Hello, I've lived in Minnesota all my life and never recall seeing black leaves in autumn.
We were walking about in bovey mn and on the ground were hundreds, or thousands of full on black leaves. Not black spots. Black. Not dried up, crinkled leaves. They looked like freshly picked leaves. No tree had black leaves in them but amongst all the colorful other leaves laying on the ground were as many black leaves. I just don't recall ever seeing this and I am 62. Thanks for helping, Jan We were in Itasca county on the edge of the George Washington state forest.
Scott County Minnesota
The black fall leaves could be a result of the excessively wet spring and an abundance of fungal infections in our trees.
Anthracnose which affected many trees this summer can turn fall leaves black.