Fill a plastic spray bottle with vegetable oil.
Spritz a puff of the vegetable oil onto the surface of standing water. Afterward, you’ll see an oil slick on the water.
Squirt another puff of vegetable oil onto the water if the first amount you sprayed wasn't enough to cover the water's surface completely with a light oil slick. The mosquito larvae will quickly drown and egg rafts will sink before they can hatch. The oil will evaporate within one or two sunny days.
Repeat the vegetable oil treatment once weekly.