Why does my yucca get black spot?
Certified GKH Gardening Expert
It sounds like your yucca has a fungus. Treat the plant with fungicide. I like to use neem oil myself as it is safe for people and pets and also will address any pest issues the plant may have. Here is more information on it: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm