# Insecticidal soap

> Potassium salts of fatty acids sprayed to kill soft-bodied pests such as aphids, mites and whitefly nymphs on contact by disrupting their cell membranes.

- Canonical: https://genetixbay.com/knowledge/glossary/insecticidal-soap.html
- Also written: insecticidal soaps, potassium salts of fatty acids, soap spray, potassium soap, fatty acid soap
- 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"

Insecticidal soap is a spray of potassium salts of fatty acids. It kills soft-bodied insects and [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) that it wets directly, by disrupting the cell membranes of the outer body and removing protective waxes. Once dry it has no residual activity, and it is relatively low in [toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) to people and mammals.

## In practice

Growers use soap in veg against [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), spider mites, whitefly nymphs, thrips larvae and [mealybug crawlers](https://genetixbay.com/knowledge/glossary/crawler.md). It only works where it touches, so leaf undersides must be soaked, and repeat sprays every few days catch hatching eggs. [Hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md) reduces [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md); soft or [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) helps. It can scorch leaves of some cultivars, in heat or under strong light, so test on a few leaves first. Dish detergents are not the same product: they are formulated differently and can damage leaves. Keep soap off flowers. Check what is registered for cannabis locally.

## Don't confuse with

- **Horticultural oil**: smothers pests; can be combined, but phytotoxicity risk rises.
- **Surfactant or wetting agent**: improves spreading, not a pesticide by itself.
- **Dish soap**: a cleaning product, not a registered insecticide.

## Related terms

[Horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md), [Neem oil](https://genetixbay.com/knowledge/glossary/neem-oil.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md)

## Read more

- [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md)

## Sources

1. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html
2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html