Legumes in the South

J. L. Weimer, J. Lewis Allison.

The annual legumes grown in the Southeastern States are classified into two groups, winter and summer annuals, according to their adaptation. They are grown in rotations, for green manure, intermixed with a main crop but subsidiary to it, following a main crop, and for hay and pasture. Some are grown as seed crops. A few perennial legumes are also grown for soil improvement, erosion control, hay, and pasture.

The winter annuals are field pea (Pisum arvense), vetch (Vicia species), crimson clover (Trifolium incornatum), lupine (Lupinus species), roughpea (Lot1grus hirsutus), and bur-clover (Medicago species).

The summer annuals are lespedeza (Lespedezo species), cowpea (Vigna sinensis), velvetbean (Stizolobium species), crotalaria (Crotalaria species), and alyceclover (Alysicarpus vaginalis).

The perennials are kudzu (Pueraria thunbergiana), sericea lespedeza (Lespedeza cuneata), and big trefoil (Lotus uliginosus).

None of them is native to the Southeast. All are susceptible to diseases, some of which are widespread and serious. The diseases are caused by bacteria, fungi, viruses, nematodes, and parasitic seed plants.

Root knot nematodes (Meloidogyne species) occur throughout the Southeastern States. They are usually more abundant in sandy soils than in heavy soils and cause greater damage to the roots of susceptible plants during the summer than in the winter, although they are active and do multiply to some extent on the roots of winter crops. All the legumes we named, except species of Crotalaria, are susceptible to root knot nematodes; their culture in areas where nematodes are present tends to increase the nematode population in the soil and to increase the possible damage to susceptible crops that follow in rotations.

THE FIELD PEA (represented by the Austrian winter) is grown largely as a soil-improvement crop. It has lost favor with some growers because of competition from the blue lupine, its failure to produce seed well in the Southeast, and its susceptibility to diseases.

The most destructive of the diseases in most years is caused by the fungi Ascochyta pinodella and Mycosphaerella pinodes, which involve so much of the stem tissue and turn it dark brown or black that the name black stem is applied to the disease they produce. All above-ground parts of the plant are susceptible to it. Sometimes the plants are killed before they can produce seed. The disease may live over summer in the seed or soil. The best way to control it therefore is to plant disease-free seed and practice a rotation of 3 or 4 years.

Another common disease of pea is leaf blotch, caused by the fungus Septoria pisi. It usually is the first to appear on the seedlings in the autumn. Often it is present a month or so after planting time. It attacks the first leaves, causing the tissues to turn yellow and later brown. Gradually it kills them. Brown or black pycnidia soon appear in the diseased areas. In them are formed the spores, which spread the disease still further. A single blotch may involve the petioles and tendrils and run down these into the stem and girdle it. It usually does not involve as much of the stem above or below the node as does the black stem. The blotch disease continues to spread in winter, when it often is too cold for the black stem. Rotation is the only control method we know of.

peas are commonly attacked in spring by powdery mildew, caused by the fungus Erysiphe polygoni. The mildew attacks the lower leaves first and gradually spreads toward the top. The mildew fungus gives the plant a whitish color as if it had been dusted with flour. Seriously affected plants eventually die. Because the disease does not appear until late spring, it usually is not very injurious if the crop is plowed under for green manure. This disease and the others we mentioned largely are responsible for the low yield of seed. No control method is known.

Root rot, caused by the fungus Aphanomyces euteiches, is a destructive disease of peas. In late winter or spring it gives a dwarfed appearance and pale yellow color to the affected plants. The affected roots and underground part of the stem are slightly darker in color than the healthy parts and have a moist rot, mostly on the outer layers. The discolored and dwarfed condition of the tops is brought about by the inefficient functioning of the diseased roots. Many of the plants die but others, although alive, make little growth and set little seed. The Romack variety of pea is resistant to the disease.

Winter peas are susceptible to root knot nematodes but usually are not seriously damaged by them, except in the southernmost part of the pea belt and in some of the soils of the Coastal Plain.

VETCHES are planted largely for soil improvement and winter pasture, but they have lost favor in areas in which lupines can be grown. Diseases also have been a factor.

One of the most common fungus diseases is anthracnose, caused by Colletotrichum villosum. On the leaves it produces small, round spots, which first are light green and later become light brown or gray, with a brown or red border. The stem lesions are linear and usually dark brown. On the pods the lesions are dark red, with a darker margin and lighter center. Severe defoliation and death of the entire plant may occur during wet weather. The disease can be controlled by rotation or by planting such resistant species as the bigflower vetch (Vicia grandiflora), monantha vetch (V. articulate), and Hungarian vetch (V. pannonica).

Some species are quite susceptible to a blight caused by the Ascochyta fungi that attack pea. The blight causes more or less circular spots on the leaves and long, reddish lesions, which later turn gray on the stems. The lesions usually have a reddish border surrounding the grayish center. Black pycnidia are scattered over the gray area. Pod lesions are like those on the stem. Leaves, stems, and pods may be killed. The disease can be controlled by rotation of crops.

Several species of vetch are rather severely attacked by a leaf spot caused by the fungus Botrviis cinerea. Small, dark-red spots are produced on the leaflets, stems, tendrils, and petioles of some species. The spots may be so numerous that they cause considerable defoliation and kill the stems. The disease is especially serious in wet weather. It can be controlled by rotation and by planting resistant species, such as hairy vetch (Vicia villosa) and purple vetch (V. atropurpurea).

Many vetches are quite susceptible to the aphanomyces root rot. Hairy vetch is resistant and should be used when that fungus is known to occur in the soil. Vetches are susceptible to root knot nematodes but usually are not seriously injured by them.

CRIMSON CLOVER is grown for soil improvement and pasture throughout the Southeastern States and in some places as a seed crop. The development of hard-seeded varieties, such as Dixie and Auburn, which are maintained by volunteer reseeding for several years, has increased its use for pasture.

Crimson clover is prey to several diseases. Crown and stem rot, caused by the fungus Sclerotinia trifoliorum, is the most destructive. It develops and spreads rapidly in cool, wet weather. It can be recognized by the scalded, circular patches of dead and dying plants in affected fields.

The fungus produces small, black, tough bodies about the size of wheat kernels after it has destroyed the plants. The sclerotial bodies carry the fungus through hot weather, which is unfavorable for its growth. They germinate in fall when the weather is again cool and wet. Small, inconspicuous structures like toadstools, which develop from them, produce the spores or seeds of the fungus. These reinfect plants and start the disease off anew each year.

Rotations that use crops not susceptible to the disease are one way of holding it in check. The fungus dies in the soil when susceptible plants are absent. Deep plowing of land is another way of controlling it. The sclerotial bodies are buried deeply and cannot get their sporebearing structures to the soil surface. The normal life cycle of the fungus is broken and it soon dies.

Sooty blotch, caused by the fungus Cymadothea trifolii, appears as black, crusty blotches on the under sides of leaves and on petioles. It prefers wet, cool weather and causes the greatest damage in late fall while plants are still in the seedling stage. No control method is known.

Crimson clover is susceptible to root knot nematodes. Nematode injury stunts and yellows the plants.

THE BLUE LUPINE has largely replaced peas and vetches as a soil-improvement crop in places where it is adapted because it grows vigorously and yields abundant seed. The sweet strains of lupine also provide winter forage. Like the other winter legumes, however, the lupines are subject to a number of diseases.

Anthracnose, caused by the fungus Glomerella cingulata, is destructive in some areas. It attacks all above ground parts of the plant. The first symptoms are dark-colored, circular spots on the cotyledons. From those lesions the disease usually spreads to the stem, where it causes black bands, which may eventually girdle the stem and kill the plant. Small, dark lesions, usually one-third to one-half as wide as the leaflet and having light centers and dark borders, may be found on the leaflets. Older stems and branches may have many long, brown lesions, often with concentric rings on the surface. Pod lesions are nearly black and circular or irregular; they may involve half or more of the pod, often killing it and destroying the seeds within. Anthracnose can be controlled by planting disease-free seed on land that has not grown lupines for at least 2 or 3 years. As the fungus in the seed dies in about 18 months, seed held over until the second planting time after harvest is free of disease.

Brown spot, caused by the fungus Ceratophorum setosum, appears as small, nearly black spots on leaves, petioles, stems, blossoms, and pods. When the spots are very abundant, severe defoliation results. The spots may be so abundant on the stems that they merge and form large, black cankers, which may girdle and kill the stem. The causal fungus may grow through the pod and enter the seed. The fungus in the seed remains alive for more than 2 years; hence, 2-year-old seed is not disease-free, as is that affected with the anthracnose fungus. Rotation is the only control method known.

All above-ground parts of the lupine plant are susceptible to powdery mildew. The disease appears too late in the spring, except possibly in the extreme southern part of the lupine belt, to do much harm to the part of the crop turned under for green manure, but it can cause defoliation and loss of the seed crop. No control method is known.