Rhododendron Diseases

Rhododendrons are one of the popular choices for landscaping, as they have spectacular and showy flowers. Rhododendron is a genus of flowering plants and it belongs to the family Ericaceae. Around 100 species of plants are included in this genus and most of these plants sport showy flowers. Azaleas are among the most popular rhododendrons that are commonly used for landscaping. However, these plants are prone to various diseases and most of them can be avoided with proper care and treatment.

What are the Different Rhododendron Diseases

One of the golden rules regarding rhododendron care is to take care of their requirements, right from planting, location, watering and pest control. Most of the diseases in these plants can be prevented to some extent with proper care.

Stem Dieback
One of the common rhododendron diseases is stem dieback, which is characterized by the death of the branches, in an otherwise healthy plant. This condition is caused by a fungus called Botryosphaeria dothidea. It has been observed that these dying branches have a reddish brown discoloration of the inner parts of the bark. If you notice any symptom of dying stems, then scrape the bark of such stems with a knife and check for reddish discoloration. This disease can be controlled by pruning. In other words, the infected (dying) branches have to be removed. Such pruned branches have to be disposed of in a distant location and the pruning tools have to be disinfected with bleach solution.

Leaf Gall
Leaf gall is commonly seen in azaleas, but, other rhododendron species are also prone to this springtime disease. In this case, the leaves, buds or stems develop swollen growths with distorted shapes. Sometimes, these growths may get covered with white spots too. This condition is caused by the fungus Exobasidium and it can be controlled by removing such swollen parts from the plant and disposing them by burning.

Oedema
This is also among the common rhododendron diseases. Usually, this condition develops during the later part of winter, especially, when the weather is cold, and the soil remains warm. This condition is characterized by the presence of water blisters on the leaves and other parts. It is caused by the over absorption of water by the roots and as the water pressure in the cells increase, blisters are formed on the leaves. In severe cases, blisters can be found on the flowers and other parts too. These blisters may also turn harder with time and resemble warts in appearance. This condition may eventually affect the growth of the plants and can be controlled by avoiding over watering and by spacing the plants, so that they get sufficient air circulation.

Chlorosis
Chlorosis is a disease characterized by yellowing of rhododendron leaves. This condition is caused by the non availability of micronutrients, that are necessary for the healthy growth of plants. These micronutrients include iron, manganese and zinc. So, it is always recommended not to plant rhododendrons in highly alkaline soil. As this yellowing can be caused by pollutants too, it is always better to keep these plants away from places, where they can be exposed to such chemicals. If you want to treat the condition, you have to test the soil, so as to get an idea about which nutrient is missing.

Powdery Mildew
This is one of the fungal rhododendron diseases and is characterized by white or gray blotches or coating on the leaves and other parts. You may also notice the affected leaves dropping off. In severe cases, the growth of the plant may get stunted. This disease is mostly found in humid climates and very rarely in cold weather. So, rhododendrons in the coastal areas are more prone to powdery mildew. This disease can be controlled by collecting and burning the affected leaves and spraying the plant with a fungicide.

There are various others, like leaf spots caused by fungus (can be controlled with fungicide), root and crown rot (can be prevented to some extent by planting in well drained soil). Even pests like aphids, bark, spider mites, scale, weevils and caterpillars can attack this plant. So, provide these plants with healthy growing conditions, so that most of these diseases can be prevented.