Stewart's Disease of Corn
Fact Sheet Page 727.10 Date 1-1979
COOPERATIVE EXTENSION NEW YORK STATE CORNELL UNIVERSITY
by Arden Sherf and Thomas Woods Dept. of Plant Pathology Cornell University
|Stewart's disease of corn is common throughout the eastern United States. It is a bacterial disease, caused by the bacterium Erwinia stewartii (E. F. Sm.) Dye. Unlike many fungal diseases of corn, damp weather and heavy dews are not necessary for a disease epidemic to occur. The disease on sweet corn is referred to as Stewart's wilt because of the wilting of foliage often associated with infection. In addition to wilting, plants may be stunted, and in severe cases death may result. Wilting and stunting are caused by slimy masses of bacteria, which grow in the vascular tissue of the foliage and disrupt the normal metabolism of the leaves. Symptoms of the disease on sweet corn may appear at any stage in the development of the plant. The most diagnostic symptom of the disease is the presence on the leaves of yellow to brown stripes or streaks with wavy or irregular margins. These streaks may be quite short or may extend the entire length of the leaf. The symptoms of Stewart's wilt may sometimes be confused with those of fungus leaf blights or with frost injury. On field corn the disease is referred to as Stewart's leaf blight. Symptoms usually do not appear until after tasseling. At this time the characteristic streaks may be seen on the leaves of infected plants. Several lesions may coalesce, and large areas of leaf tissue die with a resultant loss in yield of ears. Wilting and stunting of field corn are rarely associated with Stewart's leaf blight. Premature death of large areas of leaf tissue also renders the plants more susceptible to stalk rots.|
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The bacteria overwinter in the bodies of adult corn flea beetles, small, shiny black beetles, which jump much like fleas when disturbed while feeding. These beetles overwinter in the soil and, upon emergence in the spring, commence feeding on and contaminating corn seedlings. Up to 20 percent of beetles emerging from hibernation may carry the disease causing organisms. Uninfested beetles soon pick up the bacteria by feeding on infected plants and then spread the bacteria to healthy plants nearby. These beetles remain able to infect healthy plants for the rest of their lives. An entire field of corn may become infected in a relatively short period of time. Some or all plants die, and severe yield reductions result.
Although a few other species of insects have been shown to be able to transmit E. stewartii from plant to plant, none is as important in spreading the bacteria as the corn flea beetle. A series of very cold winters may reduce the population of overwintering flea beetles and thus lead to a decrease in incidence of Stewart's wilt the current crop year.
The bacteria may survive in infected seed for several months. Infected seed may be important in introducing the bacteria into an area previously free of the disease; however, only about 2 percent of the plants developing from a planting of infected kernels develop symptoms of Stewart's wilt. The infected plants may be fed upon by corn flea beetles, which pick up the bacteria and spread them from plant to plant.
Two major control measures are useful in reducing losses to Stewart's disease. The first consists of planting tolerant varieties, which will grow and produce well in spite of the presence of the pathogen. In general, later maturing varieties are more tolerant of the disease than earlier maturing ones, although several early maturing varieties are available with good tolerance to Stewart's wilt. Current sweet corn varieties with tolerance include: Bellringer, Calumet, Capitan, Comet, Defender, Gold Crest, Gold Cup, Gusto, Merit, Midway, NK 199, Pacer, Seneca Chief, Silver Queen, Sprite, Sweet Sue, Titan, Valley Market, Vanguard, Wintergreen, and Yukon. The second major control measure is the application of early insecticide sprays for controlling the overwintering flea beetle population. In areas where Stewart's wilt is known to be a potentially severe disease, insecticides should be applied when the corn first breaks ground and should be continued for several applications thereafter until the stand is well established. Consult your county Extension agent for a list of registered insecticides and rates of application.
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