You sure it was a wasp? I think a hornet's sting is more intense.
Dry year.. August and September will be worse.
If you can't beat the wasps, and there's nothing for them to eat..... put out a plate of honey infused with 190 proof whiskey. Keep 'em drunk. A drunk wasp is a happy wasp.
Or put a few wasp traps around the yard and garage.
http://tipnut.com/wasp-trap/