What are the white spots and what do I need to do about them?
White Spots on Acanthus Leaves
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