Issue No. 1, Article 5/March 24, 2006
Another Warm Winter, Another Year of Corn Flea Beetles?
Average winter temperatures in Illinois are very similar to those of one year ago (Figures 1 and 2). These warm temperatures during the months of December, January, and February favor increased survivorship of the corn flea beetle and the bacterium it vectors. 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 temperatures 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.
There are two phases of Stewart's wilt: seedling wilt and leaf blight. 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 tempera-tures from the Midwest Regional Climate Center, estimates of early-season Stewart's wilt are shown in Table 2. Degree-day accumulations can be found using the Degree-Day Calculator. Remember, however, that these are only predictions; numbers of surviving corn flea beetles are not known. However, with high populations in 2005 and the warm winter months, spring populations look to be high. Be sure to get out and scout seedling corn. More information on the corn flea beetle and Stewart's wilt can be found on the corn flea beetle fact sheet (Adobe PDF) and the sweet corn disease nursery Web site.--Kelly Cook