As far as oleander diseases go, oleander knot diseases aren’t the worst. In fact, although it can cause plant dieback, oleander knot generally doesn’t result in long-term damage or death of the plant. However, the warty galls cause unsightly, distorted growth. If oleander knot disease has afflicted your oleander plant, read on to learn about treating the disease, also known as nerium canker.
What is Oleander Knot Disease?
Oleander knot is the result of a type of bacteria (Pseudomonas syringae pv. Savastanoi) that enters the oleander plant through wounds and injured or scarred areas. The bacterium is systemic, resulting in the development of knots or bacterial gall on oleander flowers, leaves and stems; and stunted, deformed seed pods. The disease is widespread in Arizona and other areas where oleander plants are popular.
Oleander knot disease is most common after cool, damp springs. The bacteria requires a wound to enter the plant and often finds a convenient route through areas affected by winter damage, or by improper pruning. It also spreads by contact with contaminated water, infected garden tools, or even human hands.
Treating Nerium Canker
Prune infected plant parts, but only when the foliage – and the weather – is dry. Treat the pruned area with a 10 percent bleach solution to prevent entry of the bacteria. Wipe pruning tools with rubbing alcohol or a bleach solution between each cut, and after the job is completed. You can also use a commercial disinfectant, applied according to label recommendations.
Water oleander bushes carefully at the base of the plant to keep the foliage dry. Avoid watering with sprinklers, which can spread the pathogens to uninfected plants. Overhead watering is especially risky after pruning an oleander.
If the infection is severe, apply a copper fungicide or a Bordeaux mixture in autumn. Continue to spray periodically when new growth emerges in spring.