An ivy geranium was diagnosed with bacterial blight at the UMass Extension Plant Diagnostic Lab this week. Bacterial leaf blight of geranium is caused by Xanthomonas hortorum pv. pelargonii. Symptoms include chlorosis and eventual necrosis of leaves. The bacterium can also become systemic in geranium and cause stunting, wilt, and decline. Bacteria are easily spread by splashing water and reproduce rapidly in warm, humid conditions.
Management: Since plants may have been infected in the propagation facility, contact your supplier. Scout all geranium crops frequently for symptoms and discard infected plants. Clean and disinfect potting areas and benches thoroughly. Workers should wash their hands frequently, especially after handling diseased plants or soil. Handling of wet foliage should be avoided. Since bacteria can be spread from plant to plant by irrigation water, minimize splashing and reduce leaf wetness by spacing, improved air circulation with fans, and sub-irrigating where possible. Some copper products are registered for the control of Xanthomonas on several greenhouse crops: see the New England Greenhouse Floriculture Guide for more information. Bactericides are only marginally effective in managing bacterial diseases, so sanitation and environmental control are crucial for successful management. Sprays may help protect uninfected plants but will not cure an infected plant.
- Dr. Angela Madeiras, Extension Educator & Diagnostician, UMass Extension Plant Diagnostic Lab