Q.Suddenly the plants are losing leaves and seem to be dying after 40 years in the same location — both green and purple oxalis.
What could cause a sudden disease in four oxalis plants located in the same spot for 40 years? They seem to be dying with spots on their leaves for not apparent reason. No change in care for over 40 years! Can you give me a specific address to send photos and I can do that

You can send photos here to this inbox. This will help me to pinpoint, exactly, what is going on here. My best guess without seeing it for myself would be a fungal infection. These are pretty resilient, and can fight it off with a little help. You can apply wettable sulfur to the area to kill off the fungal infection in the soil. Cut out any infected growth, and treat the soil, and you will start to see the new growth return to normal. What spots are on the old growth won't disappear, but you will be cutting those off anyway.