Home generalRhododendron - recognize and combat diseases

Rhododendron - recognize and combat diseases

  • Sick because of defects / care mistakes
  • The pathogens
    • bacteria
    • mushrooms
    • virus

Rhododendrons are robust, when they look sick, they usually suffer from skin care deficiencies. Sometimes, deficiencies are also visible because they are sick, because then bacteria, fungi and viruses have an easy time. For sick rhododendrons, you should first start to eliminate all care mistakes. Meanwhile, you can immediately search for pathogens, which are then fought.

If the actually bursting with power rhododendron is sick, it is first to cause research: vote only the location and the supply is not or is really a disease to recognize "> Ill because of defects / care mistakes

No matter how unpretentious rhododendrons are, some minimum needs have to be met, otherwise the uncomplicated ornamental tree will be so affected by deficiency symptoms that it looks ill or becomes ill. You should therefore first deal with the care of the rhododendron; even if a rhododendron is already ill, supply shortages must be stopped before or with the disease treatment.

The site may not provide enough light, but for shady areas, partially shaded locations still need some light. Rhododendrons are not shady plants! But too much light, roasting constantly in the midday sun or growing on boiling pot roots weakens rhododendrons. The soil may be too basic, most rhododendrons prefer to grow in pH's between 4.5 and 5.5. It may also contain too few or too many nutrients, if you have no idea what direction it might take, a soil analysis is pending. If the diseased appearance of the rhododendron occurs after winter, it has probably suffered from freezing cold.

Rhododendron also needs light

When it's clear how best to provide the rhododendrons, research into the pathogen is on. You can stop most care mistakes immediately, only when transplanting you should wait for the identification of the pathogen, maybe it is already too late anyway and your rhododendron has to give way.

Deficiency symptoms can not only cause disease, but often result in rhododendrons having no strength enough to provide sufficient resistance to pests. These should be quickly and decisively reduced to as low a level as possible by the gentlest (mechanical) means, while at the same time the rhododendron is better supplied and strengthened by vigorous plant broths. This will prevent further weakening of the plant through chemicals while preventing the development of diseases.

The pathogens

If a deficiency condition / care mistake is turned off too late, it can weaken the plant in such a way that its organism is helplessly exposed to pathogens.

These pathogens infest rhododendrons:


Good news: Rhododendrons are so resistant to bacteria that since 2014 researchers are working to develop a new antibiotic from rhododendron antibacterial substances.


Fungi are everywhere in the air and are transported (even by pests) on rhododendrons, the most common types:

Fungal attack in rhododendrons
  • Phyllosticta species, causing irregular, brown-gray and dark outlined leaf spots
  • Ceroseptoria handelii, makes roundish to irregular dark brown leaf spots and gray fungus coating in moisture
  • Glomerella cingulata, usually extensive, irregular dark brown leaf spots and black spore beds, which can be seen with the magnifying glass
  • Botrytis, gray rot, leaf-tailing gray mold, spreading leaves turn brown and die


  • Generously cut away all diseased parts of the plant and make sure that the plant dries up quickly after watering
  • Do not dispose of cut-away shoots in the garden or use them for mulching, but remove them from the garden
  • Fungicides are permitted against some of the fungi, but they can only be used against precisely identified fungi
    • Fungicides may contain harmful substances, use is limited to extreme cases (ask local environmental office)

The fungi can also be confused with other leaf spot diseases, but the treatment is identical:

  • Pycnostysanus azalea, bud rot, causes flower buds to die off, "prickly" appearance, 1, 2 mm tall dark mushroom turf, which becomes visible under a magnifying glass
    • Remove all diseased shoots at the latest in autumn
Bud rot on rhododendron
  • Exobasidum japonicum, earlobe disease, causes deformities, leaf / flower parts thickened or spoon-shaped, white frosted in advanced stage
    • Remove all diseased shoots, if fungus is not curb, plant resistant rhododendron varieties
Rhododendron - wilting fungus
  • Verticillium alboatrum, wilting fungus, leaves pale or yellowish discolored, shoots withered, die off
  • Phythopthora, wilting fungus, leaves pale, pale or yellowish discolored, shoots withered, die off, in case of strong infestation plant enters
    • For the first few tracks, cut shoots liberally, remove and dispose of more diseased plants (do not compost), plant resistant varieties


There are viruses that infest rhododendrons, there is also mosaic discoloration caused by viral infection. Thankfully, this is very rare, because what does not exist is a cure for these viruses. If leaves are spotted yellow, piebald, slightly deformed, you can only fix and hope for all nutrient deficiencies; if the rhododendron can not prevail against the virus, unfortunately, it must be cleared.

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