Stewart's wilt

Taxonomic position and nature of the pathogen. Xanthomonas stewartii (commonly accepted scientific name Pantoea stewartii) is a Gram-negative bacterium classified within the Erwiniaceae family. It functions as a systemic vascular pathogen, specializing in colonizing the xylem of host plants and causing significant physiological disruption.

Diseases and host plants. The bacterium is responsible for Stewart’s wilt of maize. It primarily affects sweet corn, though field corn and popcorn varieties can also be susceptible. Infected plants display characteristic long, wavy-edged yellow streaks on the leaves that eventually lead to leaf necrosis, vascular wilting, and potential plant collapse during early growth stages.

Biology and life cycle. The transmission of the pathogen is intrinsically linked to the corn flea beetle (Chaetocnema pulicaria). The bacteria survive the winter months within the adult beetles. As spring approaches and temperatures rise, beetles feed on young corn seedlings, transferring the bacteria into the plant's vascular system, where they multiply rapidly and clog the xylem vessels.

Conditions for spread and economic impact. The incidence of the disease is highly correlated with winter temperatures; mild winters ensure a higher survival rate for flea beetle populations, increasing the risk of early-season infection. The economic impact is severe, particularly for sweet corn, where infection can result in total crop loss, stunted growth, or poor grain development.

Control and management measures. Managing Stewart's wilt requires an integrated pest management (IPM) approach:

• Planting corn hybrids that possess genetic resistance to the disease.
• Scouting for corn flea beetles and applying foliar insecticides when populations exceed threshold levels.
• Removing volunteer corn and weeds that act as alternative hosts.
• Monitoring weather patterns to forecast the risk of beetle survival and potential outbreaks.