I have one word on this subject: diazinon. I had moved to a new
barn with my only horse at the time. The paddocks were overgrown and I
was mowing the paddock. I ran over a ground nest with the lawn mower and
they came flying out the back end of the mower by the hundreds and were
stinging my neck and arms (bees are the only thing in the world that I am not
allergic to). But the worst of it was when my mare came over to
investigate and they started stinging her. That really ticked me
off! I went right out and bought a quart of diazinon and poured it down
the nest hole. Not only did it kill the bees, it left a dead zone around
the hole about a meter in diameter. Great stuff!