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Oleander Diseases

The oleander is a naturally robust plant. Nevertheless, it is not immune to diseases that can seriously damage the shrub. Therefore, early detection and the right treatment are important.


Oleander diseases are caused by viruses, bacteria and fungi. Their origin cannot usually be determined, but the damage they (can) cause is all the greater. The diseases that oleanders most commonly suffer from are:

  • Oleander canker: Pseudomonas bacteria
  • Dry rot: fungal disease
  • Gray mold: fungal disease
  • Sooty mildew: fungal disease

oleander crab

Oleander canker is the disease that not only bothers the oleander the most, but also affects it most frequently. Protection against the Pseudomonas bacteria is almost impossible because they are ubiquitous in nature. That's why they willpuddle germs" called.

Infection with the disease begins when the bacteria enter the sap stream of the oleander. Externally, signs appear only in the course of the infection. The first symptoms that you can recognize appear on flowers, buds and leaves. If you see the following damage picture, then the plant is suffering from oleander canker:

  • Buds: thicken, turn black, burst
  • Flowers: do not develop or develop stunted petals
  • pedicels: burst open lengthwise

As the disease progresses, cauliflower-like growths develop on the branches. In the final stages of the disease, the branches and shoots are torn and covered with growths. This causes shoots to break off, leaves and flowers curl up and fall off. The seed pods burst open too early and fall off as well.


There is a remedy for almost every disease. Unfortunately, the oleander canker is not one of them, because so far it has not been possible to find a remedy that defeats the cancer. Pruning the oleander can prolong its life, but it does not cure it.


Liberally cut off any part of the plant showing symptoms of the disease. Don't be afraid to cut into the old wood. Since cutting off the parts of the plant reduces the infestation pressure for the oleander, it closes the gaps that have arisen.

tip: You can repeat this form of treatment more often. However, the diseased oleander will eventually lack the strength to close the gaps. Never dispose of the clippings in the compost, the bacteria will find their way back into the garden. It is best to put the clippings in the household waste, well sealed.


The fungal disease Ascochyta (dry rot) is caused by a sac fungus caused. Since the fungus can affect all parts of the plant, dry rot also occurs on all parts of the plant. If the fungal infection is not recognized and subsequently not treated, it can lead to the death of the oleander. You can recognize the dangerous fungal infection by the following symptoms:

  • Flowers appear to dry up and fall off
  • Formation of dry zones on different parts of the shoot
  • Dying off of the areas above the dry zones


Unlike oleander canker, you can win the battle against dry rot. However, this is only possible if the disease has not yet passed old wood has advanced. If this has already happened, the death sentence for the oleander is certain.


Cut out the affected parts generously from the bush. This will prevent the fungal spores from spreading to the base of the plant. You should definitely check the interfaces to seal, preferably with a preparation that contains a fungicide to prevent the fungus from entering the oleander through the open areas. After cutting, treat the plant with a fungicide. The clippings must not be disposed of in the compost, but should be disposed of with household waste.

tip: Also spray neighboring oleander plants as a preventive measure.


The fungal infection most commonly occurs in the fall or during the wintering of the oleander. You should therefore make sure that the winter quarters are not too damp. You should also refrain from pruning the plants in autumn, i.e. before moving to the winter quarters, as the open cuts are the ideal gateways for the fungus.

tip: Infection can occur in summer when the weather is cool and rainy.

gray mold

Gray mold only forms on the flowers of the oleander. The fungal pathogen Botrytis is responsible for the infestation. It prefers to attack oleander plants that have double flowers. That's why you should regularly remove faded flowers by hand. You can recognize an infestation by the fact that the flowers look moldy.


If gray mold has formed, the affected flowers or shoot tips must be removed immediately so that the infection cannot spread further. After that, spray the oleander with a fungicide.

tip: Gray mold tends to appear during overwintering when the winter quarters are warm and humid. Therefore, you should air the winter quarters regularly.

sooty mildew

This fungal disease often develops in the course of infestation with aphids, since the sugary honeydew that the insects excrete serves as food for the fungus. Sooty mildew is easy to recognize because the leaves are covered with a black coating when infested.


First and foremost, you should fight the lice so that the fungus is deprived of its food source or does not even establish itself. If the plant has been infected, wash off the fungus with a rag or brush, or cut off the infected areas.

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