Oleander is known to be very susceptible to certain diseases and pests. Some diseases can hardly be avoided, no matter how hard you try, because they are simply present in almost every oleander and break out quickly under the right conditions. This type of oleander disease includes oleander canker, caused by the bacterium Pseudomonas, the first signs of which are often brown to black spots on the undersides of the leaves.
Too much moisture can cause fungal infections
fungal infection
However, you do not have to fear the worst with every black spot, because in many cases black leaves are an indication of a harmless fungal infection. This occurs particularly often when the leaves of the oleander get wet and cannot dry off quickly enough or when the oleander stands in a cool place with high humidity for too long. For this reason, such black spots often appear during or after the shrub has overwintered.
- First collect infested leaves and dispose of them with household waste (do not put them in the compost!).
- Monitor the diseased oleander and isolate it from other plants.
- Provide a dry and warm location.
- Cut back the shrub only when the fungus has spread to the shoots as well.
- Treat the oleander with a fungicide if the infestation is severe.
Scale or aphid infestation
If you can easily wipe the black off the leaves with your fingers, it's probably a sooty mold fungus. In almost all cases, this is an indication of a pest infestation, primarily by aphids or scale insects. Both insects secrete a sweet secretion (the so-called "honeydew"), which in turn serves as food for the sooty mold fungus. In order to be able to combat the sooty mold fungus effectively, you must also put an end to the pests that cause it. So if you make sure that scale insects and aphids no longer feel too comfortable on your oleander, then the sooty mold fungus will soon be history too.
Oleander crab (Pseudomonas)
Oleander canker is often manifested by knobbly growths on the shoots and black or dark leaf spots surrounded by a light border. This disease is caused by Pseudomonas bacteria and spreads quickly. The disease is not necessarily fatal, but can only be treated with vigorous pruning.
tips
If you are unsure of the cause of the black leaf spots, wait and watch the oleander - you can always cut it off if the worst comes to the worst.