Bacterial soft rots, leaf spots, blights, wilts—Erwinia,
Pseudomonas, Xanthomonas spp.
Bacterial soft rots affect many plants including begonia,
carnation, daffodil, geranium, impatiens, and zinnia. Soft
rot bacteria cause infected tissue to turn brown, become
mushy, and develop an unpleasant odor. Stem tissue turns
brown and deteriorates near the soil. Plants grow slowly
and seedlings collapse. Bacterial spots often start out as
tiny water-soaked areas on leaves, stems, or blossoms. Spots
or blotches turn dark gray or blackish as they enlarge and
sometimes have yellow borders. Initial spots are circular
but may become angular and coalesce and cause plant tissue
death or necrosis. Cankers may form on stems. Under wet conditions,
infected tissue may exude brownish masses of bacteria. Dead
tissue may tear out, leaving holes and a ragged appearance.
Pathogens causing spots, blights, and soft rots can also cause
vascular wilt if the infecting bacteria become systemic. Aboveground
plant parts yellow, droop, wilt, and die.
Solutions
Use disease-free cuttings, corms, and other
stock. Avoid planting too deeply. Provide good drainage. Do
not overwater and avoid overhead irrigation. Keep foliage
dry and provide good air circulation. Don’t crowd plantings.
Bacteria commonly infect through wounds, so avoid injuring
plants. Use good sanitation. Regularly inspect plants for
disease and remove infected plants immediately. Some cultivars
are more susceptible to infections than others. Seek information
on resistant cultivars and consider planting them.
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Wilted lilac leaves and blossoms caused by Pseudomonas bacterial blight
Bacterial leaf spot on Geranium
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