Bacterial canker, caused by the bacterium Clavibacter michiganensis subsp. michiganensis, has caused serious losses in some tomato plantings in the North Central states, including Iowa, during the last few decades. Young transplants may wilt suddenly and completely.
On older plants, leaflets begin to turn brown at the edges, then die back progressively toward the leaf midrib. Often only one side of a leaflet or a plant develops symptoms first, but symptoms eventually spread. Rarely, cavities may develop within stems, sometimes splitting open into brown, longitudinal cankers. Spots on fruit are quite distinctive: white and slightly raised at first, then raised, dark-colored centers with white halos 1 ⁄16 to 1 ⁄8 inch in diameter.
These spots are sometimes termed “bird’s-eye” lesions. The white halo turns brown as the spot becomes older. Control measures for bacterial canker are the same as for bacterial speck, except that copper sprays have minimal impact on slowing the spread of bacterial canker.
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