In 2018, several tobacco crops were severely affected by bacterial stalk rot and leaf drop. This disease does not frequently occur in Kentucky tobacco, but it can result in over 50% leaf loss in the span of only a few days (Figure 1). Some 2018 crops were declared total losses due to this disease.
Bacterial stalk rot and leaf drop symptoms
Last year, symptoms appeared soon after tobacco was topped. Dark brown, elongated lesions extended from the topping wounds (Figure 2). Brown lesions also frequently appeared where leaves join the stalk (leaf axils), and leaves softened and wilted (Figure 3). Leaf veins also darkened and large sectors of leaves quickly became limp and discolored (Figure 4). After only a few days, total leaf loss in the lower half of the tobacco canopy occurred.
The bacterial pathogen Pectobacterium carotovorum causes both bacterial stalk rot and leaf drop as well as blackleg in greenhouse transplants. This pathogen is very common in the environment and has a broad host range, including vegetables, fruit, and ornamentals. The bacteria can be found relatively easily in soil, associated with crop debris, and on surfaces and equipment. The pathogen is easily spread by splashing water.
Like many other bacterial diseases, wounded tobacco tissue is more likely to be infected by (susceptible to) the stalk rot pathogen. 2018 fields with significant tobacco stalk rot issues only developed problems when significant rainfall occurred shortly after topping. No agrichemicals would be expected to be effective against bacterial stalk rot and leaf drop.
- Do not transplant into fields with significant amounts of bacterial stalk rot-affected debris, including those spread with diseased stalks
- Over-fertilization and sidedressing nitrogen applications may worsen bacterial stalk rot
- Avoid topping tobacco if heavy rain is forecasted in the next 24 hours
- Sanitize tools, equipment, and hands after working in a field with bacterial disease symptoms
- Top and harvest fields in order from least to most diseased
Emily Pfeufer, Extension Plant Pathologist