DODDER
Dodder is an annoying enemy. It is a parasite, belonging to the morning-glory family, growing from its own small seed but attaching itself very soon to the alfalfa stalk. It then separates itself from its own root and thereafter lives on the juices of the alfalfa until it ripens its seeds or has killed the alfalfa. The wisest and safest thing to do is to sow only seed so thoroughly cleaned that there will be no dodder with it. If, later, it is found that any dodder seed escaped the cleaning operations and is growing, the grower should go through the field with a knife or sickle and a large basket or sack and cut out and burn every dodder vine and every plant to which dodder is attached. If so unfortunate as to have sown seed with a considerable mixture of dodder, clip the alfalfa early in May, let the clippings dry for two or three days or longer, and then burn on the field, watching carefully to have the fire touch every part. It will facilitate a complete burning to sprinkle parts not burning readily, with kerosene. If there is a poor stand of alfalfa, largely infested with dodder, safety lies in plowing it up and cultivating the field in corn or potatoes for two or three years.
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.
“Where a newly seeded alfalfa field shows evidence of quite general dodder infection, it is useless to attempt to eradicate it, and the field should be plowed up and planted with some hoed crop for a period of years. Old fields that have been thoroughly infested will probably be more economically treated in this manner than in any other. In newly sown fields, one of the most effective methods is probably hoeing over the spots where the dodder appears, going over them once in two weeks and allowing nothing to grow on them until the dodder seed is germinated. A modification of this method has been used successfully by spading in fields where the colonies of dodder were seen, raking out all the tops, roots and branches, adding a little straw or hay and burning the mass, and then keeping the spot thoroughly hoed for a season. For fields where the colonies are small and scattered, this method of hoeing and shallow cultivation is probably the most practicable, as it helps to secure the early germination of any seeds that were left in the ground, and also kills them as soon as they are germinated. If the seed has developed, one must be careful not to spade it in too deep, as it may retain its vitality for some years if left covered in the moist soil.
“Burning has been recommended by some, raking the dodder vines and what is left of the alfalfa to the center of the colonies, putting brush or straw with it, together with some fine, light wood or chips and sprinkling with kerosene, so that the alfalfa plants will be burned close to the ground. This is necessary from the fact that the little coils of dodder close to the crown of the plants will retain their vitality and grow after a very severe burning, providing the alfalfa which is above the ground is not killed also. The most difficult problem to be confronted in killing out dodder where it has become established, arises from the fact that if these little coils which wind themselves closely around the plant are not killed or removed, the dodder will spread from these and make a new growth. Many experiments have been made with chemicals, but none of them have proved wholly successful, from the fact that these little rings were not destroyed. All the rest of the plant was killed and the production of flowers and seed prevented; but as these little rings were not killed, the dodder began growing again and continued to grow throughout the season.”