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50 to 75 per cent of the heads in a field are smutted, and the remainder of the grain is so contaminated by the fetid spores as to be of very little value as flour and worse than useless for seed. Unchecked, these smuts increase from year to year, and they occur more or less abundantly in all wheat raising countries.
Loose Smut of Wheat differs from the stinking smut in these respects: At germination its spores develop a chain of cells
fetid odor; it attacks both kernel and chaff;
many localities in the United States STINKING SMUT where it is rare or entirely absent. A
loss of 10 per cent or more of the crop is often occasioned by loose smut, and even as high as 50 per cent, but usually it is not as destructive as the stinking smuts. It seems to be more difficult to prevent, however, so that when once introduced into a field, it is more apt to remain.
Remedies.—Any means that destroy the vitality of the smut spores adhering to seed wheat but leave the latter unimpaired in its power of germinating are a safe preventive of smutted wheat. There are several ways of accomplishing this easily and perfectly with the stinking smut. In all treatments by immersion in solution, the seed should first be stirred in water in order to skim off the smut balls. Slaked lime will hasten drying, but is not essential. If the seed is LOOSE sown without drying, the drill must be set accordingly. SMUT
CORROSIVE SUBLIMATE (Mercuric Chloride, Hg CF.)-This may be used at the rate of 1 lb. to 50 gallons of water (212 parts to 1,000). The wheat is piled upon a floor or canvas, and constantly shoveled while it is being sprayed or sprinkled, until every grain is wet over its entire surface. The use of more of the solution than is necessary to do this is injurious. The seed should then be dried.
COPPER SULPHATE (Cu SOʻ).—One pound of crystallized (not powdered) commercial copper sulphate or bluestone is used to every 25 gallons of water. The grain is soaked 12 hours in this solution, being stirred occasionally. Then, to avoid injuring the power of germination, it is immersed for a few minutes in limewater made by adding ten gallons of water to one pound of good slaked lime.
FORMALIN.--One pound of formalin (the trade name for a 40 per cent solution of formaldehyde) is diluted with 50 gallons of water. The grain is treated as in using corrosive sublimate. Each bushel of grain requires about one gallon of the solution. The grain is left in a pile for 2 or 3 hours, and is then spread out to dry. This method is not successful with formalin that is not a 40 per cent solution. Formalin rapidly loses its strength unless kept tightly corked, and careless or unscrupulous dealers sell a solution that is too dilute, or under weight on account of the bottles in which it is sold being below standard size. Formaldehyde vapor has also been found effective in destroying stinking smut.
Hot WATER OR JENSEN TREATMENT.—It is claimed that this process was discovered by J. L. Jensen of Denmark, in 1887. Hot water and quicklime were used several years before this date. In this method the seed is placed loosely in a coarsely woven gunny sack or wire-covered basket, and then dipped in water having a temperature between 132 and 133° F. The volume of water must be 6 or 8 times that of the seed treated at any one time. Lifting out and draining the grain 4 or 5 times during the treatment insures its coming in contact with water at the proper temperature. The treatment requires 10 minutes. The grain should then be dried at once, or dipped in cold water and set aside until it can be dried.
A MODIFIED HOT WATER METHOD is used in treating for loose smut, for this is not destroyed by any of the cures mentioned above. The grain is first soaked four hours in cold water, and set away in wet sacks for four hours more. It is then immersed for five minutes in water at 132° F. Some of the seed is killed by the treatment, and one-half more must be sown per acre. It has been claimed, however, that no sure method of destroying loose smut is known, and that the only available relief at present is to obtain clean seed from a smut-free district.
Results and Expenses.—These remedies seem to be entirely efficacious, and if properly and universally applied, there is no reason why smut should not be practically eradicated from the wheat fields. Before the nature of smut was fully understood, one of the unexpected results of treating it was an increase in yield greater than the result of merely replacing the smutted heads with sound ones. This was explained when it was learned that smut was often present in the straw even though it did not reach the heads. Usually the increase in yield is two or three times as great as the visible smut, but may be six or more times as great. The methods of treatment are inexpensive. In the hot water method the cost is practically only the labor required. In some of the other methods the cost of chemicals is little more than would pay for the labor in the hot water treatment. Liquid formaldehyde, which is used quite extensively in the Northwest, is found very effective, and costs only from three-fourths of one cent to two cents per acre. The treatment by sprinkling and shoveling is cheaper than dipping.
Losses continue in spite of the fact that it has often been demonstrated that smuts are controllable. During the year 1902 wheat smut caused a loss of 2.5 million dollars in the state of Washington alone. In the following year smut destroyed from 10 to 50 per cent of the wheat in parts of Wisconsin. At Winnipeg 3 to 6 per cent of the wheat offered for sale during 1904-5 was rejected on account of smut, and in 1905 as high as 75 per cent of the wheat was destroyed by smut in parts of North Dakota. While seed wheat is very commonly treated for smut, these losses show that there is still need for more educational work. It is necessary to demonstrate repeatedly the efficacy of the treatments in order to secure their adoption by the conservative farming element. This element continues
1 I'reeman, Minn. Plant Diseases (1905), p. 297.
to grow smutted wheat because it has always done so, and because the extent of the loss and the ease of its prevention are so little realized. Formerly at least one-fifth of the cereal crops was annually destroyed by smut. Smutty wheat introduces a large element of speculation into the business of elevator men, for it produces a very low grade of flour. Such wheat must be washed, an expensive process which also endangers the quality of the flour. From smutted flour the baker gets a poor, darkened product that finds little market. As a result smutted wheat is justly thrown into a very low, or "rejected” grade.
Rust.—What is popularly termed wheat rust may be the result of one or more of a number of rust fungi, parasitic plants. This disease was mentioned by Virgil. It was known in Britain before 1592. Fontana (1767) is generally accredited with connecting rust of cereals with a specific fungus, which Persoon (1797) investigated more fully, and named. Three kinds of rusts are known to attack wheat.
Puccinia coronata, the crown rust, AECIDIA ON BARBERRY is comparatively unimportant. The
two distinctive rusts are Puccinia rubigo-vera, the early, orange leaf-rust, and P. graminis, the late, stem-rust. The former is popularly called “red” and the latter “black” rust. Both species, however, produce first reddish and then black spores, but in the orange leaf-rust the red spores are far more abundant than the black ones, while in the stem-rust the black spores are the more abundant.
LIFE HISTORY.—The wheat rusts belong to that type of fungi which have several stages of development represented by different types of spore formation and separated by two or more rest periods. The life history is the development of the fungus through all its stages, and it is said to be "known” when the experimenter can take one type of spore formation and from this produce artificially all of the other types in turn through the life cycle until a return is made to the type of spore formation with which he began. Usually the types
of spores characteristic of the different stages in the life cycle of such a fungus are so different in form and character and so divergent in their modes of development and subsequent habits of growth as to mislead the investigator completely and excite no idea of relationship. Several entirely different types of hosts are frequently utilized in the life cycle. It is because of their complex life history that rusts have so long been shrouded in mystery and confusion, and inadequately understood.' · The wheat rusts produce in order, from spring to spring, four different forms of spores. (1) Aecidiospores (injuring spores) are the first spores found in the year. They occur on shrubs, or herbs other than grasses. (2) Uredospores (blight spores) appear in the early summer, and are often called summer spores.
TWO FORMS OF RUST SPORES COMMONLY FOUND ON WHEAT At the left is shown the uredospores of the red rust, commonly found in early
summer. At the right, the two-celled teleutospores or winter spores of the black rust.
ores) ang or winter, ** (4) Sporicing
These are the red spores that rust the leaf of the wheat. (3) Teleutospores (completion spores) are the last ones of the season. They are also known as resting or winter spores. Their dark color gave rise to the term “black rust." (4) Sporidia are very minute and delicate spore bodies formed in the spring on the germination tubes of the winter spores. The sporidia infect the plant that is host to the acidium stage. The question of a breeding act in the rust life cycle is still an unsettled one.
When the æcidiospore lodges upon the wheat leaf or stalk in the spring, it remains in a resting condition until a light
1 The works of Bolley, Carleton and Freeman will be found most useful in a study of rusts.