Issue No. 1, Article 4/March 16, 2005
Winter Temperatures Predict Promising Year for Corn Flea Beetles
Average winter temperatures in Illinois were approximately 5 degrees warmer than they were a year ago (Figures 1 and 2). These warmer temperatures during the months of December, January, and February favor increased survivorship of the corn flea beetle and the bacterium it vectors.
LEFT: Average Temperature in Degrees F, December 1, 2003, to February 29, 2004. RIGHT: Average Temperature in Degrees F, December 1, 2004 to February 28, 2005.
Figures 1 and 2. Average winter temperatures of 2003-2004 and 2004-2005. Source: Midwestern Regional Climate Center, Illinois State Water Survey.
Corn flea beetles are the primary vector of Stewart's wilt. Erwinia stewartii, the bacterium that causes Stewart's wilt, survives the winter in the gut of the corn flea beetle. Survival of the corn flea beetle is dependent on winter temperatures. Warmer winters result in greater survivorship of corn flea beetles, thus increasing the potential for Stewart's wilt. Using the average temperature of December, January, and February, the potential of Stewart's wilt can be predicted (Table 1).
Corn flea beetles become active in the spring when temperatures rise above 65°F. Corn flea beetles feed on and infect seedling corn plants. The bacterium can spread systemically throughout the plant. Although most commercial field corn hybrids are resistant to Stewart's wilt, the disease is still a concern for susceptible seed corn inbreds and sweet corn hybrids.
Warmer winter temperatures bode well for corn flea beetles this year.
There are two phases of Stewart's wilt: the seedling wilt phase and the leaf blight phase. The seedling wilt stage occurs when seedlings become infected at or before the V5 stage. The growing point is easily infected. The vascular system becomes plugged with bacterium, causing the seedling to wilt, become stunted, and die. Infections of older corn plants usually result in the development of the leaf blight phase of Stewart's wilt. This phase is characterized by long, yellow-to-chlorotic streaks, with wavy margins along the leaves. The late infection phase, or "leaf blight phase," of Stewart's wilt occurs after tasseling and is generally not a concern in sweet corn because ears are harvested before damage occurs.
Based on the recent winter temperatures from the Midwest Regional Climate Center, estimates of early-season Stewart's wilt are shown in Table 2. Remember, however, that these are only predictions; numbers of surviving corn flea beetles are not known. More information on the corn flea beetle and Stewart's wilt can be found on a new corn flea beetle fact sheet (Adobe PDF) and the sweet corn disease nursery Web site.--Kelly Cook