Mode of action is the biochemical target a pesticide hits, such as a nerve receptor, a growth process or energy production. The Insecticide Resistance Action Committee (IRAC) sorts insecticides and miticides into numbered groups by mode of action, and recommends that the same group not be used on successive pest generations.
In practice
For growers, the useful rule is: count generations, not sprays. At 27 C a spider mite generation is about a week, so one group used for three weekly sprays has selected three generations. Rotate by group number, not by product name, because different brands often share one group. Always follow the label and local law; many groups are not legal on cannabis.
Don't confuse with
- Active ingredient: the chemical, one of possibly many in a group.
- Contact vs systemic: how it reaches the pest, not how it kills.
Tetranychus urticae, the commonest cannabis mite indoors: a 0.5 mm sap-feeder that stipples leaves pale and spins webbing, breeding fastest in hot, dry rooms.Contact products act only where the spray touches the pest; systemic products are absorbed and move inside the plant, which raises residue concerns in cannabis.The inherited ability of a pest population to survive doses of a pesticide that once controlled it, selected by repeated use of one mode of action.Integrated pest management: preventing and controlling pests by combining monitoring, prevention, cultural, biological and, as a last resort, chemical tools against set action thresholds.
