As discussed in issue no.1 of the Bulletin, corn flea beetle activity was expected to be low in much of Illinois; southern Illinois generally has mild enough winters to allow survival of the corn flea beetle. With that in mind, it is always important to keep an eye out on seedling corn.
Kevin Black, with Growmark in Bloomington, shared a report from Alan Mosler, seed sales agronomist at Southern FS, who found 8 to 10 flea beetles per seedling corn plant on 2-leaf-stage corn in Franklin County.
Flea beetles overwinter as adults and become active when spring temperatures increase to 65° to 70°F. Although they prefer to feed on corn, flea beetles will also feed on several other hosts, including orchard grass, Kentucky bluegrass, fall panicum, crabgrass, redtop, witchgrass, foxtail, Sudan grass, barley, and wheat. As corn begins to emerge in the spring, they move from these secondary hosts to cornfields. When scouting seedling corn, look for corn flea beetles and symptoms of the injury they cause. Feeding appears as scratches on the corn leaves and rarely causes economic damage unless densities are very high. Corn flea beetles also transmit the bacterium Erwinia stewartii, which causes Stewart's wilt. Seedling corn infected by Stewart's wilt may have yellow, linear lesions on the leaves, become stunted, and wilt.
Corn flea beetles feeding on seedling corn.
Sweet corn hybrids and seed corn inbreds are more susceptible than most dent corn hybrids to flea beetle injury and Stewart's wilt. Most commercial field corn hybrids are resistant to the wilt phase of Stewart's wilt after they develop beyond the 5-leaf stage. Although some hybrids remain somewhat susceptible to the leaf blight phase of Stewart's wilt, it does not occur at or after tasseling in dent corn. Treatment of seedling corn plants is recommended only when seedlings are severely damaged and plants are being killed. Insecticide recommendations for rescue treatments may be found in the Illinois Agronomy Handbook (http://web.aces.uiuc.edu/aim/IAH/ch18/).--Kelly Cook