Any cure for white mould/powdery mildew?

[Primrose]

I have an attractive acanthus plant which unfortunately for the second year has had its leaves badly attacked by a white mildew of some kind

Is there any spray I can use to cure this? . We can cut off and destroy the worse affected leaves but wonder if the plant's longterm life is now doomed?

[oldherbaceous]

Dear Primrose, don’t think there are any sprays that the general public can buy these days, that actually work.
Maybe a good watering and mulch might help with the problem….