Natural Wasp Control

Prevention (http://eartheasy.com/live_natwasp_control.htm)

Remove food sources. In the spring and early summer, wasps are attracted to protein foods. Any food left outdoors, such as pet food, picnic scraps, open garbage containers or uncovered compost piles should be removed or covered. Wasps imprint food sources, and will continue to search an area for some time after the food has been removed.
In late summer and early fall, the wasp food preference turns to the sweet. Their behavior is also more aggressive. Open cans of pop, fruit juice, fallen apples beneath fruit trees and other sweet food sources will attract wasps. Be sure to cover drinks and open food containers, keep a lid on the compost and avoid walking barefoot near fruit trees. Pick up and dispose of any fallen fruit rotting on the ground.
Avoid swatting. Swatting and squashing wasps is counterproductive. When a wasp is squashed, a chemical (pheromone) is released which attracts and incites other nearby wasps. It's best to walk away from a hovering wasp.
Avoid wearing bright colours or floral patterns.If you look like a big flower, you may be attracting the curious wasp looking for nectar.
Minimize use of perfumes and other strong scents. In the later part of the summer, wasps are attracted to sweet smells.

Traps

Setting out traps in the early spring, when only a few wasps may be evident, can be most effective. This is because these early season wasps are usually queens, and it's estimated that each trapped queen represents several thousand worker wasps in the late summer. You can buy wasp traps or make your own.

A cheap and effective wasp trap. (http://www.pestcontrolcanada.com/wasps.htm) 

This simple homemade trap will not eliminate all the wasps that leave nests to forage, but if a number of them are placed in the right locations, they can effectively reduce the population to a tolerable level and attract these pests away from your area of activity.

1. Cut the top off a 2 litre plastic pop bottle.  Make the cut just at the top of the straight sides.

2. Invert the cut off top into the bottom portion and staple in place.

3. Pour a sweet smelling liquid into the funnel top you have made. About 2 inches of liquid in the bottom of the trap is enough. Carbonated pop (cream soda) seems to work well but try something different in each one to determine what your wasps prefer. 

4. Place your traps in a wide circle 30 to 50 feet away from the area you want to be "wasp free". Try to place some of them in the flight path. 

5. If you smack a few with a fly swatter, put them in the top of the trap.  The dead ones give off an
   alarm scent that will attract  others. 

Wasps can travel up to one mile in search of food.

Wasps can sting more than once.  Unlike bees, they do not loose their stinger when they attack. 

Nests are often located in holes in the ground.  Be careful where you step.  Wearing shorts creates a natural target if you step on a nest.  

People who get stung often do not build up an immunity.  The reaction often gets more severe after a number of stings over a period of time.