# Mode of action

> How a pesticide kills its target, grouped by IRAC into numbered classes; rotating between groups across pest generations slows resistance.

- Canonical: https://genetixbay.com/knowledge/glossary/mode-of-action.html
- Also written: MoA, IRAC group, mode of action group
- Glossary category: Pests and diseases · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

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](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) 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.

## Related terms

[Pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md)

## Read more

- [Integrated pest management (IPM) for cannabis: a complete programme for home and small commercial growers](https://genetixbay.com/knowledge/pests/integrated-pest-management-program.md)
- [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md)

## Sources

1. Insecticide Resistance Action Committee. Mode of Action classification. https://irac-online.org/modes-of-action/