Troubleshooting
Dahlia 'Contraste' problems — and how to fix them
Dahlia 'Contraste' (Dahlia 'Contraste') 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.
Powdery mildew
Particularly problematic on large-flowered varieties in late season; maintain airflow and apply preventive fungicide sprays from midsummer.
Aphids
Especially black bean aphids on tender growth; spray with insecticidal soap or introduce biological controls such as lacewing larvae.
Stem canker (Botrytis)
Dark lesions at stem base in wet conditions; remove affected stems at soil level and improve drainage.
Earwigs
Nest in the reflexed petals of cactus types; set cardboard traps overnight and remove pests each morning.
Tuber rot in storage
Allow tubers to cure for 10-14 days after lifting before packing in slightly damp coir; inspect monthly over winter and remove any rotting sections promptly.
Prevent dahlia 'contraste' problems before they start
Most dahlia 'contraste' issues are care-mismatch, not bad luck. Dial in the basics:
Dahlia 'Contraste' problems — FAQ
Why is my dahlia 'contraste' powdery mildew?
Particularly problematic on large-flowered varieties in late season; maintain airflow and apply preventive fungicide sprays from midsummer.
Why is my dahlia 'contraste' aphids?
Especially black bean aphids on tender growth; spray with insecticidal soap or introduce biological controls such as lacewing larvae.
Why is my dahlia 'contraste' stem canker (botrytis)?
Dark lesions at stem base in wet conditions; remove affected stems at soil level and improve drainage.
Why is my dahlia 'contraste' earwigs?
Nest in the reflexed petals of cactus types; set cardboard traps overnight and remove pests each morning.
Why is my dahlia 'contraste' tuber rot in storage?
Allow tubers to cure for 10-14 days after lifting before packing in slightly damp coir; inspect monthly over winter and remove any rotting sections promptly.