Luring June and August, when the newly emerged adults appear, the leaves of corn may be partly covered with their feeding scars. During the feeding process, the adults disseminate a bacterial wilt of corn called Stewart's disease . This disease infests the water-conducting tissues of the plant. Generally, field corn infested with Stewart's disease will show little sign of disease until late in the summer when numerous leaf lesions will appear on the leaves. However, in years when flea beetles are abundant and the disease is widely disseminated, some varieties of corn will wilt and the plants may die before tasseling.
Drought can aggravate or accentuate the diseased condition of a plant.
The result is often small ears or no ears at all. When conditions are favorable for both the beetles and the wilt, nearly 100 percent of the susceptible varieties of field corn will show symptoms of Stewart's disease by late fall. Evidence of Stewart's disease is more common and the results more drastic in sweet corn than in field corn. A large percentage of sweet corn plants infested in the seedling stage will die or dwarf and produce no harvestable ears. Plants not showing these drastic effects may produce normal ears if they get plenty of water.