Justin D. Tanner, PhD, began his role as the UCCE Northern San Joaquin County Viticulture Farm Advisor for the Lodi area on January 3, 2023, following the footsteps of Paul Verdegaal’s over a 30-year term. Tanner currently serves all of San Joaquin County and the portion of southern Sacramento County that encompasses the Lodi AVA, in addition to vineyards in Stanislaus County. He is based in Stockton at the Robert J. Cabral Agriculture Center. Tanner’s responsibilities include implementing extension education and applied research to address high-priority issues related to winegrape production. He is working closely with growers, industry, the Lodi Winegrape Commission, and PCAs in the region. One of his most important annual tasks is to help the Lodi Chamber of Commerce’s Agribusiness Committee organize the morning educational program for Lodi Grape Day held in early February.

Before becoming a UC Farm Advisor, Tanner was a post-doctoral scholar and researcher in the UC Davis Department of Viticulture and Enology designing and implementing research projects to investigate factors that affect winegrape production. Field research projects included: investigating the effects of cluster thinning and irrigation practices to mitigate grapevine red blotch virus impacts; evaluating different combinations of rootstocks and scions for production suitability; and evaluating trellis systems and the use of shade films for mitigating heat impacts on vine canopies and grape quality.

Tanner completed his PhD in Horticulture at Colorado State University (CSU), Fort Collins in 2020. He was a research associate at CSU, and a biological science technician with the nearby U.S. Department of Agriculture Agricultural Research Service at the National Laboratory for Genetic Resources Preservation in Fort Collins. His work in those positions involved developing more efficient methods to preserve and store germplasm of Vitis cultivars and other perennial fruit crops that included cryptopreservation methods. A native of Texas, he completed his MS degree in Horticulture and his BS degree in Agriculture, both at Texas A&M University in Kingsville.

Tanner said, “I look forward to meeting with grape growers at their vineyard sites and learning about the issues they face to address the needs of the highest priority in the region.” Anticipated projects include helping growers with more efficient soil mapping to delineate different vineyard management zones, helping growers calculate more accurate yield estimates, and conducting rootstock trials.

Dr. Tanner is pictured third from left with fellow members of the Lodi Winegrape Commission’s Grapevine Rootstock Research Focus Group, other scientists, and growers at the UC Oakville Experiment Station in June 2023 during the American Society of Enology and Viticulture annual conference. Dr. Tanner and Maria Zumkeller (LangeTwins) both conducted field trials in Oakville before taking on their current roles in Lodi. Photo taken by Stephanie Bolton.


We had the chance to interview Justin Tanner, PhD, about his first year. Continue to read below to see how it went.

How has your first year as Lodi’s UC Cooperative Extension Viticulture Advisor gone?

In my first year as the San Joaquin County CE Viticulture Advisor, despite the challenges posed by an unusually cool and wet growing season, it has been a rewarding experience. I’ve had the opportunity to become acquainted with the region and gain insight into the unique production challenges that winegrape growers in the northern San Joaquin Valley face.

In your opinion, what do you see as the biggest challenges for Lodi growers?

There is no shortage of challenges facing winegrape production in San Joaquin County. These include managing invasive pests like the vine mealybug, controlling the spread of viruses such as Grapevine Leafroll associated Virus, and responding to climatic challenges like heatwaves, droughts, and floods, as well as late spring and early fall frosts, to name a few. However, one of the major concerns for me is the market challenges. The price per ton for winegrapes in our region has remained mostly flat while production costs have steadily increased over the last few years. This economic pressure is a significant hurdle for the economic sustainability of many small growers. Balancing quality and yield is not as concerning as balancing the books when profit margins are thin. Many growers are feeling the financial strain, and the higher-than-average production this year has intensified the competition, exacerbating the situation.

In your opinion, what do you see as opportunities for Lodi growers in the future?

Looking ahead, I see opportunities for Lodi growers to optimize production practices to reduce production costs and inputs while maintaining quality and yield targets. Diversifying production to reduce competition is another avenue to explore. The adoption of automated and mechanized practices that reduce the demand for labor will be key to staying competitive in the future.

What do you hope to accomplish with Lodi growers over the next several years?

Over the next several years, I aim to contribute to the success of the industry by assisting growers in identifying and implementing climate-resilient vineyard adaptations. These adaptations are designed to reduce vine stress, disease pressure, and management costs while upholding the long-standing and hard-earned reputation of the Lodi area as producers of high-quality winegrapes. I plan to achieve this through a focused extension program that centers on listening to and collaborating with Lodi growers to identify and address their most pressing needs. To this end, I am currently conducting a needs assessment and seeking feedback from our growers, PCAs, and consultants. This short survey will only take a few minutes to complete and is completely confidential. Your responses are highly valued and appreciated. See link below.

Justin Tanner, PhD, can be contacted by phone at 209.953.6119 and by email at Please fill out the survey HERE or scan the QR code below.

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