Very interesting that a single apple could divert all the wasps from your campsite. I will try an apple next summer for my wasp problem.
Meanwhile, I've also found that a little peppermint oil mixed with water (maybe 1 tsp oil to a pint of water) and put in a spray bottle is pretty effective.
Spray all the eaves of your house and other structures and anywhere else you expect wasps to nest. Shake the bottle frequently.
Not exactly a non-violent solution, but definitely better than toxic wasp spray. And it's preventative, too, rather than curative.