Wasp and hornet spray, WD-40 or a hot and soapy solution kill wasps. Typically, the best product to kill wasps is dependent on the location of the wasps. If there is a large nest or the wasps are very aggressive, it is advisable to call professional exterminators.
If possible, it is best to attempt killing wasps in the spring before the wasp queen has established her colony. Spraying wasp and hornet spray into the entrance of the nest is effective for most wasp infestations. Saturating paper wasp nests with the product at night when the wasps are less active makes killing them easier.
Applying WD-40 can also be useful in killing wasps, but the wasp location may make it impractical. This may include when nests are located in plants or shrubs. An effective option for an aerial nest is to cover and seal it with a trash bag and later freezing or leaving the bag in the sun to kill the wasps inside the bag.
Pouring a hot and soapy solution into the entrance of the nest and then sealing the nest with dirt or a boulder is s solution for dealing with wasps located in the ground. Because such nests typically have two entrances, it is important to locate them both before starting. A less environmentally friendly option is to pour paint into these same ground nests to kill the wasps.