WSU Extension

Hortsense

Geranium : Bacterial blight
(revision date: 4/23/2014)


Use Integrated Pest Management (IPM) for successful plant problem management.

Biology
Bacterial blight (leaf spot and stem rot) arises due to a bacterium that can survive in soil for more than 6 months. These bacteria cannot survive in soil after the plant decomposes. They are readily spread by physical contact, irrigation water, rain, tools, and insects. Bacteria are not contained in seed. Sudden black rotting may start at the base of cuttings, and blue-black rotting emerges on stems. Leaves drop, then stems partially recover and produce new leaves at the terminals. Depending on the variety, either round spots or angular dead areas develop on leaves. Spots initially appear as translucent pustules similar to those of oedema. Round spots are dark green to black, about 0.1 inch in diameter, and sunken. The arrival of angular dead areas is often accompanied by the wilting of leaf edges. Ivy geranium foliage loses luster and shows symptoms suggesting nutrient deficiency or mite infestation. Some regal or Martha Washington cultivars are extremely resistant, although leaf spots have been observed. Hardy, perennial geraniums can be carriers of the bacteria without showing any symptoms.
Management Options

Non-Chemical Management
  • Reduce spread of the disease by disinfecting pruning and other tools often.
  • Increase spacing between plants to reduce water splashing from plant to plant spreading disease.
  • Remove and destroy infected plants.
Select non-chemical management options as your first choice!

Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

Focus on cultural methods. Pesticides are not recommended to manage this disease in home situations.

Images
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Caption: Geranium stem rot
Photo by: R.S. Byther
Caption: Bacterial leaf spot on geranium
Photo by: R.S. Byther