An agricultural adjuvant or Foaming Agent is any substance added to a pesticide spray tank—or pre-formulated into a pesticide product—to improve the physical performance, application accuracy, or biological effectiveness of the active ingredient (such as an herbicide, insecticide, or fungicide).

While adjuvants do not control pests on their own, they help pesticides overcome real-world obstacles like waxy plant leaves, hard water, wind drift, and rapid evaporation.