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Stewart’s wilt widely reported on field corn in Michigan
Diane Brown- Rytlewski and William Kirk
Michigan State University Department of Plant Pathology
Stewart’s wilt (also known as Stewart’s disease) is a disease of corn, caused by a bacterium, (Pantoea (Erwinia) stewartii ) carried in the digestive tract of the corn flea beetle (CFB). It is transmitted to corn plants when infected CFBs feed on them.
Though Stewart’s wilt is usually considered a problem only on seed corn inbreds and sweet corn, it was widely reported on field (dent) corn in Michigan late in the season, in August and September of 2006. Late this summer, symptoms appeared on field corn leaves as long, narrow yellow streaks that later turned brown. Sometimes entire leaves in the top portion of the plant were killed. In fields where damage was more extensive, stalk rots were also reported. The stalk rots are not caused by the Stewart’s wilt bacterium, but injury from Stewart’s wilt makes the corn plants more prone to stalk rots caused by fungi. At the time of this writing, corn harvest has not yet taken place, and the effect on yield has not been determined. It appears that in most cases, the disease affected primarily foliage.
Stewart’s wilt is common in the United States, but it only periodically reaches levels high enough to cause serious economic loss in field corn. It has not been a recent problem in Michigan. Whether or not it will be a problem in Michigan on field corn in 2007 is unknown. CFB populations were high in some corn fields this fall. If Michigan has mild winter weather, and sufficient numbers of beetles harboring the bacterium survive overwinter, growers could experience early season infection of corn seedlings in the 2007 growing season. Several predictive models based on average air temperatures during December, January and February have been developed to help determine the risk of Stewart’s wilt, but these models haven’t always proved reliable.
As overwintering beetles carrying the Stewart’s wilt bacterium emerge from the upper few inches of soil in areas near farm fields, they feed on weeds and grasses until corn seedlings emerge. Once the seedlings emerge, the beetles move to begin feeding on corn foliage, and deposit bacteria (in feces) in the feeding wounds. Repeated feeding re-infects the corn plant at additional sites, worsening the infection. Beetles that feed on infected plant tissue become carriers for the bacterium, spreading the disease even further. In the seedling stages, the bacteria produce (systemic) infections that spread through the whole plant, causing stunting, wilting or death. Stewart’s wilt is most serious when it infects corn seedlings, but can infect corn plants at any stage of development. Leaf blights, as described earlier, occur more commonly on adult plants later in the season, usually after pollination. Severe case of leaf blight can reduce yields and increase susceptibility to other diseases, such as stalk and root rots.
Unlike sweet corn, there does not seem to be much university-based research available about field corn hybrids that show tolerance to Stewart’s wilt. Field corn hybrids haven’t necessarily been selected for resistance to Stewart’s wilt, as it hasn’t been considered a problem in northern-grown hybrids. Seed corn dealers may have more specific information about which of the field corn hybrids they carry show tolerance to Stewart’s wilt.
There are no known cultural practices to reduce the disease. Seed treatments with systemic insecticides may be of benefit to reduce early season-feeding by CFB, but will not last the entire season. As mentioned earlier, whether or not Stewart’s wilt will re-appear as a problem in field corn next year is unknown. Scout fields for the presence of flea beetles soon after corn plants begin to emerge. Pay particular attention to the edges of fields adjacent to grassy areas and ditch banks, as that is where CFB will be found first, as they move from their overwintering locations. As the growing season gets underway in 2007, we’ll keep you up-to-date on CFB activity and Stewart’s wilt, through the Field CAT Alerts, and Extension web sites.
Click here to download a fact sheet about Stewart's wilt in Michigan (pdf).
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