. Diseases of field crops. Plant diseases. Diseases of Field Crops 13 dwarfed and the leaves somewhat mottled. It is seen mostly in the first crop, and is not serious. Root-Knot Nematode.—Although alfalfa is not seriously damaged, farmers should understand that it is by no means immune to this omniv- orous pest (Heterodera marioni), and should not be planted in a rota- tion designed to starve out nematodes. (See general discussion p. 68.) Rust.—Alfalfa is attacked by a true rust, Uromyces striatus, which causes powdery, dark-brown dots on the leaves, mostly on the undersides (fig. 7). The dise
. Diseases of field crops. Plant diseases. Diseases of Field Crops 13 dwarfed and the leaves somewhat mottled. It is seen mostly in the first crop, and is not serious. Root-Knot Nematode.—Although alfalfa is not seriously damaged, farmers should understand that it is by no means immune to this omniv- orous pest (Heterodera marioni), and should not be planted in a rota- tion designed to starve out nematodes. (See general discussion p. 68.) Rust.—Alfalfa is attacked by a true rust, Uromyces striatus, which causes powdery, dark-brown dots on the leaves, mostly on the undersides (fig. 7). The diseased leaves drop off and, if rust is abundant, the hay. Fig. 7.—The appearance of rust: A, lower surface of leaves ; B, upper surface. Rust pustules are usually most conspicuous on the undersides of the leaves. (From Cir. 326.) crop is much reduced both in quality and quantity. The same treatment is recommended as for leaf spot. Stem Nematode.—This nematode, or eelworm, Ditylenchus dipsaci (see p. 68), lives in the stems of the alfalfa aboveground, with the effect that some of the stalks and branches are short, swollen, and deformed (fig. 8). The yield is reduced and the life of the stand shortened. This parasite is a strain of the bulb nematode, which attacks narcissus and other flowering bulbs. Other strains of the same species attack garlic, strawberries, cereals, certain weeds, and other plants. The strain from one host does not usually pass to another : the alfalfa stem nematode, for instance, does not attack bulbs or strawberries, although the worms in the different hosts seem to be of the same Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Smith, Ralph E. (Ralph Eliot), 1874-1953. Berkeley, Calif. : College of Agriculture, University of California
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