Troubleshooting
Canna 'Roi Humbert' problems — and how to fix them
Canna 'Roi Humbert' (Canna 'Roi Humbert') 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.
Canna leaf roller
Caterpillars roll and chew young leaves. Inspect regularly and remove by hand; use Bt (Bacillus thuringiensis) for heavier infestations.
Rust (Puccinia thaliae)
Orange-brown pustules on leaf undersides in warm, humid weather. Remove affected leaves promptly and improve air circulation.
Rhizome rot
Caused by waterlogged soil, especially over winter. Ensure good drainage and store lifted rhizomes in dry, frost-free conditions.
Slugs and snails
Feed on emerging shoots in spring. Use iron phosphate pellets or copper barriers; check under mulch regularly.
Viruses (Bean yellow mosaic)
Causes streaked, mottled foliage. Transmitted by aphids — control aphids early and remove and destroy affected plants.
Prevent canna 'roi humbert' problems before they start
Most canna 'roi humbert' issues are care-mismatch, not bad luck. Dial in the basics:
Canna 'Roi Humbert' problems — FAQ
Why is my canna 'roi humbert' canna leaf roller?
Caterpillars roll and chew young leaves. Inspect regularly and remove by hand; use Bt (Bacillus thuringiensis) for heavier infestations.
Why is my canna 'roi humbert' rust (puccinia thaliae)?
Orange-brown pustules on leaf undersides in warm, humid weather. Remove affected leaves promptly and improve air circulation.
Why is my canna 'roi humbert' rhizome rot?
Caused by waterlogged soil, especially over winter. Ensure good drainage and store lifted rhizomes in dry, frost-free conditions.
Why is my canna 'roi humbert' slugs and snails?
Feed on emerging shoots in spring. Use iron phosphate pellets or copper barriers; check under mulch regularly.
Why is my canna 'roi humbert' viruses (bean yellow mosaic)?
Causes streaked, mottled foliage. Transmitted by aphids — control aphids early and remove and destroy affected plants.