Question
I have had this peace plant for over 10 years and now I have been having problems with the leaves turning black What I'm I doing wrong.

Answer
Hi Karen,
Has the actual leaf turned brown or is there just a black coating on the leaves?
If it is a black coating then it is honey dew, a clear, thick, syrup like substance secreted by insects. Honey dew attracts black sooty mold that covers the leaves making them look black.
If the actual leaves are turning black Then it is probably root rot.
Remove the plant from its pot and check the roots. They should be light colored and firm. If they are dark and mushy then the plant has root rot.
The plant may not recover but there are things you can do to try to save the plant if the root rot has not affected too many roots.
Trim off affected roots. Make the cut about 1 inch into healthy root. Repot the plant in fresh soil. If possible repot in a pot 1 size smaller than the one it was in.
Water the plant only enough to keep it from wilting and keep it out of direct sunlight. When there is a good amount of new growth then return to the normal care appropriate for that plant.
I hope this helps. If you have any questions or need additional information please don't hesitate to ask.
Thanks
Tracy