Azalea gall and Camellia gall
Exobasidium japonicum and Exobasidium camelliae
Azalea gall causes fleshy growths on azaleas and other Rhododendron species. Camellia gall produces large cream-coloured swellings on camellias.
- Pale green or pinkish fleshy growths on azaleas and rhododendrons
- Large swellings on camellias, replacing leaves, turning creamy-white in colour
What are azalea gall and camellia gall?
Both azalea gall and camellia gall are fungal diseases, as opposed to most galls, which are caused by insects.
Azalea galls are fleshy, irregular shaped growths (galls) that appear on the surface of the leaves, or flowers, of azaleas and rhododendrons. Initially, they are pale green, or sometimes pinkish, turning white as the summer progresses due to the formation of a floury covering, or bloom, of fungal spores.
The galls vary in size from pea-sized, all the way up to 7.5cm (3in). The affected leaf or flower is more-or-less totally replaced by the gall. Several galls will appear on affected plants.
Camellia galls look quite alarming. They are creamy-white swellings that develop during the summer, replacing the leaves. Most commonly only one or two galls appear on each plant.
These galls can be up to 15cm (6in) in size and very variable in shape. At first, they have a firm texture, becoming spongier or softer as they age, and are green, turning creamy-white as the spores are produced.
What do they affect?
- Other Rhododendron species
What are azalea gall and camellia gall caused by?
Very little is known about the full lifecycle of either of these fungal diseases.
The spores of the azalea gall fungus and the camellia gall fungus are either air- or insect-borne, spreading the disease from infected to healthy plants. Symptoms of attack may take up to several months to appear after the initial infection by the fungus.
Both diseases are encouraged by damp and humid conditions.
How to control azalea gall and camellia gall
Try to keep plants growing as strongly as possible to help them fend off disease attacks. However, this may have little effect in controlling it.
Galls should be removed and destroyed as soon as they are seen. Repeat infections are less likely if this can be done before the bloom of spores develops on the gall.
Carefully pick off or prune out and dispose of affected leaves and stems as soon as the galls are seen to reduce or slow down its spread. This is highly unlikely to totally eradicate the disease. Try not to disturb the spores, or you will be spreading the disease further; enclose the gall in a plastic bag before removing it.
Similarly, carefully pick up or rake up affected fallen leaves – especially in autumn – to try and reduce carry-over through the winter.
No fungicides are available to gardeners for the control of this disease.
You may be able to help protect new growth and prevent the disease by spraying plants with a good garden fungicide.
Use plant protection products safely. Always read the label and product information before use. Plants in flower should not be sprayed due to possible danger to pollinating insects. Either spray early in the morning or late in the evening when pollinating insects are less likely to be active.
Nothing can be done to prevent azaleas, rhododendrons and camellias being affected by gall diseases. Aim to keep the foliage dry when watering, watering on to the soil rather than over the plant.