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Issue No. 1, Article 4/March 18, 2004

Warmer Winter for Corn Flea Beetles: Early-Season Stewart's Wilt Predictions

Variable winter temperatures across the state have resulted in varying predictions of Stewart's wilt in corn this spring. Overall, the average winter temperatures of December, January, and February were warmer than the average winter temperatures of the previous year. What does this mean with respect to corn flea beetles and Stewart's wilt?

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 beetles, increasing the potential for Stewart's wilt, which can be predicted using the average temperature of December, January, and February (Table 1).

Corn flea beetles become active in the spring when temperatures rise above 65°F. The beetles feed on and infect seedling corn plants. The bacterium can spread systemically throughout the plant. 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 and die. Infections of older corn plants usually result in development of the leaf blight phase of Stewart's wilt, characterized by long, yellow to chlorotic streaks, with wavy margins along the leaves. 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.

Table 2 shows estimates of early-season Stewart's wilt based on the recent winter temperatures from the Midwest Regional Climate Center. 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 in the corn flea beetle fact sheet (http://www.ipm. uiuc.edu/fieldcrops/insects/corn_flea_ beetle/index.html) and the sweet corn disease nursery (http://sweetcorn.uiuc. edu/stewarts.html).--Kelly Cook

Kelly Estes

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