# Pesticide resistance

> 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.

- Canonical: https://genetixbay.com/knowledge/glossary/pesticide-resistance.html
- Also written: resistance, insecticide resistance, miticide resistance, fungicide resistance, mode of action rotation, IRAC, FRAC
- 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"

Pesticide resistance is a genetic change in a pest or pathogen population that lets it survive a product that used to work. It is selected, not created: every application kills susceptible individuals and leaves the few resistant ones to breed. Pests with short generations and huge populations, such as [two-spotted spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [western flower thrips](https://genetixbay.com/knowledge/glossary/thrips.md), *Bemisia* [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), develop resistance fastest.

## In practice

Growers slow resistance by rotating products with different modes of action rather than different brand names, since many products share an active ingredient. Industry groups classify actives by [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md): the Insecticide Resistance Action Committee (IRAC) for insecticides and miticides, and the Fungicide Resistance Action Committee (FRAC) for fungicides. Other habits: use full label rates, do not spray when scouting says it is unnecessary, and lean on biological and [cultural controls](https://genetixbay.com/knowledge/glossary/cultural-control.md), which pests cannot easily evolve around. "It stopped working" after a few applications usually means poor coverage, wrong identification or resistance.

## Don't confuse with

- **Plant disease resistance**: a crop trait, such as mildew-resistance [genes](https://genetixbay.com/knowledge/glossary/gene.md).
- **Tolerance**: a plant coping with damage without losing yield.

## Related terms

[Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md)

## Read more

- [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md)

## Sources

1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html
2. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html