Becky, if misery loves company, we can help each other. I have the same situation with my big 7ft. Charles Grimaldi plant that is in my pool cage. It's been in the same pot for @ 4 years and I noticed it declining about a month ago. I just assumed it's an old plant and has developed some sort of trunk rot. Luckily for me, there are two other strong stems growing from the base of this one, so when the main trunk fails I have new growth to replace it.
Once the weather is cooler I'm going to tackle re-potting it with fresh soil to get rid of whatever fungi are in the soil now. We had such a hot, dry July then wetter August and wetter still this month until this last week has just been a deluge every day. I have all sorts of fungi sprouting, attacking my orchids, growing on pots and in the garden. The orchids I am treating with both a systemic and a spray fungicide, but the brugs grow back so fast, I really don't feel the need to save them.
If I did, my "go to" is the Bayer Advanced 3-in-1 which is fungicide, insecticide and miticide all in one. You mix it up as a douse and water the plant with it. Physan is the spray fungicide I use to clean the pool cage and pavers of fungus and algae. I hate using chemicals at all but this time of year it's necessary.
