Rhododendron Diseases

If you are trying to maintain a beautiful yard with stunning flowers, the last thing you want to deal with is rhododendron diseases. With rhododendrons, like most flowers, one of the rules of thumb to go by is that many problems can be avoided by placing your plants in the best possible location. If you've tried to do that but still are having problems with rhododendron diseases, take heart. Here are some basic facts about these maladies.


One of the rhododendron diseases that is sure to break your heart is dieback. A plant with dieback will begin to have branches dying even though it seems healthy otherwise. If you scrape the branches under the bark with a knife, you'll find a red-brown color.

Dieback is caused by a fungus. Certain varieties of rhododendron are less susceptible to dieback. To treat, remove and dispose of all diseased or dead plant parts. Use a bleach solution to clean your tools afterward.

Leaf Spots

Leaf spots are rhododendron diseases that cause mainly cosmetic damage to the plants, although a severe case can cause the leaves to fall prematurely. Take care not to get the leaves wet when watering the plant. You can spray the plant with a fungicide, but don't do this when the humidity is high because it can damage the leaves.

Leaf Gall

Leaf gall is characterized by swollen, misshapen places forming on the buds, leaves, or stems in April or May. Like many other rhododendron diseases, the growths are caused by fungus. Leaf gall can be controlled by picking them off the galls and destroying them.


Micronutrient chlorosis refers to a condition in which the plants do not receive enough of certain minerals or other micronutrients. Yellowing of the leaves is characteristic of this member of the rhododendron diseases. It can be caused by pollutants, such as those found in building supplies. A preventive method is to plant your rhododendrons away from driveways and areas where you are storing building supplies.

Rhododendron Oedema

One of the rhododendron diseases that sounds like a human disease is oedema. This term refers to the condition of retaining too much water in the cells, which causes blister-looking areas on leaves and elsewhere.

Plants get oedema when the weather is cool and damp but the ground is warm. The plant absorbs more water under these conditions than can be given off by the leaves. Oedema can be avoided by not over watering and by planting them so that they have enough space for air to circulate around the leaves.

Petal Blight

Petal blight is a condition in which you may see spots on the petals. The spots get larger and become moist, causing the flowers to rot. Again, this is one of the rhododendron diseases caused by a fungus, and like the other fungal diseases, it can spread from flower to flower.

Treatment is to pick off and destroy any flowers that show signs of the disease. Water the plants from below and make sure you are using a mulch that is free of contamination. Be sure to destroy the diseased blooms because this is a fungus that can live in the soil all winter to contaminate the plants again next year.

Root and Crown Rot

Finally, one of the most common of the rhododendron diseases is root and crown rot. This problem often presents itself as a wilted rhododendron with leaves curling inward. Prevention includes making sure the ground is well drained and not planting the rhododendron too deeply. Look for healthy plants in the nursery and do a little research to find varieties that are resistant to the disease. Don't remove a plant with root rot and then plant a new healthy one in the same hole, either, because the disease can spread to the new plant.

See Also:

Epsom Salts on Rhododendrons