# Root rot

> Decay of roots by pathogens such as Pythium, Fusarium, Rhizoctonia or Phytophthora, usually triggered by low oxygen, heat and waterlogging around the roots.

- Canonical: https://genetixbay.com/knowledge/glossary/root-rot.html
- Also written: root disease, brown roots, rotting roots, crown rot, root and crown rot
- 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"

Root rot is the umbrella term for decay of a plant's roots by soil-borne or water-borne pathogens. On cannabis the main agents are the water mould *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*, *[Fusarium](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md)* species, *[Rhizoctonia solani](https://genetixbay.com/knowledge/glossary/damping-off.md)* and occasionally *Phytophthora*. Healthy roots are white to cream and firm; rotting roots turn brown, soft and hollow, and the outer layer slides off. Rot at the base of the stem is called crown rot.

## In practice

Root rot usually follows a weakness: warm water, little dissolved oxygen, [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) pots, compacted media or salt damage. In hydroponics, solution held above roughly 24-26 °C (75-79 °F) with poor aeration is the classic setup. Plants droop in the heat of the day, yellow, stall and do not respond to feed. Growers diagnose by pulling a plant and smelling and pressing the roots: a sour or rotten smell and slime mean pathogens. Fixing the cause, removing badly hit plants, cleaning the system and restoring oxygen come before any product.

## Don't confuse with

- **Tea-coloured roots**: stained by additives or organic inputs but still firm.
- **Overwatering**: low oxygen alone, reversible before pathogens take hold.
- **Root aphids**: insects on roots, not decay.

## Related terms

[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md), [Fusarium wilt](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md), [Biofilm](https://genetixbay.com/knowledge/glossary/biofilm.md), [Damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md)

## Read more

- [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md)
- [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)

## Sources

1. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466
2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Root and Crown Rot. https://pnwhandbooks.org/node/12931
3. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic production (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf