Troubleshooting
Rosebay Rhododendron problems — and how to fix them
Rosebay Rhododendron (Rhododendron maximum) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Chlorosis
Iron deficiency from alkaline soil causes interveinal yellowing. Lower soil pH with sulfur or ericaceous compost and apply chelated iron.
Root rot (Phytophthora cinnamomi)
Water-moulds thrive in poorly drained situations. Plant in raised beds if drainage is suspect and avoid irrigation at the crown.
Rhododendron gall midge
Tiny larvae cause leaf margins to roll inward in spring. Remove and destroy affected leaves early; pyrethrin sprays help with severe infestations.
Borer damage
Rhododendron borer larvae tunnel into stems causing dieback. Prune out affected wood below entry holes and destroy it.
Powdery mildew
White fungal patches on leaves in late summer; improve air circulation and avoid wetting foliage when watering.
Prevent rosebay rhododendron problems before they start
Most rosebay rhododendron issues are care-mismatch, not bad luck. Dial in the basics:
Rosebay Rhododendron problems — FAQ
Why is my rosebay rhododendron chlorosis?
Iron deficiency from alkaline soil causes interveinal yellowing. Lower soil pH with sulfur or ericaceous compost and apply chelated iron.
Why is my rosebay rhododendron root rot (phytophthora cinnamomi)?
Water-moulds thrive in poorly drained situations. Plant in raised beds if drainage is suspect and avoid irrigation at the crown.
Why is my rosebay rhododendron rhododendron gall midge?
Tiny larvae cause leaf margins to roll inward in spring. Remove and destroy affected leaves early; pyrethrin sprays help with severe infestations.
Why is my rosebay rhododendron borer damage?
Rhododendron borer larvae tunnel into stems causing dieback. Prune out affected wood below entry holes and destroy it.
Why is my rosebay rhododendron powdery mildew?
White fungal patches on leaves in late summer; improve air circulation and avoid wetting foliage when watering.