Why is there black on the leaves?
Certified GKH Gardening Expert
That is a fungal issue. Sometimes it can die off, and be ok after a cold winter. If you would like to be sure that this infection is cured, then use wettable sulfur or copper salts. This will take care of the issue.
This link will take you to a collection of articles on making your own pesticides/fungicides/biocide: https://www.gardeningknowhow.com/special/organic/