Bacterial diseases in grape growing and winemaking can pose significant threats to vine health, fruit quality, and ultimately the integrity of the finished wine. In the vineyard, one of the most notable bacterial threats is Pierce’s Disease, caused by the Xylella fastidiosa bacterium, which is spread by insect vectors like the glassy-winged sharpshooter. This disease blocks the plant’s water-conducting system, leading to leaf scorch, vine dieback, and eventual vine death. It is particularly destructive in warm climates such as California and parts of the southern U.S., and currently has no cure, making vineyard management and vector control essential. Other bacterial threats in the vineyard include Crown Gall, caused by Agrobacterium tumefaciens, which forms tumor-like galls on the vine trunk and disrupts nutrient flow, weakening the vine over time. In the winery, bacterial contamination can compromise wine quality if not properly controlled. The most common concern is Acetic Acid Bacteria (Acetobacter and Gluconobacter), which convert alcohol into vinegar (acetic acid) when exposed to oxygen. This spoilage leads to volatile acidity (VA), giving the wine sharp, sour aromas reminiscent of nail polish or vinegar. Another group, Lactic Acid Bacteria—while essential for malolactic fermentation in red and some white wines—can become problematic if unmanaged, leading to off-flavors such as mousiness, ropiness, or excessive diacetyl (buttery notes). Poor hygiene, improper sulfur levels, or uncontrolled oxygen exposure are common triggers for bacterial spoilage in the cellar. Preventing bacterial issues requires careful attention throughout both the vineyard and winemaking process. In the vineyard, disease-resistant rootstocks, pest monitoring, and good sanitation practices help limit the spread of bacterial pathogens. In the winery, managing oxygen, maintaining clean equipment, controlling temperature, and using appropriate sulfur dioxide levels are critical to suppressing unwanted bacterial activity.