Caused by: Xanthomonas campestris pv. pelargonii

Hosts: Pelargonium x hortorum, Pelargonium peltatum, Geranium spp. (especially Geranium sanguineum), and (rarely) Pelargonium domesticum.

Danger: disease is highly contagious: will spread from hanging baskets to bench-level crops, from vegetatively-propagated to seed-grown geraniums, & from cultivar to cultivar by splashing, handling, or root-to-root transmission via capillary mats, etc.

Defense: ï purchase cuttings from reliable propagator
ï keep batches from different propagators separate
ï keep cultivars separate (with sanitation practices)
ï keep seedlings separate from zonals
ï grow ivy baskets over crops other than zonal geraniums
ï scout

Symptoms: small, round, brown spots, 1/16-1/8 inch in diameter (these symptoms are less common during the fall & winter than in spring)
leaf chlorosis (yellowing)
leaf necrosis (dry, brown leaves)
necrotic leaf wedges
leaf wilting
healthy-looking roots, even though plants show symptoms of water stress
total plant wilt
stunting

Response: ï obtain lab diagnosis (easy to mistake for other, less serious diseases)
ï rogue out diseased plants and those adjacent
ï continue to scout and rogue
ï copper sprays (e.g. Phyton 27, Kocide 2000 T/N/O) will reduce bacterial populations on plants and bench surfaces, but cannot cure diseased plants
ï at end of season, clear out geraniums and geranium debris, sanitize surfaces with disinfectant, and wait as long as possible before reintroducing geraniums for the next crop cycle

Note: Ralstonia (=Pseudomonas) solanacearum, which causes a disease of many plant species called Southern bacterial wilt, will cause yellowing, wilting and collapse of geranium leaves that closely resembles systemic symptoms of bacterial blight caused by Xanthomonas pelargoniióBUT Southern bacterial wilt does not cause leaf spots. ELISA tests and/or culturing in a laboratory may be used to separate the two diseases.