The following is information on bacterial leaf spot of Zinnia, a disease present in landscapes at this time.
Bacterial leafspot on Zinnia has been evident in gardens for several weeks. Look for small angular brown spots with yellow borders on lower leaves. It can spread quickly with wet weather. The disease will move higher on the plants and make them look poorly by fall. There is no effective control at this time. Copper fungicides/bactericides may cause some reduction or halt spread if applied now. Be sure to check the label for safe times to apply. This bacteria can overwinter in old infected leaf tissue and is seed-born, which is the primary source of infections we see. Greenhouse growers should make efforts to eliminate this disease before plants are sold. Suspect plants should be destroyed. Protective sprays of copper may be needed if this is a persistant problem in greenhouse plant production, but be careful with rates to avoid copper injury to plants.
Bacterial leaf spot of Zinnia. Photo by Bob Mulrooney, UD.
Adapted from an article by Bob Mulrooney, Extension Plant Pathologist, UD.