Major, have ya tried those traps you can buy?
Duggan, if I may put in my 2 cents' worth: I lived in Ester, Alaska for 40 years and had to deal with yellow jackets every summer. The interior has weather very favorable to hornets and yellowjackets, and some years we had huge numbers of nests.
We had a number of methods to trap and kill them.
Just as a reference, hornets are black, but not usually aggressive unless they feel threatened. Yellow jackets have yellow and black striped, pointy abdomens and these creatures are voracious hunters and mean as hell.
The purchased traps work well if you bait them with some kind of meat or seafood. In a pinch, this homemade version works very well:
You need a shallow pan or plant saucer, some dish soap, and some kind of meat, cooked or raw.
Fill the pan with water and drop liguid dish soap on the water till you have a soapy film. Place about a tablespoon of the meat in the middle of the pan. Some of the meat must stick above the water to give off an odor.
The wasps will swarm all over that piece of meat, and many of them will get soapy water in their breathing holes along their abdomens, fall into the water, and drown/suffocate. The next day the pan will be FULL of dead wasps. Just empty and reset the trap.
Another method is to wait till dusk, when the wasps return to the nest. Then spray with that petroleum-based spray in the yellow can. Soak the nest. When most of the wasps are dead, you can knock the nest down,place it in a plastic bag, then incinerate it. You have to kill the queen to kill the nest, and she is deep inside, near the top.
For ground nests, pour gasoline in their holes. But don't light it, as you'll start a ground fire, and those are very difficult to extinguish, once they get going underground.
A preventative measure is to kill every young wasp you see, early in Spring, as these are the new queens looking for a place to start a nest. These early queens often find their way into the house and can be seen flying around a window, searching for a crack in the wall to start the nest. At this stage of life they look all shiny and new, and don't have the swollen abdomen full of eggs yet. (I wont get into their life cycle here).
Remember, each young queen you kill is a thousand wasps that never get born.
Works great! Ffffooot, fffooot, fffooot - you can hear 'em smack the bend in the hose as they get sucked through. 
between the traps and the CO2 bombs I'll be surprised if they survive 
to ponder the wonders of growing.
