Many questions have come into the office in the last week about Yellow Jacket wasps. Bottom line is they are at their most active this time of year and populations are high so control is difficult.
A few thoughts on control:
1) Wasp sprays may be purchased over the counter at most hardware stores. Wait until the early morning or late evening before spraying or removing a nest since that is the time of day they are least active and you are least likely to get stung. For those of us that do not like to get up close, a long distance spray option is often available. Dusts, such as Sevin, may also be used for inground nests.
2) If you are exhausting all options that you are aware of or are uncomfortable doing yourself, then consider calling a Licensed Pesticide Applicator or Trained Service Person (i.e., pest exterminator).
For more discussion, see the fact sheet from OSU on yellow jackets available on Ohioline, http://ohioline.osu.edu/hyg-fact/2000/pdf/2075.pdf