# Black rot

- URL: https://backyardgrapes.com/diseases/black-rot/
- Scientific name: Guignardia bidwellii
- Category: Fungal
- Affects: Leaves, Fruit clusters
- Severity: high
- Favored by: Warm and wet spring/early summer; overwinters in mummies and canes.
- Easily confused with: Downy mildew, Phomopsis cane & leaf spot, Ripe rot

**Summary:** Tan leaf spots ringed with black dots, and berries that shrivel into hard black mummies.

**What to look for:**
- Small tan/brown circular leaf spots with a dark border and tiny black specks in the centre.
- Berries develop a pale spot, then rot, shrivel, and harden into black "mummies".
- Mummified berries stay attached to the cluster.
- Dark sunken lesions can also girdle young shoots.

**Treatment — Cultural / prevention:**
- Remove and destroy every mummified berry and infected cane — this is the main source.
- Rake up fallen debris; keep the canopy open and dry.
- Prune out cane lesions during dormancy.

**Treatment — Organic / low-toxicity:**
- Copper or sulphur-based preventive sprays from early shoot growth through fruit set.

**Treatment — Conventional (chemical):**
- Protectant/systemic fungicides (e.g. mancozeb early, then labelled products) from bud break to veraison.
- The critical window is bloom to a few weeks after fruit set.

Black rot (*Guignardia bidwellii*) can destroy an entire crop in a wet year, yet is
very manageable with sanitation. The disease survives winter almost entirely in the
shrivelled "mummies" left hanging on the vine and on the ground — so removing them is
the highest-impact thing a home grower can do.

Infections start on the leaves in spring, but the damage that matters happens on the
young berries. Once a berry turns into a hard black mummy it is a spore factory for
next season.

**Image credits:**
- Black rot leaf lesions: tan spots with a dark border and black pycnidia — [Photo: Cesar Calderon, USDA APHIS PPQ, Bugwood.org, Bugwood.org](https://www.ipmimages.org/browse/detail.cfm?imgnum=5538188) (CC BY-NC 3.0 US)
- Berries at three stages: healthy, soft brown rot, and hard black mummies — [Photo: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org, Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Guignardia_bidwellii_(black_rot)_on_grape_2.jpg) (Public domain)
- Cluster with about half the berries shrivelled into black rot mummies — [Photo: University of Georgia Plant Pathology, Bugwood.org, Bugwood.org](https://www.ipmimages.org/browse/detail.cfm?imgnum=1495049) (CC BY-NC 3.0 US)
- Black rot (Guignardia bidwellii) symptoms on grapevine berries and leaf — [Photo: Daniel Molitor, Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Guignardia_bidwellii_04.jpg) (CC BY 2.0 DE)

**Sources:**
- [Grape Black Rot](https://ohioline.osu.edu/factsheet/plpath-fru-24) — Ohio State University Extension
- [Black Rot of Grape](https://extension.umaine.edu/ipm/ipddl/publications/5106e/) — University of Maine Cooperative Extension
- [Black rot on grapes (Guignardia bidwellii)](https://blog-fruit-vegetable-ipm.extension.umn.edu/2026/06/black-rot-on-grapes-guignardia-bidwellii.html) — University of Minnesota Extension
- [Online Guide to Grapevine Diseases: Black rot](https://www.arec.vaes.vt.edu/content/dam/arec_vaes_vt_edu/alson-h-smith/grapes/pathology/extension/factsheets/black-rot.pdf) — Virginia Tech, AHS Agricultural Research and Extension Center