Though helpful in eliminating other insect pests, wasps can be a painful nuisance around the home. To effectively kill a troublesome wasp population around your house, you'll have to locate the source nests. The ultimate goal here is not just to kill the worker wasps in the nests, but to destroy the nests themselves with the queen wasp inside, since it's the queen that builds new nests and initiates new colonies every spring.
Locate the wasp nests. Queen wasps frequently build their nests under roof eaves and in wall cavities.
Mix equal parts lemon oil and water, and pour the mixture into a pump garden sprayer or water pistol that can spray targets from at least 10 feet away. Lemon oil kills wasps on contact, without the need for toxic chemicals.
Go back to the nests at nighttime, which is when wasps return to their nest, and thoroughly douse the nests. Prepare to run if the wasps inside the nest have been roused.
Return to the nests during the day to inspect for further activity. One or two more nighttime lemon oil and water sprays will probably be necessary.
Remove the nests at night, when any surviving wasps will be at their least aggressive. Burn the wasp nests in a wood stove, outdoor campfire, or backyard burn barrel.
When spraying and removing wasp nests, be sure to have your body completely covered, to protect against wasps attacks. This means wearing a heavy, long-sleeve top, long trousers, outdoor gloves, and a hat.