The stems on my holly bushes are turning black. I can't seem to find out the cause or the solution to the problem.
Certified GKH Gardening Expert
It sounds like you have sooty mold. This article should help: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm This is a fungus caused by the pests. I would treat the plant with neem oil. It is effective against the pests responsible as well as the sooty mold. Here is more information that may help you: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm