We have several of these plants in our rental propert garden that are looking unhealthy- the leaves look like they're being chewed but I can see any critters on the plant. Not sure if pest or disease or if these plants have a limited lifespan as several have died in the last 6 months.
Disease or Pest Damaging Garden Plant
Certified GKH Gardening Expert
These yucca plants seem to be suffering from a fungal infection. This can usually be remedied by adding dolomitic lime and wettable sulfur to the area around each plant that is affected. This will repair the soil to a more suitable condition.