Rhododendron bud blast
Pycnostysanus azaleae
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How to spot it
Rhododendron bud blast is caused by the fungus Pycnostysanus azaleae and attacks above all rhododendron and azalea. Affected flower buds turn brown to greyish black, dry up and no longer open in spring; they often stay hanging on the shrub for months or into the next year. In autumn and winter you recognise the fungus by fine, bristle like black fruiting bodies growing out of the bud scales. The fungus frequently uses the feeding punctures of the rhododendron leafhopper as its point of entry, which is why bud blast often occurs together with leafhopper infestation.
Prevention
Pick off dried, brown buds consistently and dispose of them with the household waste, not on the compost, so that the fungus does not spread further. Provide an airy position with enough space between the shrubs and thin dense plantings regularly, so that flowers and buds dry off quickly after rain. Since the rhododendron leafhopper is regarded as the door opener, it helps to keep an eye on its infestation and to cut affected shoot tips back early. For new plantings use, where possible, tough, healthy stock from a trustworthy source and avoid permanently damp, shady spots without air movement.
Affected plants
These plants in our database are especially susceptible.
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