What is Pierce’s disease, and how does it affect wine grapes?
Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
What is Pierce’s disease, and how does it affect wine grapes?
—Krysten, San Diego
Dear Krysten,
Pierce’s disease is caused by the bacterium Xylella fastidiosa and affects the water-conducting system, or xylem, of a grapevine. It’s spread from plant to plant by insects known as sharpshooters. Once infected by these vineyard pests, plants have trouble transporting water to crucial places. Leaves start looking scorched, dry up and fall off, and eventually—in as quickly as a year or two—the bacteria will kill the plant. Pierce’s disease has been a problem for over a century, and it remains an issue in California, where it was discovered, and beyond.
There is no cure, and infected vines need to be removed. There are some rootstocks and native varieties that are resistant, and last year, scientists at UC Davis discovered particular genes that provide resistance. There’s hope that they could be introduced into grapevines to protect them from the disease, and that new grape varieties may provide one path forward. Other researchers have tried targeting the bacteria with a type of virus called a bacteriophage. Research into how to prevent, manage and hopefully cure the disease is ongoing.
Pierce’s disease also affects plants beyond grapevines. When it happens to almonds, it’s called “almond leaf scorch,” and when it attacks peach trees it’s known as “phony peach disease” (harsh!). It can also affect oleander, plums, citrus and other plants.
—Dr. Vinny
