To kill a large plane tree is it sufficient to drill a 1" downward
sloping hole in its truck and fill this with copper sulfate?

Will the copper sulfate therefore be circulated thought the tree?

Well in some country can be very expensive if you are caught by police! In switzerland photos are taken by helicopter so you cannot cut a tree in your property without previous demand to the Forest /territory management authority, it cost normally abozût 20 -30 k US$
BUT according the species and size of the tree.. you can drill a hole and fill it with cheese .. will rotten and will kill the tree.
you can put mercury also inside ( but poisoning environment at the same time..
Hoping that thunder will strike it so will burn

a undetectable method is .. if the tree sleeps in the winter to warm up the soil enough to impeach sleeping .. when frost will come will kill the tree.. sometimes it takes 2 years .. if is a large tree /huge, will be impossible …