Ants farming aphids on the ends of your cherry branches. I’m dealing with it too. Can try neem oil but it’s doing nothing for me. I try to avoid serious pesticides but I had some permithrin laying around so sprayed the leaves to take care of the ants and aphids. I have dogs so have to be very careful. Also don’t want to harm bees.
You can try a systemic aphid killer. Start it early next year to prevent this.