Pathovars (different strains with varying hosts and virulence) of Xanthomonas campestris have an extremely wide host range, including woody shrubs,vegetables, grasses, and herbaceous perennials. Seed, infected cuttings, and infected plantlets are the most likely sources of infection. Disease development is highly favored by high relative humidity, extended periods of leaf wetness, and high nitrogen levels. Sanitation is the most important disease management principle. Remove and destroy affected plants and infected plant debris. Bacteria are easily spread by water splash. Minimize splashing and reduce leaf wetness duration by watering early in the day or subirrigating. Reduce relative humidity by improving air circulation with fans, plant spacing, and by heating and venting. Do not handle plants when foliage is wet. Copper products are registered for control, but bactericides are only marginally effective in controlling bacterial diseases. Sanitation and environmental control are extremely important.
Fact Sheet: Leaf Spot Diseases on Ornamentals