Unfortunately, the oleander is not completely resistant to diseases. We show the most common diseases, their symptoms and methods of combating them.
Oleanders (Nerium oleander) are very strong and hardy bushes. In countries like the USA or South Africa, they even grow invasively and displace native species. However, in a tub or pot, where the plant has to be kept in due to the cold winters here, it is a lot more susceptible. In any case, the best precaution is that your oleander is doing well. Because a strong oleander also has a he althy immune system and is much more resilient.
If the leaves of the oleander turn yellow and fall off in summer, that's no reason to panic. Especially in the hot season, the oleander likes to carry out an all-round renewal. Although the shrub is evergreen, its leaves also have to be replaced every two years. In this case, however, new leaves should already be on the way. Other causes of yellow leaves can be lack of water or light. It is probably a disease if the leaves only change color at certain points and the yellow leaves have brown patterns. We list some of the most important diseases below.
Oleander cancer: symptoms and treatment
A common disease that can unfortunately affect all oleander varieties is the so-called oleander canker. This is triggered by Pseudomonas bacteria, which get into the sap of the plant and spread there. The result is stunted and bursting buds and flowers, often turning black. Infructescences do not develop on the affected shoots at all or only develop strangely stunted. Shoots also begin to develop outgrowths or burst open. As a result, the branches become unstable and break off.
Fighting Oleander Cancer:
- Cut back severely affected shoots.
- In the case of shoots that are not so badly infested, at least remove the infested inflorescences and fruit heads.
- Hold your cutting toolclean and disinfect it.
- Do everything you can to make your plant happy. You can find tips on how to care for oleanders here.
- Dispose of waste with household waste. In the compost, the bacteria would remain in the soil. Burning is also not an option as oleander smoke is toxic.
Unfortunately there is no treatment for oleander cancer. However, older oleander bushes in particular can cope with an infestation if you contain it through targeted pruning.
Oleander fire blight: symptoms and treatment
Fire blight is a dangerous bacterial disease that affects both fruit and ornamental crops. Since it spreads quickly and is particularly dangerous for fruit trees, there is an obligation to report this disease. Depending on the federal state, the infestation with fire blight must be reported either to the state office or to the state institute for agriculture. Information on this can be found on the websites of the state offices for agriculture in the respective states. Individual leaves and inflorescences suddenly die off starting from the stem and turn brown to black. Nevertheless, they do not fall off the plant, but stick to it. If you don't take any action, the plant will die within a few weeks.
Fire blight control measures on oleanders:
- Cut back infested parts rigorously.
- Dispose of the resulting green waste well packaged in the household waste; under no circumstances throw it in the compost bin or on the compost.
- Disinfect your cutting tools thoroughly with high-proof alcohol.
- Immediately separate the infested oleander from other fruit or ornamental trees in the area.
- Preparations containing microorganisms can help control and prevent fire blight.
Oleander dry rot: symptoms and control
Blight is caused by a Ascochyta fungus. Paradoxically, the reason is usually too high humidity or too much water from above. The oleander is particularly infested in the winter quarters, but rainy summers can also become a problem. In particular, dense oleander bushes that dry off poorly are vulnerable.
Symptoms are brown and black spots on shoots and leaves. Particularly delicate parts of the plant are attacked first. Once againAs the name “dry rot” already suggests, affected areas appear dried out. The fungus gradually migrates to the base of the plant. Once it has reached this, the oleander dies.
Measures to combat dry rot in oleanders:
- Infestation with dry rot can be prevented with fungicides.
- Cut off affected branches and shoots rigorously to the nearest unaffected fork; cut down to the he althy wood; spreading to the base must be prevented at all costs.
- Pay attention to the hygiene of your cutting tools.
- Dispose of affected shoots in the household waste.
Gray mold on oleanders: symptoms and control
The gray mold is less dramatic. It also occurs as a result of high humidity, i.e. in rainy summers or in winter quarters. However, mainly double-flowered species are affected, as they do not shed their flowers themselves. Therefore, remove all dried flowers from the shrub before putting them into winter quarters and during long periods of rain. Gray mold affects only the bud sites and does not pose a serious threat to the plant itself. However, it can ruin next year's flowering.
Powdery mildew on oleander: symptoms and control
Powdery mildew is what is called the phenomenon when black deposits form on the leaves of the plant. In itself, however, sooty mildew is not a disease, but a consequence of aphids or scale insects. The transparent and sticky honeydew they secrete is colonized by fungi and turns black. This hardly harms the plant directly. However, the black discoloration impedes photosynthesis in the affected leaves and clogs the pores. However, sooty mildew can be easily wiped off with water. In stubborn cases, a highly diluted vinegar solution can also be used. However, you should take care of the lice seriously, because they can cause great damage.
Find out here which pests occur on oleanders and how to deal with them.
To prevent diseases, proper care of your oleander is particularly important. In this article you will learn the most important thing about this topic.