The backpack mist blower has become a popular application method for mosquito control services. While it works well overall, keep in mind most units are gravity-fed. That means anything poured into the tank can enter the chemical hose before it is agitated.
To minimize risks with contact or with uneven dilution, dilute the insecticide in a separate container before adding it to the backpack mist blower tank. If that’s not possible, fill the tank halfway full of water before adding the insecticide. Avoid pouring over the gravity-fed chemical tube. Finally, be sure to inspect the chemical tube for the presence of undiluted insecticide before use.