« AnteriorContinuar »
field, liming the seed, and soaking the seed over night in common salt lye. Though the efficacy of the remedies was doubted, there must have been some beneficial results, for it is claimed that the seed was invariably steeped. By the middle of the nineteenth century there were many methods of steeping, liming and brining wheat to prevent smut. It was found that the use of a solution of arsenic gave a clean crop from smutty seed.
Just how fully the nature of smut was understood by these early writers does not seem to be clear, but they must have had considerable knowledge of the disease in order to pursue such correct principles in endeavoring to effect a cure. The black dust frequently filling the kernels of ripening wheat consists of thousands of germs of the parasitic smut fungus. These germs, or spores, have a great capacity for spreading over the fields, but the only real danger seems to be from those spores which lodge on healthy kernels, generally in the hairy ends. Chances are slight of clean seed being infected by being sown on ground containing smut spores. Spores have the same function as seeds of higher plants, and, the infected kernels of wheat being sown, the spores germinate at the same time as the wheat. The slender filaments penetrate the tissues of the wheat plant before the first leaf is put forth. From this point its growth is within the wheat plant, both plants growing together. It seems to be still undecided how these threads proceed below the upper two joints of the mature wheat plant, whether they pass upward through the pithy region of the stalks, or whether they follow the surface tissues, but it is probable that the method of smut growth is uniform throughout the entire plant. The fungus seems to die as it passes upward, and leaves few traces of its path.
In the mature wheat plant smut seems to be found only in the chlorophyl bearing parenchymatic tissues. Nearly 30 rows of breathing pores in the skin covering of the straw run lengthwise with the stalk. Under these rows of pores are layers of succulent cells which produce the food eventually used in forming the wheat grains. The smut filaments remain close to the open pores, absorbing and taking the place of this cellular structure with its chlorophyl and protoplasm. No other cellular tissues are disturbed, and until the heads develop the presence of the smut can scarcely be detected without the aid of a microscope. A mass of smut threads then absorbs all the nourishment, fills the flower or grain, and soon converts it into a mass of spores. As the parasite lives at the expense of its host, the latter is weakened and stunted in proportion to the amount of smut. This may be great enough to dwarf the plants so as to prevent the formation of heads, or even to cause the stalks to die back to the ground, or it may be so little that the heads are never reached, simply the straw being infected. Much of the straw may be thus infected, greatly reducing the yield, even though apparently uninjured heads are formed. Smut filaments have also been found in grains which had formed starch.1 In general, smut and wheat seem to de
SECTIONS OF SMUTTED WHEAT STRAW
At the left is a longitudinal section of a wheat straw and at the right a cross section, a, epidermal cells; b, smut filaments; c, fibrous cells; d, internal tissues.
mand about the same meteorological conditions for their best growth. Smut will successfully pass the winter, even upon the open ground in North Dakota. Germs two years old have not lost their power of producing smut in a crop.2
Grains of wheat affected by stinking smut are slightly larger and more irregular than healthy ones. Such kernels, the socalled "smut-balls," are easily broken open, and the darkbrown powder with which they are filled has a very disagreeable and penetrating odor that pervades the whole bin of wheat, even if only a small per cent of the kernels are smutted. On this account they differ from all other grain smuts in that their presence can be easily recognized. Sometimes 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.
1 Bolley, Proc. Tri-State Grain Growers' Ass'n., 1900. p. 86.
2 Rept N. D. Agr. Exp Sta., 1901, p. 34.
Loose Smut of Wheat differs from the stinking smut in these respects: At germination its spores develop a chain of cells instead of an undivided tube; it has no fetid odor; it attacks both kernel and chaff; and it ripens when the healthy wheat is in flour. By harvest time the spores have all taken wings upon the wind, leaving a naked stalk in place of the head. It is known to occur in Europe, North America, northern Africa, central Asia and the West Indies. There are many localities in the United States 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 sown without drying, the drill must be set accordingly. STINKING SMUT
Corrosive Sublimate (Mercuric Chloride, Eg Cf.)—This may be used at the rate of 1 lb. to 50 gallons of water (2y2 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 (Cm SO').—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.1
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 Freeman, Minn. Plant Diseases (1905), p. 297.