Oleander with its delicate flowers and shiny foliage is an ornament for every garden - but is also quite sensitive to various pests and diseases. These preferably occur towards the end of winter, as the plant is very weakened and therefore vulnerable due to the lack of light. For example, gray leaves are often observed on overwintered oleanders, which can have various causes.
What causes gray leaves on oleanders?
Gray leaves on oleanders can indicate spider mite infestation or fungal infections such as mildew or gray mold. Repeated showering and an airy location are helpful against spider mites. A milk-water mixture helps with mildew; with gray mold, faded flowers should be removed.
Gray, stunted leaves indicate spider mites
Stunted leaves with a grayish-white coating are often the result of a pest infestation, most often spider mites. As soon as the leaves look like this, the infestation is already very advanced - they have been damaged by the insects' sucking behavior and will no longer regenerate. Remove the leaves and shower the oleander with a sharp jet of water. Repeat this procedure again and again and also place the plant in a draughtier location - spider mites love warmth and dryness, which is why they are very sensitive to regular showers and an airy place. In addition to spider mites, pests such as the red spider or thrips also cause the damage described.
Fungal diseases often possible cause
Oleander is also extremely sensitive to various fungal infections. In many cases, gray leaves are also the result of an infestation with powdery mildew or gray rot (gray mold).
Mildew
The expert summarizes two different clinical pictures under the term “mildew”. The so-called powdery mildew causes a disease with leaves covered with a mealy, gray-white coating. This disease, which is quite common in oleanders, is caused primarily by excessive humidity. The host fungus deprives the plant of valuable nutrients, so that growth stalls and the oleander only produces a few flowers. It is helpful to treat with a milk-water mixture (mix whole milk and water in a ratio of 1:10), which you can distribute generously on the affected parts of the plant using a spray bottle. Repeat the process several times at intervals of a few days and weeks.
Grey mold (Botrytis)
Gray mold occurs primarily on double-flowered oleanders; varieties with single flowers are almost never affected. To prevent this, you should pick off the faded flowers before putting them away for winter quarters and thus deprive the fungus of any food source - it settles on the flowers first.
Tip
To avoid infestation with pests or fungi, you should put the oleander into winter quarters as late as possible and clear it out again as early as possible.