White spots on acanthus leaves
What are the white spots and what do I need to do about them?
Certified GKH Gardening Expert
That sounds like powdery mildew. You can remedy this with neem oil, rosemary oil, garlic oil, and/or lavender oil. Here is an article for more information: https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm