It's white and powdery.
What is it?
Here is a link that might be useful: Bad White Stuff
Almost looks like powdery mildew, but I didn't think that it would grow on fleshy plants. In any case, spraying the affected plants with a mixture of 9 cups water to 1 cup milk should take care of your problem.
That's not powdery mildew (which tends to be greyish and without texture). That looks like mealybugs.
Here is a link that might be useful: