Bacterial Canker

Clavibacter michiganensis

This seed borne bacterial disease of tomatoes isn’t very common. Seedlings growing from infected seed may be killed immediately, they may be weak and stunted, or they may appear normal and only exhibit disease symptoms at a later date (even when flowering). Symptoms of this kind of systemic infection include wilting, curling and browning of leaves (this may be in all or part of the plant). Even after the leaflets die the petiole (stem) usually stays green. There may also be characteristic dark, water-soaked open cankers on the stem (which is where the disease gets its name). These exude bacteria that can easily spread to nearby plants. The inside of the infected stem will be reddish brown in color rather than green.

If the plant gets infected from an external source, the first symptoms to appear are on the surface and may include scorching of the leaves, as well as slightly raised circular white spots or small necrotic lesions on leaves or fruit.

Bacterial canker can survive in the soil, on plant debris and on solanum family weeds. It can be spread to your plants by rain, wind, people, tools and by staking and pruning. Keep the beds clear of plant debris, rotate your crops and remove and destroy infected plants. Because bacterial canker is commonly seed borne it is important to use disease free seeds.

Image: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org