Types of Pesticides
Pesticides can be grouped in a number of ways, including by their formulation. Common pesticide formulations include but are not limited to:
- Emulsifiable concentrates
- Wettable powders
- Soluble powders
- Ready to use
Many pesticides come in both ready-to-use and concentrated forms, so homeowners may need to weigh their options. Ready-to-use products also tend to be easier and safer for homeowners to use, since they don’t require any calculations or mixing. But in the long run, they tend to have a higher cost per application than concentrated products do. If a concentrate is chosen, homeowners should mix only enough material to do the job. It’s important to keep in mind that the formulation of a pesticide also dictates how it can be applied.
Pesticides can also be grouped according to their activity, though many pesticides can work in more than one way. Perhaps the broadest groups are selective and non-selective pesticides. A selective pesticide only kills certain kinds of plants or animals. For example, herbicides with the active ingredient 2, 4-D are used to control broadleaf weeds in lawns but are not harmful to most turfgrasses. On the other hand, a non-selective pesticide will kill most plants or animals that they contact.
A systemic pesticide, also known as a translocated pesticide, is absorbed and circulates throughout the target pest after entering through an initial uptake site (the mouth in animals or the roots or leaves in plants). A contact pesticide will kill pests on contact, while a stomach poison will be lethal after a pest swallows it.
A fumigant is a pesticide that forms gases that are toxic to plants, animals, and microorganisms.
A few other terms are often used when referring the herbicides. A preemergence herbicide is used before weed seeds sprout or emerge from the soil. Thus, timing is critical. Preemergence herbicides must be applied within a specific window based on the life cycle of the plants you’re trying to target.
A postemergence herbicide is used after weeds have emerged from the soil. Gardeners often spot-treat weeds in the lawn with postemergence herbicides. However, if more than half of a lawn is weeds, the better option is often to apply a non-selective herbicide to the entire lawn area and replace it with new sod or plugs.
Pesticides can also be grouped by chemical family, e.g. by their active ingredients. Some common pesticide families include organophosphates, pyrethrins and pyrethroids, carbamates, organochlorines, phenoxy herbicides, and anticoagulant rodenticides.