At my work site we have a large number of yuccas. They are starting to die. The first thing I notice is that the plant gets a black spot on the leaves and then more and more appear. The plant’s leaves start browning, and eventually the whole plant dies. I do not water or feed our yuccas. This black spot on the leaves, is it the same as black spot on tomato plants? Can you please assist?
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