatment is the most reliable test. Post-mortem examinations reveal the fact that practically every animal that reacts to the test has tuberculosis. There is no known remedy for farm animals; they are kept at a loss and hence should be gotten rid of as soon as possible. In the case of human beings there are many who recover. Where the disease is feared, a specialist should be consulted at once.

Tuberculosis a House Disease.—Tuberculosis is a house or barn disease. Think of it, out on the wide, wide prairies, the most prevalent diseases are caused by the lack of fresh air. The rule says, " A cubic foot of air for each pound of animal, with rather more than less for human beings and horses." A cubic foot to a pound applies only where there is good ventilation, that is, where the air comes into the stable or house through many small openings instead of through large openings which allow draughts and which give too much air to the animals next to the sides and too little to those nearer the centre of the building. Dairy cows are generally thin and hence must be protected from the biting blasts of cold winter days.

School-houses may become veritable breeding places for all the worst contagious diseases. If a school building is well ventilated, that is, so that the air is all changed as often as once each half-hour, each child requires, if the ceiling be ten feet high, a space at least three by four feet. Many of our country schools are too small and our teachers should help to mould public opinion in favor of better and larger buildings. It is practically impossible to change the air of a school building every half-hour and keep the room at a comfortable temperature, and therefore the only safe way is to mark the building off into strips six feet wide and then give each child a seating space of at least three feet. Small diverting boards placed under the window sash permit the air to come into the room in an upward current. This is a splendid method of ventilating a school-house unless the air fall heavily on the heads of some of the pupils near the opposite side of the room. Cheese cloth, about fifteen inches wide and as long as the window is wide, may be tacked to the window sash, prefer-ably the upper, and then to the casing so that the sash may be raised and lowered freely. When the sash is lowered, it stretches the cloth which covers the opening in the window. This cloth allows air to pass in or out quite readily but prevents draughts on the children's heads.

Other Animal Diseases.—There are many animal diseases the presence of any one of which in a district may make it advisable to give a series of lessons and have one or two booklets made on that disease, giving the symptoms, treatment, etc. There is a very close resemblance between the diseases of animals and the diseases of human beings. For example, practically all of the young stock which I have lost in recent years have died from pneumonia. This dread disease comes to colts, cattle, hogs, children, or to men and women most readily after the body is weakened from some other ailment. Hogs die not so much from cholera alone (Fig. 115) but the cholera weakens them so that the pneumonia kills them. It is the belief of most well-informed people that we carry the germs of disease with us much of the time, but if the body is clean, well rested, has proper food and plenty of fresh air, the scavengers of the body easily hold the disease germs in check. But if we over-eat, or if we eat improper food, the disease germs get the start of the scavengers. Now green corn and hog cholera may be explained on the ground that, with a hog at normal temperature, the cholera germs are not apt to get the start, but if the hog is fed on green corn and the temperature of its body is kept a few degrees above normal for several days, the germs become so numerous that the protective agencies of the normal animal cannot cope with them.

Science seems to have given us an almost sure preventative for some diseases. Among these are typhoid fever, smallpox, and hog cholera. For cholera the serum-virus treatment is used successfully, and, where carefully administered before the hogs are seriously infected, seems to be a very reliable means of immunizing hogs. In most cases it is best to use the treatment when cholera is known to be in the neighborhood. In cases where the serum is administered after the hogs of a farmer are known to be diseased, only about 60 per cent seem to be saved, while, if administered before a herd is infected, as high as 100 per cent have been saved (Fig. 115).

Information in the Goverment Bulletins.—The National Department of Agriculture and the State Experiment Stations send out splendid literature on nearly all the diseases of the different farm animals. The library of the redirected school should be the place where the farmers can go to learn the very best and the very latest that is to be had on the diseases of both their plants and their animals. The boys and girls of the new school must learn that modern sanitation is a study of great interest and of practical value; that civics and health are more closely related than we have thought possible in the past. The new farmer should learn that physics, chemistry, botany, zoology and some bacteriology are necessary to enable one to intelligently care for farm animals. While these studies may need redirecting, yet they are the foundation studies for a clear understanding of plant and animal diseases. He who starts life as a farmer without them starts greatly handicapped.

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