Underground Wasp Pesticides

Nothing can ruin a barbecue or outdoor gathering quite like the threat of yellowjackets -- commonly encountered, aggressive, ground-dwelling wasps -- or the sight of buzzing wasps, but it's not always as dangerous as it's made out to be. If you have an underground nest of social wasps, a few considerations can go a long way toward keeping your family safe while controlling the problem at hand. Many wasps and bees are beneficial, however, so control should be a last resort.

Several different pesticides are commercially available with several different active ingredients. Some of these active ingredients include carbaryl, chlorpyrifos, acephate, diazinon, permethrin and esfenvalerate. Carbaryl is among the most commonly found insecticides in stores, although a quick browse of your favorite hardware store's shelves may display several of these. Most, including carbaryl, chlorpyrifos and acephate, work by attacking the wasps' nervous systems.

If you've looked for a wasp insecticide at any number of retailers, chances are you've come across cans labelled "Wasp and Hornet Spray" or something similar. While these products may knock down or freeze wasps and hornets you catch flying about or those who have built aerial nests, spraying these products into an underground nest will likely send underground workers into a defensive frenzy which means several -- if not dozens of -- stings for you. Waiting until nightfall and shooting steady streams into the nest may work, however, but there is still considerable risk as the jet streams are narrow and will allow defensive workers to come out of the nest. For underground wasps, choose a carbaryl dust or other dust insecticide labelled for wasps.

Wait until nightfall when all the yellowjackets are in their nest and use a red-light flashlight to find the opening, as wasps cannot easily see red light. Sprinkle the dust around the opening and down into the entrance. The workers will crawl through it on their way out and into the nest, spreading it slowly. You may need a couple of applications spread a few days apart. Another option is to use a hand duster or power duster -- you can pick this up at a hardware store or purchase online -- with a long tube to stick down the entrance cavity closer to the nest. Never use a power duster that has contained insecticides for any other application.

Nearly all social wasps die when the weather turns cold, except for mated females who will be queens of their own colonies the following spring. If at all possible, avoid the nest area through the summer and block off the nest entrance in autumn so new queens don't colonize it the following year. Wasps are also less active when the temperatures drop in autumn; wait until a cool night to apply. On the other hand, wasp nests are much smaller early in the spring as the new queens begin colonizing; if you catch the nest early enough in the season, it may be simpler to control. Wear long, protective coating to protect from potential stings.