My forsythia bush leaves are turning almost black. What causes this, and what can I do?
Forsythia Turning Black
Certified GKH Gardening Expert
Are they soot-like? If so, this could be sooty mold. It is a byproduct of a pest infestation, likely aphids or scale. This article will help you with getting rid of it: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
Neem oil can help as well. In addition to treating whatever pests may be affecting the plant, it is also a good fungicide, which will help in the event that this is caused by some other type of fungus. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm