Most pest control equipment is designed to apply a liquid or dust to plants. Good tools should apply it evenly, covering all the surfaces, even those shielded or hidden from view. They should be convenient to fill, use, and clean.
Because the materials being applied are often toxic to people or plants, it’s important to clean the equipment well after use. Remnants of herbicide in a sprayer used to spray aphids on roses can damage the rose plants. Some people keep a separate sprayer for herbicides to avoid this problem.
When selecting equipment, keep the scale of your job in mind. A simple trigger spray bottle is sufficient for a few house plants. A tank sprayer that holds one gallon is about right for a dozen rose bushes. If you will be killing weeds on a one-acre site, you probably want a 3-gallon backpack sprayer to avoid having to refill too often.