Wasps are beneficial insects, but can represent a potential hazard anywhere near the home. Hundreds of people die from allergic reactions to the venom of wasps, bees and hornets each year. The risk of being stung increases when wasps build nests near a house, especially when wasps build a nest on a wood deck that people frequently use. Paper wasps chew wood and scraps of paper or cardboard to construct a nest, which they attach to the underside of the deck, deck railing, steps or under the house overhang. By summer's end, each nest can contain hundreds of wasps.
Purchase supplies. Go to the store and select an aerosol insecticide that states on the label it is for wasps. Insecticides with both long-acting and short-acting ingredients, along with the persistent chemical permethrin, work well to control wasps, according to Colorado State University Extension.
Locate the wasp nest. Look for an umbrella-shaped structure hanging down. Check carefully because there might be more than one nest. Since wasps are active during the day, you might more readily locate nests by observing wasps flying back to their nest, or, to lessen the risk of being stung, look for nests late in the evening or in the cool early morning when wasps are less active.
Don protective clothing before you spray. Although you can spray insecticide on wasp nests without it, wearing protective eyewear, gloves and outer clothing helps to protect you in case the wind changes and blows insecticide spray back toward you. In addition, those items plus a veil over your face protect against potential stings.
Spray insecticide directly on the nests following the instructions on the label of the product you are using. After dark is the safest time to spray, followed by the early morning hour of cool temperatures. However, if you must spray during the day, do not stand directly below the nest because most sprays cause wasps to drop immediately, increasing your chance of being stung if a wasp falls on you.
Wait at least one day after spraying to make sure no live wasps remain. If so, spray it again with insecticide. The day after no wasps remain alive in the nest, knock it down or scrape it off the deck or the overhang to make sure the empty nest does not attract scavenging insects, carpet beetles or ants to colonize the nest and cause other problems.