Peculiar Nodules in Groups on Small Rootlets
and distant from the large alfalfa roots. From Michigan Experiment Station Bulletin No. 225
Alfalfa Roots Showing Normal Nodules
small and near the large roots. From Michigan Experiment Station Bulletin No. 225
From an excellent article on the dodder that infests alfalfa (Cuscuta epithymum) by Mr. F. E. Dawley, a New York authority on alfalfa, and printed with illustrations in the Country Gentleman, the excerpts here following are taken:
“The only sure method of keeping alfalfa fields free from dodder is through exercising greater caution in the purchase of seed. There is no reason why thoroughly recleaned alfalfa seed should have any dodder seed in it, as reference to the [illustrations] will show. The relative sizes and forms of the seeds of alfalfa and dodder are shown herewith. It will be seen that there is a marked difference in both the sizes and the shapes of the seeds. The alfalfa seed is shaped like a little kidney bean, and varies in color from light yellowish-green to a rich golden-yellow, and in some instances, because of weathering, or sweating in the cock, or perhaps standing too long, it shows a reddish-brown color. The dodder seed is darker in color than the alfalfa, all of that which I have succeeded in gathering from the plants being a rich golden-brown. The accompanying [illustrations] show the form of the dodder and alfalfa seed respectively.
“The seeds, being sown, germinate in the soil, throwing up a slender, thread-like stem somewhat resembling a corn silk, which retains its connection with the ground until it comes in contact with the stem of the alfalfa plant. It twines around this tightly, sending its feeding suckers through the outside bark, and as soon as it is firmly attached to the host plant, the ground connection is severed and it is sustained by the plant juices which are taken in by the suckers. It continues to grow and spread, twining around other stalks and increasing very rapidly until a colony is established. Continuing to grow, it climbs toward the upper portion of the plants, feeding on their juices and sapping their vitality, but never goes to the extreme top, seeming to prefer the dampness and darkness of the matted alfalfa rather than sunlight. The plants first attacked begin to die, and the dodder, spreading out in all directions, forms a circle or ring.
“The rapidity with which the pest spreads makes it a serious menace to the alfalfa grower. Comparatively little work has been done by scientific men in studying the dodders and methods of eradication, and the fact that the little rootlets or suckers (haustoria) become so firmly affixed to the host plant that it must be destroyed together with the parasite, has made the work hard and the results obtained unsatisfactory. There are a number of methods by which dodder may be spread through a field. As soon as it becomes thoroughly established on a host plant, the many little branches, waving about like the shoot produced from the seed, attach themselves to other plants, and thus the colony is increased in size. In legumes, the host plant first attacked soon dies, but before this occurs, the parasite has become firmly established on adjoining plants and is reaching out and completing the colony. As soon as a host dies, the dodder also perishes, but before this happens it is very likely to have blossomed and seeded.
“In the operations of mowing, tedding, raking and drawing the alfalfa hay, these little colonies are spread about the fields by the machines and the workmen, and on the horses’ feet. The sale of infested hay is a prolific means of dissemination. Hunters and pleasure seekers, walking through the fields, notice the peculiar corn-silk-like growths and often, by picking up particles of it which are soon cast away, establish new colonies. The flower is very peculiar and attracts the attention of people passing, who are apt to pick them together with some of the maturing seed, and scatter these over the fields. In a pastured field, the animals spread the seed to some extent while moving from place to place in feeding. The most serious menace, however, is from the purchase of impure seed; farmers should always be absolutely certain that the alfalfa seed which they are buying is thoroughly recleaned and that no small weed seed is to be found in it. One should never sow clover or alfalfa from a field or even from a locality in which dodder is known to exist. It is probable that the seeds thoroughly ripened will retain their germinating powers for some years. The purchase of hay from dodder infested fields, or the purchase of manure from barns where infested hay has been fed, are sure sources of contamination.