I have a willow tree that has black sticky stuff falling from it. everything under it has turned black. It is full of bees also. I see no bugs but the leaves are covered with black too. I have the same tree a few feet from it that doesnt have this problem. What can it be?
It's probably aphids, a sucking insect pest that feeds on the sap and excretes a sticky "honeydew". Black "sooty mold" grows on the honeydew covered surfaces. The sooty mold is not harmful but the aphids can weaken the tree and cause branch die-back.
I suspect that the "bees" are not honey bees this time of year because a willow will not be in flower to attract pollinators. It is likely to be wasps/hornets feeding on the honeydew and maybe on the insect pest.
Without a photo or description of the size of the tree and growing conditions, it's hard to go any further with giving advise on control. A systemic insecticide would be best, to avoid having to spray a large tree with a contact insecticide.
The fastest acting and most effective systemic insecticides are available to professional applicators, like a tree service with a plant health care operation, or a landscape pest control company.