Bacterial leaf spot
Pathogen: Pseudomonas spp., Xanthomonas spp.
Hosts Include: Astilbe, Chrysanthemum, Delphinium, Echinacea, Heuchera, Hypericum, and Rudbeckia.
Symptoms: Disease symptoms include water soaked lesions on foliage that darken with age. Lesions may be bordered by the leaf veination.
Spread: Bacteria on the plant surface are easily spread by splashing water from rain and irrigation to nearby plants. Asymptomatic plants can serve as a source of inoculum.
Management: Bacterial pathogens can survive and reproduce on the surface of asymptomatic plant tissues. Disease symptoms develop once the pathogen reaches high population levels on the plant surface. Sanitation is especially important for bacterial pathogens. Workers should wash their hands after handling diseased plants. Foliage should not be handled when it is wet. Symptomatic plants should be destroyed. Avoid over head irrigation, or time irrigation to minimize leaf wetness. Succulent tissue is especially susceptible to infection. Most fungicides are not effective against bacteria. Copper-based products are helpful in limiting populations of surface borne populations of bacterial pathogens.