Pests and Diseases Viewer

Rhododendron Bud Blast


Rhododendron Bud Blast

Usually appear in

Spring to Autumn

Back to Pests and Diseases

Caused By:-     The fungus Pycnostysanus azaleae


Rhododendron bud Blast is a fungal disease of Rhododendrons and Azaleas caused by the fungus Pycnostysanus azaleae, which affects the tight dormant flower buds. This fungus is associated with infestations of the Rhododendron Leaf Hopper which acts as a vector or carrier of the fungus.
Later as the fungus grows it produces black, bristle-like fruiting spores on the surface of the bud, by this time the damage is done and the bud will not open and cannot be treated. The fungus can remain active in the dead bud for several years, so it is essential to remove infected buds as soon as they are seen.
The disease if more noticeable in the spring, when buds will be dark brown and covered in the small black hair-like growths of the fungus disease.
The affected Rhododendron or Azalea buds will be firm to the touch, unlike those of healthy buds or frost damage buds. Any insect visiting the infected bud is then a potential carrier for the fungus to other healthy buds.
The fungus spores are thought to be carried by the Rhododendron Leaf Hopper, which lays it's eggs in the Rhododendron and Azalea buds in late summer. This egg laying damage, to the bud, is probably the point where the spores to enter the buds. Rhododendron Leaf Hoppers are active during late summer and early autumn.
Picture by Cheryl Moorehead, individual,


Treating Rhododendron Bud Blast is best done by a two pronged attack. Firstly, any brown or otherwise discoloured buds should be removed as a matter of routine and burned.
Secondly, keep an eye open for the pale green leaf hoppers or other aphids or insects that can be a vector for the disease.
Then spray with an insecticide and a fungicide.
These vectors will appear again in following years and it is important to check with neighbours, as their Rhododendrons are most likely affected as well and will harbour the fungus and need treatment.

Back to top