Q.starfish cactus
My plant seems to have this white mildew looking stuff on the stems? What is it?

Certified GKH Gardening Expert
Without seeing it, this sounds like powdery mildew. Neem oil will get rid of this, as will rosemary oil, or garlic extract. Mix one or more of these in water and spray the plant. You may spray the growing medium as well. Here is an article for more information on powdery mildew: https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm