Dodder has been a troublesome weed in lespedeza. If the crop of lespedeza is used for pasturage or hay, the presence of dodder is not serious. In a seed crop, dodder not only reduces yields but also makes the seed unmarketable or salable only at a reduced price. Dodder can be eradicated from a field by burning it, spraying it, or cutting and removing it. Fields that are pastured heavily or are cut for hay have relatively little dodder.
Other weeds in lespedeza are objectionable because they reduce the quality of hay and pasturage, and it is often difficult to separate weed seed from the lespedeza seed. Many weeds are eliminated by planting lespedeza after a cleancultivated crop or by seeding lespedeza with small grain.
Broadleaved weeds are frequently a problem in stands of lespedeza. Spraying with 2,4-D when the lespedeza is approximately 4 inches tall has given good control. One-half to 1 pound per acre of the amine forms of-2,4-D or 1/4 to 1/2 pound per acre of the ester forms has been satisfactory.
The bacterial wilt disease is generally distributed wherever lespedeza is grown. It has been studied most extensively in Missouri, where reductions of 30 to 50 percent in forage yield have been recorded.
Bacterial wilt occurs principally in strains of annual lespedeza. The causal bacteria are carried in or on the seeds. They can also persist from one season to the next in diseased stems and leaves. The bacteria are disseminated by wind and rain and possibly by grazing and mowing. They gain entrance to plants through wounds in the stems and leaves
Early infection occurs as dark, water-soaked spots on the leaves. The infected leaves soon become grayish brown, dry, and curled. The bacteria then spread to the water-conducting tissues, which they fill, and the plants wilt and die. Sometimes only individual stems are affected and killed. Since the bacteria are seed borne, only disease-free seed should be planted. -Some strains are more tolerant to the disease than others; however, only Summit lespedeza is resistant to bacterial wilt. It should be used in areas where this disease is serious.
This disease is caused by a fungus, and it occurs wherever lespedeza is grown. It usually develops late in the season, but it may cause some premature defoliation.
The mildew fungus overwinters on old leaves and stems. Spores are blown to new leaves, where they start infection. When abundant infection occurs, the leaves turn whitish. If the infection is light, diseased leaves develop whitish patches on the upper surface; they look as if they had been dusted with lime or flour.
The disease can be controlled by planting Rowan, which has some resistance.
3 Prepared by K. W. Kreitlow, research pathologist, Crops Research Division.
