Sour rot is a condition characterized by the rapid decomposition of ripening berries. Berries affected by sour rot exude a vinegar-like odor. Different types of bacteria are associated with the disease. However, the acetic acid bacteria, Acetobacter spp. and Gluconobacter spp. are always associated with sour rot. Sour rot typically develops in berries injured by other pathogens, insects, birds, or hail. Berries are most susceptible to sour rot during wet summers.
Signs and Symptoms
Sour rot on white grape variety
Sour rot on red grape variety
Infected berries of white varieties turn light chestnut brown (image above, Photo courtesy- Purdue Univ.), whereas infected berries of red varieties turn brick or purplish red (image above, Photo courtesy- extension.org). The flesh of infected berries degrades rapidly becoming soft and watery with a strong vinegar-like odor. The skin of the infected berries becomes thin and eventually cracks and releasing juices. Cracked berries attract flies, yellow jackets, and other insects to the clusters.
Sour Rot Management
Sanitation and Cultural Practices:
The primary strategy for managing sour rot is to minimize berry injuries. Insects such as flies, yellow jackets, other wasps and grape berry moths should be controlled. Bird decoys or netting can deter birds.
- Canopy management and removal of leaves to improve circulation and reduce humidity can slow disease development.
Fungicides are not effective for managing sour rot.