Many wasps, including the infamous yellow jacket, build nests underground. A mature nest can contain hundreds of these dangerous and pesky insects, and wasps will defend their nest aggressively when threatened. Because of the danger involved, your best bet is to hire a professional exterminator to remove a large nest, though this can be costly. There are a couple of reliable methods you can try if you're willing to run the risk of getting stung. These methods will kill any variety of wasps, though a large mature nest may be more difficult to tackle.
Determine what kind of wasp inhabits the nest. If they are 5 cm (2 inches) or longer, they are probably cicada killers and pose no danger to humans. If they are less than 2.5 cm (1 inch) with black and yellow stripes, they are yellow jackets. Proceed with absolute caution if you discover a yellow jacket nest.
Approach the wasp nest when they are the least active. Wait until dusk or early morning before the sun comes up. Locate the entrance hole and any other escape routes. When doing this, use a red lens flashlight because bees and wasps cannot see red and will therefore not be attracted to the light, allowing you to see what your doing and stay safe.
Pour about 1 litre (1 quart) of liquid insecticide down the entrance hole to saturate the nest. Insecticides of this sort are usually pyrethoid compounds. You can also use about a half a cup of Sevin 5% garden dust. Make sure to apply whatever you use to the main entrance and any other holes leading to the nest.
Spray any remaining wasps with conventional wasp spray. You can shoot from a safe distance, 3 to 6 m (10 to 20 feet) away. Saturate the entrance, the inside of the nest, and any ventilation holes with the wasp spray.
Seal the hole with a large rock to ensure the wasps do not return to that nest. You can also use a plastic or metal container to contain the wasps.
Cover the hole with a screen before you attempt spraying to make an additional barrier between you and the wasps. Don't wear bright coloured clothing or scented cosmetics, as this attracts wasps. Drowning the nest with water can also be quite effective.
Do not attempt to remove a large yellow jacket nest by yourself, especially if you are allergic.