Based on temperatures this winter, five Ohio State University Extension specialists predict that the risk from Stewart’s wilt this season will range from low to high, depending on where you grow sweet corn in Ohio.

The specialists are Ron Hammond, Pierce Paul, Andy Michel, Dennis Mills and Bruce Eisley.

The average temperatures during December, January and February give an indication of populations of adult corn flea beetles—the insect that carries the bacterial leaf blight—will be during the spring. Adult flea beetle survival is much greater during mild winters than during cold ones.

Flea beetles become active in the spring when the soil temperatures reach 65 degrees Fahrenheit. Adults are most active on sunny, warm, windless days.

If the adult fed on diseased corn in the late summer or fall, it may carry the bacterium that causes Stewart's disease of corn in its gut over the winter. In the spring as the corn emerges, the flea beetles feed on the young plants and spread the bacterium which in turn causes seedling wilt and leaf blight.

The occurrence of Stewart's bacterial disease depends on the level of bacteria-carrying flea beetle survival over the winter.

For many years the winter temperatures have been used to predict the risk of Stewart's disease because higher populations of the flea beetle survive during mild winters than during cold winters.

The “flea beetle index” is calculated as the sum of the average temperatures (Fahrenheit) of December, January and February.

♦ Index values less than 90 indicate negligible disease threat,

♦ 90-95 indicate low to moderate levels,

♦ 95-100 indicate moderate to severe and

♦ values over 100 predict severe disease threat.

The five specialists checked the average temperature for those months at several locations in Ohio to determine the risk level for 2008, according to the flea beetle index for 2008. The locations and the corresponding indexes were:

♦ Hoytville, 84.4;

♦ Wooster, 88.4;

♦ Ashtabula, 87.4;

♦ South Charleston, 90.4;

♦ Jackson, 99.7; and

♦ Piketon, 100.3.

These numbers would indicate that the risk of Stewart's bacterial leaf blight is low to moderate in northern and west central Ohio with a higher disease risk in southern Ohio.

These values are very similar to those from last winter, 2007.But when you compare the temperatures last year to the past three months, we see a very different picture. Last year, December and January were relatively warm, while February was an extremely cold month.

This year, these three months have, on average, been more typical of the temperatures you’d expect, without any month being neither extremely warm nor cold.

Even if you plant a hybrid that is less susceptible to Stewart’s wilt, the five specialist still recommend scouting for flea beetles.

If you want to take preventive action against flea beetle, a commercially applied insecticide seed treatment, such as Cruiser or Poncho, is labeled for flea beetles.

For more information on Stewart's wilt, visit the Ohio Field Crop Disease Web site.

To subscribe to the print version of The Grower, click here.