Mottled, brown or yellow leaves can indicate various causes for rhododendrons. In many cases, a fungus is responsible for the damage. So that it does not spread in the first place, the choice of location and balanced care are of great importance.
Diseases can often be recognized by the leaves
These are common fungal diseases:
- powdery mildew: caused by fungal species such as Erysiphe cruciferarum, Sphaerotheca pannosa or Microsphaera alni
- leaf spot disease: Collective term for species such as Glomerella, Cercospora, Pestolotia and Colletorichum
- Rhododendron Rust: arises from different species of the order Pucciniales
- bud dieback: as a result of infestation by Pycnostysanus azaleae
- dieback: caused by Verticillium dahliae and albo-atrum
powdery mildew
This fungus causes a grayish, mealy coating that covers the leaves and stems. Insufficient ventilation and warm and dry conditions favor the growth of the spores. Cut out the affected areas generously and spray an 8:1 aqueous milk solution all over the plant. After an exposure time of 20 minutes, rinse off the residue. Repeat the treatment two to three times. The lecithin contained in the milk kills the fungal spores.
leaf spot disease
There are more than 20 different types of fungi that can cause this condition. They spread in humid weather, causing patchy discoloration, which, as it spreads, leads to leaf loss and stunted growth. To prevent an infestation, you should choose the location for the rhododendron favorably. Do not put the ornamental shrub in too shady areas.
Rhododendron Rust
Rust fungi rarely occur on rhododendrons and cause yellowish to orange spore deposits on the underside of the leaves. They are easily confused with leaf spot disease, as this manifests itself in different discolorations. To prevent fungal infestation, you should fertilize the ornamental shrubs regularly and water them at the base of the plant.
bud dieback
Small injuries in the plant tissue create entry points for fungal spores. Typical are brown discolored buds that wither over the winter. Evergreen varieties are more likely to be affected by this condition. In March, cut out all dead plant parts and strengthen the plant with liverwort or algae extracts. Since this fungus is believed to be transmitted by the rhododendron planthopper, you should combat this pest.
dieback
Azaleas are often affected by this disease, in which first the leaves and later the shoots droop. The fungus clogs the pathways so that the plant can no longer take care of its foliage. Spraying with manure from field horsetail, wormwood, comfrey, tansy or nettles strengthens the plant. Once the fungus has settled in the roots, the perennial can no longer be saved and must be cleared.
tips
This disease is known by various names such as Phytophthora or Verticillium wilt. However, the damage patterns and methods of combating them do not differ.