# Bitter rot

- URL: https://backyardgrapes.com/diseases/bitter-rot/
- Scientific name: Greeneria uvicola
- Category: Fungal
- Affects: Fruit clusters
- Severity: moderate
- Favored by: Warm, humid, rainy weather near harvest; overwinters in mummies and dead wood.
- Easily confused with: Ripe rot, Black rot, Botrytis bunch rot (grey mould)

**Summary:** A late-season berry rot that softens ripe fruit and leaves it bitter — often riding in behind other rots.

**What to look for:**
- Soft, browning rot on ripe and ripening berries, usually starting near the stem end.
- Whole berries collapse; a bitter taste in affected fruit and any wine made from it.
- Fine dark fruiting bodies over the rotted surface, sometimes with grey spore masses.
- Rotted berries dry to mummies that cling to the cluster.

**Treatment — Cultural / prevention:**
- Remove mummified berries and prune out dead wood, the main overwintering sites.
- Open the canopy so clusters dry quickly after rain.
- Harvest promptly and avoid leaving ripe fruit through warm, wet spells.

**Treatment — Organic / low-toxicity:**
- Copper-based preventive sprays through ripening in humid climates.

**Treatment — Conventional (chemical):**
- Late-season protectant fungicides overlap with black-rot and ripe-rot programs; mind pre-harvest intervals.

Bitter rot (*Greeneria uvicola*) is a warm-climate berry rot that shows up late, as the
fruit ripens, and — true to its name — leaves affected berries and any resulting wine
tasting bitter. It often travels with the other warm-season rots and takes advantage of
berries already weakened by black rot, ripe rot, or feeding injury, so it's easy to miss
as a distinct problem.

The fungus overwinters in mummified berries and dead wood, then spreads in warm rain, so
the controls are the familiar ones for the rot complex: sanitation, an open canopy that
dries fast, prompt harvest, and preventive sprays timed to the ripening window. Growers in
hot, humid regions should watch for it; in cool, dry climates it is rarely a concern.

**Image credits:**
- Bitter rot on a grape cluster — [Photo: Andy Allen, University of Missouri, eXtension (Grapes community of practice)](https://web.archive.org/web/20150111202741/http://www.extension.org/pages/31135/bitter-rot-of-grapes)
- Grape berries infected with bitter rot — [Ohio State University Extension (Ohioline)](https://ohioline.osu.edu/factsheet/plpath-fru-08)

**Sources:**
- [Bitter Rot of Grape](https://ohioline.osu.edu/factsheet/plpath-fru-08) — Ohio State University Extension
- [Bitter Rot of Grapes](https://fruitscout.mgcafe.uky.edu/bitter-rot-grapes) — University of Kentucky Department of Plant Pathology
- [North Carolina Winegrape Grower's Guide, Chapter 8: Pest Management](https://content.ces.ncsu.edu/north-carolina-winegrape-growers-guide/chapter-8-pest-management) — NC State Extension