Backyard Grapes Identify & treat grapevine problems
Fungal moderate severity

Ripe rot

Colletotrichum spp.

Reddish-brown circular rot on ripening berries, often oozing salmon-pink spores.

Grape ripe rot symptoms on Kyoho berries caused by Colletotrichum viniferum: field infections (a,b) and inoculated berries at pre-veraison (c) and post-veraison (d,e) Photo: Hsieh, Shen, Huang, Tsai, Lu & Lin (2023), Plants 12(15):2873, Figure 1 MDPI Plants (via PubMed Central) CC BY 4.0
Grape ripe rot symptoms on leaves (a,b), a tendril (c) and flowers (d) of Kyoho grapevine infected by Colletotrichum viniferum Photo: Hsieh, Shen, Huang, Tsai, Lu & Lin (2023), Plants 12(15):2873, Figure 2 MDPI Plants (via PubMed Central) CC BY 4.0

Description

Ripe rot, caused by Colletotrichum fungi, is a warm-climate disease that strikes when you least want it — as the fruit sweetens toward harvest. Early infections can stay latent in green berries and only erupt once sugars rise, which is why a cluster can look clean for weeks and then rot in the final stretch of a humid summer.

The salmon-pink spore ooze in the spots is the best field clue and separates it from black rot’s dry black mummies. Because infection tracks warm rain, canopy management and timely harvest matter as much as spraying: anything that dries clusters faster cuts the losses.

What to look for

  • Circular reddish-brown spots on ripening and ripe berries.
  • Concentric rings of tiny fruiting bodies within the spots.
  • Salmon to orange-pink spore ooze on the berry in warm, humid weather.
  • Infected berries shrivel and mummify; the rot worsens as harvest nears.

Treatment options

Cultural & prevention

Start here — habits that stop problems before they spread.

  • Remove mummified berries and prune out dead wood that harbours the fungus.
  • Open the canopy so clusters dry quickly after rain and dew.
  • Harvest promptly once ripe; don't leave fruit hanging through warm wet spells.

Organic / low-toxicity

Gentler sprays and biologicals for active outbreaks.

  • Copper-based preventive sprays through the ripening period in humid climates.

Conventional fungicide / pesticide

For severe cases. Always follow the product label.

  • Protectant/systemic fungicides from veraison to harvest, observing pre-harvest intervals.

Sources

This entry is based on the references below. Read them for full detail and for spray timings and rates valid where you live.

  1. Ripe Rot of Grape — Ohio State University Extension (Ohioline)
  2. Pre-Harvest Disease Management and Late Season Bunch Rots — University of Maryland Extension
  3. Ripe Rot of Grapes — University of Kentucky, Department of Plant Pathology
  4. Insights into Grape Ripe Rot: A Focus on the Colletotrichum gloeosporioides Species Complex and Its Management Strategies — Plants (MDPI), via PMC