Troubleshooting
Canna 'Black Knight' problems — and how to fix them
Canna 'Black Knight' (Canna 'Black Knight') 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
Larvae roll leaves and feed within, leaving untidy brown edges. Remove by hand or apply Bt to young caterpillars.
Rust
Orange pustules appear on leaf undersides in humid conditions. Remove affected foliage and avoid overhead watering.
Botrytis (grey mould)
Can attack stored rhizomes in damp conditions. Allow cut surfaces to dry for 24 hours before storage and keep stored material in barely moist vermiculite.
Virus (mosaic)
Mottled or streaked leaves signal viral infection carried by aphids. Remove and destroy infected plants to prevent spread.
Slugs
Particularly damaging to emerging shoots. Use iron phosphate bait in spring as shoots push through the soil.
Prevent canna 'black knight' problems before they start
Most canna 'black knight' issues are care-mismatch, not bad luck. Dial in the basics:
Canna 'Black Knight' problems — FAQ
Why is my canna 'black knight' canna leaf roller?
Larvae roll leaves and feed within, leaving untidy brown edges. Remove by hand or apply Bt to young caterpillars.
Why is my canna 'black knight' rust?
Orange pustules appear on leaf undersides in humid conditions. Remove affected foliage and avoid overhead watering.
Why is my canna 'black knight' botrytis (grey mould)?
Can attack stored rhizomes in damp conditions. Allow cut surfaces to dry for 24 hours before storage and keep stored material in barely moist vermiculite.
Why is my canna 'black knight' virus (mosaic)?
Mottled or streaked leaves signal viral infection carried by aphids. Remove and destroy infected plants to prevent spread.
Why is my canna 'black knight' slugs?
Particularly damaging to emerging shoots. Use iron phosphate bait in spring as shoots push through the soil.