Sources Of Injury To Alfalfa





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.





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