Yellowjackets at launch declared war on us Sunday, with multiple surprise attacks.
This morning I went to launch early with two cans of wasp spray. I found two suspicious looking holes. The one nearer the stairs I don't think was actually a nest, but it looked very much like the hole near launch that had all the wasps around it. I never actually saw a wasp go in it, though. I loaded it up with the wasp spray, which made a foamy goop. Then I went out to the parking lot, having read that wasps will leave the nest and attack if they detect poison being introduced to their lair. I did that three times. By the third time, there were no more wasps hanging around the hole. There weren't any bodies, though..
There still weren't any live wasps or bodies in the afternoon, so I shoved a rock down the holes and covered them up with dirt. I left the flags near the former holes in case you still want to avoid them, but I think I won.