Diseases of oleander (
Oleander gall
Oleander gall is caused by the bacterium Pseudomonas syringae pv. savastanoi. The bacterium is systemic in the plant, and causes galls to form on flowers, leaves and stems. The bacterium must have a wound site to enter the plant, and freeze damage to flowers in early spring after a rain is a common circumstance under which infection takes place. The bacterium enters through the damaged flowers and galls form on the inflorescences (photo 1). Severe infections are most common after a cool wet spring.
Bacterial gall normally will not kill the plant. Infected plant parts can be pruned, but care should be taken not to disseminate the bacterium on pruning tools. Prune infected tissue well below the infection site, at least a foot if possible, and disinfect pruners between cuts by dipping them in a 10% bleach solution (common household bleach at 1:10 dilution) for a short time (be sure to rinse the bleach off the tools when you are finished, perhaps even spray with a lubricant to avoid oxidation of the metal).
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February 21, 2013