Symptoms and Signs
Initial symptoms of bacterial leaf spot consist of water-soaked, irregularly shaped spots that measure 0.12 to 0.25 inch in diameter. As the disease develops, these small spots enlarge to as much as 0.5 to 0.75 inch in diameter, are angular in shape, and turn dark brown in color. Occasionally, spots have black sections or edges, or they may have faint yellow halos. On leaves with numerous spots, the spots sometimes merge together, resulting in the death of large areas of the leaf. Spots are visible from both top and bottom sides of leaves. The disease occurs on both newly expanded and mature foliage.
Comments on the Disease
Bacterial leaf spot of spinach is not common in California. When present, the problem is always associated with overhead sprinkler irrigation and rainy springs. A similar spinach disease has previously been reported in Italy and Japan. This pathogen is an aerobic, gram-negative bacterium; on microbiological media it produces cream-colored colonies that are typical of most pseudomonads. Strains are non-fluorescent when cultured on Kings medium B. The pathogen appears to be host specific to spinach, and weed or other reservoir hosts have not been identified. The pathogen is likely seedborne.
Because the disease is uncommon, a management program is not necessary. If the disease occurs, avoid using overhead sprinklers.