Since first being reported in Anaheim, California, in the 1880s, Pierce’s disease of the grapevine has spread across the state, the US, and Europe. Triggered by the bacterium Xylella fastidiosa, it clogs tubes called xylem that transport water and nutrients, leading to plant death. Recent estimates suggest the disease causes over $100 million in lost revenue and prevention-related costs in California each year.

In a study published last December, Rausser College researchers identified a 120-year-old grapevine cutting at UC Davis that still contained traces of X. fastidiosa DNA from the early 1900s. By comparing that genome to more than 330 contemporary strains of X. fastidiosa, they reconstructed the history of how the pathogen first arrived in California. 

Scientists had long assumed that X. fastidiosa was introduced to California in the 1880s, when many species of grapes were brought to the state to establish vineyards. But the study’s genomic data suggests that the pathogen actually arrived in the US nearly 150 years earlier, around 1740, from Central America. The data further suggests that the disease in California arose from not one but at least three separate introductions of the pathogen. 

“This occurred over 250 years ago but is still relevant to understanding the global spread of plant pathogens today,” said Monica Donegan, a graduate student in the Department of Environmental Science, Policy, and Management (ESPM) who co-authored the study with postdoctoral scholar Alexandra Kahn, PhD ’23 ESPM. “Assumptions about the routes and timing of pathogen introduction can impact things like international trade policies and quarantines for plant pathogens.”

The fact that there were likely three separate introductions of X. fastidiosa suggests that multiple, genetically distinct, pathogen populations may exist in California. Like different variants of SARS-CoV-2, they may cause similar symptoms but respond differently to stressors like climate change. “These biological differences, even if small, can be meaningful when it comes to disease management,” said Professor Rodrigo Almeida, the study’s senior author. 

In recent decades, X. fastidiosa has spread from the U.S. and Latin America to other countries, including Portugal, Spain, Italy, Israel and Taiwan. Knowing the evolutionary rate of the pathogen can also help researchers estimate the timing of these introductions and prevent further spread.

— adapted from an article by Kara Manke

“Literally off the charts.”

— John Battles, Profesor, Environmental Science, Policy, and Management

Battles spoke to CalMatters in January, explaining how the vapor pressure deficit—a combination of high air temperature and low relative humidity—greatly exceeded norms and helped fuel devastating wildfires in Southern California that month. He said the likely role of climate change in the weather extremes that clobbered California makes direct human intervention almost negligible, and better planning key to improving wildfire safety. Since 2021, Battles has helped develop an open-source tool that makes it easier to access, visualize, and analyze data needed to plan landscape-scale hazard reduction projects while protecting biodiversity, watershed health, and carbon storage.

“It would be a speed bump in the road, but if the US goes all electric in 2090 rather than 2050…a lot of carbon would be emitted in that time.”

— Joe Shapiro, Associate Professor, Agricultural and Resource Economics

Shapiro spoke with The Guardian in February about potential impacts if the Biden-era electric vehicle tax credit were to be overturned by the Trump administration. A study he co-authored shows that while a growing number of people would still go electric, the total number of EV cars sold would shrink by more than 300,000 a year compared to if the incentive stayed in place. His comments were informed by research on EVs and the Inflation Reduction Act, which was published as a working paper by the Energy Institute at Haas last December.

“The FAIR Plan just wasn’t designed to be a permanent solution for a large swath of the market."

— Meredith Fowlie, Professor, Agricultural and Resource Economics 

 In a January episode of NPR’s Planet Money, Fowlie expressed concern that California homeowners enrolled in the FAIR Plan, the state’s home insurance provider of last resort, would wind up stuck in the program due to private insurers refusing to issue policies in fire-prone areas.