# Botrytis

> Botrytis cinerea, the fungus behind bud rot or grey mould, which rots dense colas from the inside in cool, humid conditions late in flower.

- Canonical: https://genetixbay.com/knowledge/glossary/botrytis.html
- Also written: bud rot, grey mould, gray mold, grey mold, Botrytis cinerea, botrytis bud rot, BBR
- 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"

*Botrytis cinerea* is a fungus that causes grey mould, called bud rot on cannabis. It attacks dense flowers from the inside, usually starting near the stem of a [cola](https://genetixbay.com/knowledge/glossary/cola.md) where moisture is trapped. Infected tissue turns brown and mushy; [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) wilt and yellow; grey, fuzzy spores appear as it progresses. It also causes stem cankers and damping-off.

## In practice

The classic sign is a single dried, discoloured leaf sticking out of an otherwise healthy cola. Pulling it reveals brown rot inside. Botrytis loves cool nights, high humidity, dew, poor airflow and wounds such as caterpillar damage. Indoors, controlling humidity and night-time [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) late in flower is the main [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md); outdoors, open-structured cultivars and early harvest before autumn rain help. Infected buds should be cut out with a margin, bagged in the room and removed; do not shake spores onto the rest of the crop. Mouldy buds should never be consumed.

## Don't confuse with

- **Powdery mildew**: white surface powder on leaves first, not internal rot.
- **Corn earworm damage**: holes and [frass](https://genetixbay.com/knowledge/glossary/frass.md), often with botrytis following.
- **Natural senescence**: yellowing fan leaves late in flower, with healthy bud tissue.

## Related terms

[Powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), [Corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [White mould](https://genetixbay.com/knowledge/glossary/white-mould.md), [Mold](https://genetixbay.com/knowledge/glossary/mold.md)

## Read more

- [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)

## Sources

1. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker
2. Utah State University Extension. Hemp bud rot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot
3. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full