For example, when berries are injured by birds, hail, insects, or pruning, the subsequent open wounds attract fruit flies that transmit sour rot-associated microbes to the fruit. Sour rot requires the presence of wounded fruit and the interaction of fruit flies, yeast, and bacteria for symptoms to develop. A notable difference, however, is that berries with sour rot have a strong vinegar-like smell and often attract high numbers of insects, including yellowjackets and flies. Symptoms of sour rot can look similar to fungal bunch rot diseases, such as black rot (Ivey, 2016) shown in Figure 3, or Botrytis bunch rot (Ellis, 2016).

White grape varieties afflicted with sour rot appear tan to light brown in color (Figure 1), while red grape varieties appear brownish-red or brick-colored (Figure 2). Sour rot occurs on grape berries and causes discoloration, followed by berry shrivel and decomposition. Sour rot and black rot symptoms on white Traminette grapes ( Lianna Wodzicki, The Ohio State University)

Sour rot symptoms on red Pinot Noir grapes (Yvonne Woodworth, The Ohio State University)įigure 3. Many disorders, including sour rot, result in disease-like symptoms that can cause yield losses or reduce crop quality.įigure 1. Sour rot symptoms on white Traminette grapes ( Lianna Wodzicki, The Ohio State University)įigure 2. Sour rot is caused by insect-associated microbes that expedite berry decay following entry through a wound. Sour rot of grape is a disorder causing the breakdown of ripening berries rendering them unsuitable for wine production.

Sour grape