Description and Symptoms
Stewart’s disease (Pantoea stewartii) is no longer common in cornfields, primarily because of the use of neonicotinoid seed treatments that control the vector, the corn flea beetle (Chaetocnema pulicaria). Stewart’s blight lesions spread from flea beetle feeding scars (a tiny scratch on the leaf) and are initially pale green to yellow streaks, later becoming brown as tissue dies. The margins of the streaks are usually wavy but generally follow leaf veins. If stalk infection occurs, the entire plant will wilt. When cut, infected stalks may ooze droplets of pale yellow bacteria. Most hybrids are resistant enough that no further management is required. Cultural practices and fungicides are not effective against this disease. Systemic insecticides applied to the soil or seed can be used to manage corn flea beetles and, consequently, Stewart’s disease.
The best time to scout for Stewart's disease is when the corn flea beetle feeding is apparent from VE toV5 (Stewart's wilt) and again after R1 (Stewart's leaf blight). It is often confused with northern leaf blight and Goss's wilt.
The environment to look for Stewart's disease in is warm air temperatures in December, January, and February. These warm temperatures increase corn flea beetle survival and result in greater transmission of the bacterium the following season.
Photo by Gary Munkvold