Chief among the sources of injury to
alfalfa, after the plants have become established, are frost in
saturated ground, ice, floods, grasshoppers, gophers, dodder, and
pasturing by live stock in the late autumn or winter. When it happens
that two or three of these
act in conjunction, the injury following is just so much more rapid and complete. As has been intimated, where water is excessive, in a climate which in winter or spring is characterized by alternations of freezing and thawing, the plants will either have the roots snapped asunder, or they will be gradually raised out of the ground. This will only happen in soil with a subsoil more retentive than is compatible with well-doing of the highest order in the plants. The danger from this source is greatest during the first winter after sowing the plants, as then the roots are not really established. The only remedy for such a contingency is the draining of the land. Some reference has also been made to injury done through ice, where it collects in low places in land. The destructiveness of the ice depends on its thickness and its nearness to the ground. When it rests upon the ground for any considerable time the plants die. If, however, water intervenes, the plants may live when the submergence is for a limited time. One instance is on record in Onondaga County in New York State, in which alfalfa survived submergence for a considerable period under a thin sheet of water covered by three inches of ice, but when growth came it was for a time less vigorous than normal. Floods in warm weather are greatly injurious to alfalfa. The extent of the injury done increases with increase of depth in the waters of submergence, increase in stagnation in the waters, and increase in the duration of the period of overflow. Stagnant water sooner loses its dissolved nitrogen; hence, the plants cannot breathe normally. The harm done, therefore, by floods in each case can only be known by waiting to see the results. These summer floods always harm the crops temporarily, and in many instances kill them outright. Occasional periods of overflow should not prevent the sowing of alfalfa on such lands, since on these it is usually not difficult to start a new crop, but the seed should not be sown on such lands when overflow occurs at such a season. When it occurs in cool weather and quickly subsides, it may be possible to grow paying crops of alfalfa. In some areas grasshoppers are a real scourge in alfalfa fields. Because of the shade provided by the ground and the influence which this exerts in softening it, they are encouraged to deposit their eggs and remain so as to prove a source of trouble the following year. It has been found that through disking of the land both ways after sharp frosts have come is greatly effective in destroying the grasshopper eggs deposited in the soil. They are thus exposed to the action of the subsequent frosts and so perish. The disking has also tended to stimulate growth in the crop the following year. The eggs will not, of course, be all destroyed by such disking, but so large a percentage will, that the crop should be practically protected from serious injury, unless when grasshoppers come from elsewhere. It would seem correct to say that gophers do more injury to alfalfa fields in certain areas of the West than comes to them from all other sources combined. They not only destroy the plants by feeding upon them, but they fill the soil with mounds, which greatly interfere with the harvesting of the crops. They are destroyed by giving them poisoned food, trapping, shooting, and suffocating through the use of bisulphide of carbon. Poison is frequently administered by soaking grain in strychnine or dropping it on pieces of potato and putting the same in or near the burrows. Bisulphide of carbon is put upon a rag or other substance, which is put into the burrow and the opening closed. Dodder is a parasitical plant introduced, probably, in seed from Europe, which feeds upon alfalfa plants, to their destruction. The seeds of alfalfa sometimes become so impregnated with the seeds of dodder that the latter will grow where the seed is sown, thus introducing it to new centers. The dodder starts in the soil and soon throws up its golden-colored thread-like stems, which reach out and fasten on the alfalfa plants that grow sufficiently near. The dodder then loses its hold upon the soil and gets its food entirely from the alfalfa plants, which it ultimately destroys. But since the seeds of the dodder remain at least for a time in the soil, and the adjacent soil becomes infected with them, the circles in which the dodder feeds continually widen. In certain parts of New York State some fields have become so seriously affected as to lead to investigations conducted through officials from the State experiment station. Pending these investigations, the exercise of great care in the purchase of seed and the immediate plowing of the infested areas are recommended. Some reference has already been made to injurious results from pasturing close in the autumn or winter, except in the most favored alfalfa regions. In addition to what has been already said, the wisdom of not grazing alfalfa the first year is here emphasized, and also the mistake of grazing at any time when the ground is frozen, at least in areas east of and, generally speaking, adjacent to the Mississippi River.
Next: Alfalfa As A Fertilizer
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