# Botrytis bunch rot (grey mould)

- URL: https://backyardgrapes.com/diseases/botrytis-bunch-rot/
- Scientific name: Botrytis cinerea
- Category: Fungal
- Affects: Fruit clusters
- Severity: moderate
- Favored by: Cool, damp, humid weather on ripening or injured fruit.
- Easily confused with: Powdery mildew, Downy mildew, Sour rot, Ripe rot, Bitter rot

**Summary:** Fuzzy grey mould that rots ripening clusters, especially after rain near harvest.

**What to look for:**
- Soft, brown, watery rot on ripening berries.
- A fuzzy grey-brown mould coating that puffs into dust when touched.
- Rot spreads berry-to-berry through a tight cluster.
- Splits, wounds, and bird/insect damage are common entry points.

**Treatment — Cultural / prevention:**
- Open the fruit-zone canopy (leaf removal) so clusters dry quickly.
- Choose loose-clustered varieties; thin tight clusters.
- Control powdery mildew and insects that wound berries — the usual entry points.
- Harvest promptly and discard rotten berries.

**Treatment — Organic / low-toxicity:**
- Reduce humidity and injuries first; sprays are secondary for grey mould.

**Treatment — Conventional (chemical):**
- Botrytis-specific fungicides at bloom, bunch closure, veraison, and pre-harvest.
- Rotate FRAC groups — Botrytis develops resistance quickly.

Botrytis (*Botrytis cinerea*) is an opportunist: it attacks fruit that is already
ripe, split, or wounded, and races through tight clusters in damp weather. On wine
grapes in the right dry conditions it becomes the prized "noble rot", but for a home
grower it usually just means lost fruit.

Because it exploits injuries, the best control is indirect — keep clusters loose and
dry, and stop the powdery mildew, birds, and insects that crack the berries open in
the first place.

**Image credits:**
- Chardonnay grapes with Botrytis infection in the middle of the cluster — [Photo: Patty Skinkis, Oregon State University, Oregon State University Extension Service](https://extension.oregonstate.edu/crop-production/wine-grapes/how-prevent-botrytis-bunch-rot-vineyard)
- Severe Botrytis bunch rot on grape clusters of cv. Vignoles — [Photo: Wayne Wilcox, Cornell University, Appellation Cornell (Research Focus 2016-4)](https://web.archive.org/web/20180613032413/https://grapesandwine.cals.cornell.edu/sites/grapesandwine.cals.cornell.edu/files/shared/documents/Research%20Focus%202016-4.pdf)
- Typical symptoms of Botrytis bunch rot on a grape cluster — [Photo: Timothy Miles, MSU, Michigan State University Extension](https://www.canr.msu.edu/news/managing-botrytis-bunch-rot-in-grapes)

**Sources:**
- [Botrytis Bunch Rot in Commercial Washington Grape Production: Biology and Disease Management](https://pubs.extension.wsu.edu/botrytis-bunch-rot-in-commercial-grape-production-biology-and-disease-management) — Washington State University Extension
- [How to prevent Botrytis bunch rot in the vineyard](https://extension.oregonstate.edu/crop-production/wine-grapes/how-prevent-botrytis-bunch-rot-vineyard) — Oregon State University Extension Service
- [Botrytis Bunch Rot / Grape / Agriculture: Pest Management Guidelines](https://ipm.ucanr.edu/agriculture/grape/botrytis-bunch-rot/) — UC Statewide IPM Program (UC ANR)
- [Botrytis Bunch Rot on Grapes in Home Gardens](https://extension.psu.edu/botrytis-bunch-rot-on-grapes-in-home-gardens) — Penn State Extension