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Monitoring and Building Soil Health in California Vineyards

By
Charlotte Decock | Associate Professor, Grimm Family Center for Organic Production and Research, California Polytechnic State University, San Luis Obispo, Lauren Picone| Masters Student, Environmental Sciences and Management, California Polytechnic State University, San Luis Obispo, Priya Verma | Associate Professor, Dept. of Natural Resources Management and Environmental Sciences, California Polytechnic State University, San Luis Obispo, Matt Grieshop | Director, Grimm Family Center for Organic Production and Research, California Polytechnic State University, San Luis Obispo and Cristina Lazcano | Associate Professor, Dept. of Land, Air and Water Resources, UC Davis
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Figure 1. Example of a vineyard soil health scoring function modeled after Cornell’s CASH framework.

Soil health is central to sustainable agriculture and a key goal of regenerative and organic farming. Practices like the application of organic amendments, cover cropping, reduced tillage and livestock integration are promoted to improve soil health. Traditionally, sustainability or organic certifications have relied on the adoption of certain practices for monitoring and verification. However, newer regenerative agriculture certifications are introducing requirements for direct monitoring of soil health.

This shift raises important questions: How should soil health be measured and rated? How can these ratings inform management decisions? Should soil health ratings and interpretations be tailored to specific crops and regions?

To explore these issues, we conducted a case study analysis of 87 vineyard blocks across California, representing diverse management histories. This study aims to shed light on the link between regenerative agriculture and soil health monitoring in the context of California winegrape production.

How to Measure Soil Health?
Numerous soil health assessment frameworks have been developed globally, each varying in practicality, sensitivity, and interpretability. These frameworks typically include indicators of physical, chemical and biological soil properties. In the U.S., commercial laboratories offer soil health testing packages priced between $55 to $165 per sample. However, the methods and indicators used in these packages vary, making it challenging to compare results across tests.

The Soil Health Institute evaluated 30 soil health indicators across 124 long-term experiments in Northern America and recommended a core suite of practical and affordable measurements: soil organic carbon (SOC), carbon mineralization potential (MinC) and aggregate stability index (ASI). These indicators were chosen for their response to management practices across a wide range of soils, climates and production systems. In our study, we focused on these three indicators due to growing interest among California growers and laboratories in the Soil Health Institute’s recommendations.

Interpreting Soil Health Measurements
When evaluating soil health indicators, it is common to wonder: Is a MinC value of 50 mg CO2-C/kg soil/day good or bad? Last year, my soil had 1.2% SOC, but this year, the lab results showed 1.15%. Does this indicate a significant decline in soil health? What is the maximum aggregate stability achievable in my soil?

Answering these questions requires an understanding of expected soil health indicator ranges, the soil’s inherent potential and typical sampling and analysis errors. To address these complexities, Cornell’s Comprehensive Soil Health Assessment (CASH) developed scoring functions for various soil health indicators using samples from the Mid-Atlantic, Midwest, and Northeast U.S. regions.

The CASH scoring system assigns scores based on the percentage of samples with equal or lower values. For example, a score of 80% means your result is better than 80% of the reference dataset (Fig. 1). The system also accounts for soil texture, recognizing its role in influencing and sometimes constraining soil health outcomes.

Color ranges on the chart help evaluate whether soil health values differ significantly. Substantial improvements over time can shift soil into better color zones, with dark green zone indicating the soil has likely reached its potential. Though other rating and benchmarking frameworks have been proposed, we based our scoring system for California vineyards on the CASH framework, given its simplicity and clarity.

Rating Curves for California Vineyards
To develop scoring functions for California vineyards, we collaborated with winegrape growers who provided soil samples from vineyard blocks of red varietals. These blocks included those that had adopted cover cropping, compost application and no till or grazing for at least five years as well as blocks where none of these practices had been adopted for at least 10 years. Soil samples were collected from areas next to the vine and at the center of the drive rows. Additionally, growers completed a detailed survey about their practice implementation.

Figure 2. Map of participating vineyard blocks and sample locations. A total of 87 vineyard blocks were sampled from as far north as the Russian River Valley AVA and down to the Happy Canyon of Santa Barbara AVA.

The dataset includes a total of 87 vineyard blocks (Fig. 2), with various combinations of practice adoption, ranging between 0 and 27 years. Thus, the scoring functions represent how soil health values may improve with the adoption of regenerative practices across a broad range of soil types and microclimates (Fig. 3).

Figure 3. Soil health scoring functions for soil organic carbon (SOC), mineralizable carbon (MinC) and aggregate stability index (ASI) for California vineyard soils.

Like other frameworks, our scoring functions account for soil texture. Clayey soils are known to store more carbon and support greater microbial activity compared to sandier soils. Consequently, coarse-textured soils achieve high scores at lower SOC and MinC values than fine-textured soils. For ASI, values trend higher in coarse-textured soils because they are less prone to dispersion when slaked.

Comparing the ranges of SOC, MinC and ASI in our study to those reported in the literature supports the idea that building soil health may face more biophysical limitations in mediterranean regions compared to temperate climate zones. This highlights the importance of developing scoring functions tailored to specific regions and crops.

Monitoring Soil Health for Adaptive Management
For soil health scoring systems to be useful for growers, they must be sensitive to changes in management practices within an operation. To test this, we compiled individualized reports for each participating grower and evaluated whether the scoring system could detect differences in management history among samples from the same grower (Fig. 3).

The study involved 12 growers, each providing samples from 2 to 17 vineyard blocks. Overall, the scoring system successfully identified differences between vineyard blocks submitted by the same grower. Growers reported the scores either reinforced their management goals or highlighted areas where soil health management fell short of their targets. These findings demonstrate the soil health assessment framework can effectively support adaptive soil management in vineyards (Fig. 4).

Figure 4. Anonymized grower report example. Soil health ratings are greater in the vineyard blocks with adoption of multiple practices compared to vineyard blocks with only cover crops.

Successful Paths to a Healthy Vineyard Soil
Adopting soil health practices, such as cover cropping, composting, reduced tillage and grazing, involves costs and uncertainties, often with unclear timelines for measurable impacts. We used quantitative comparative analysis to explore conditions leading to soil health scores above 60%, revealing complex causal relationships.

Long-term cover cropping (10+ years) emerged as the most important factor for achieving high soil health scores, especially when combined with another regenerative practice. This benefit extended across the vineyard floor, improving soil health in both alleys and under-vine areas. Notably, the integration of livestock was identified as a key practice for accelerating soil health improvements, yielding measurable benefits even after less than 10 years of cover cropping.

Achieving high ASI and MinC scores appeared to require long-term adoption of more practices compared to high SOC scores. However, our findings suggest tailoring the right combination of practices to specific environmental conditions is more important than simply increasing the number of practices used.

Practical Implications for Vineyard Managers in California
Our study provides proof-of-concept for the use of SOC, MinC and ASI to evaluate vineyard soil health in California, supported by practical soil health scoring functions. This approach can help monitor vineyard soil health and inform adaptive management strategies. Given the variability of soil type and microclimate, growers are encouraged to experiment with different strategies to determine what works best for their conditions. While monitoring can identify effective practices, building soil health is a slow process that often takes over a decade. This underscores the need for long-term commitment, with monitoring intervals every few years being sufficient.

Winegrape growers can use our rating curves as a reference to monitor soil health. For SOC testing, ensure that labs report SOC specifically, rather than total carbon, especially in calcareous soils where high carbonates can skew results. Many labs also offer MinC (soil respiration) testing; our scoring functions are applicable as long as results are expressed in mg CO₂-C kg–¹ soil d–¹, regardless of preparation or incubation duration (one to four days). For ASI, only results obtained using the Soil Health Institute’s SLAKES test are compatible with our scoring functions. Growers can work with labs that use SLAKES or measure ASI in-house via the SLAKES app available at soilhealthinstitute.org/our-work/initiatives/slakes/.

Future Work
The scoring functions in our study are based on data from 87 vineyard blocks and reflect the progression in soil health scores that may occur over time with the implementation of a soil health management strategy. As more data becomes available, these scoring functions could be refined further to address specific soil types or microclimates.

Since the effectiveness of soil health management practices depends on factors like implementation (e.g., cover crop species, compost type, etc.) as well as soil type and environmental conditions, future research should focus on identifying the most effective combinations of practices for specific contexts.

Finally, soil health is rarely a management goal on its own. Future research should quantify the impact of improved soil health on key agronomic and environmental outcomes, including yield, grape quality, pest and disease pressure, pollution from leaching and runoff, biodiversity and climate change adaptation and mitigation.

This project was funded by the CDFA Specialty Crops Block Grant and the Foundation for Food and Agriculture Research. We thank all growers who participated in this study.

References
Hughes, H. M. et al. Towards a farmer-feasible soil health assessment that is globally applicable. Journal of Environmental Management 345, 118582 (2023).

Feeney, C. J. et al. Development of soil health benchmarks for managed and semi-natural landscapes. Science of The Total Environment 886, 163973 (2023).

Bünemann, E. B. Soil quality – A critical review. Soil Biology and Biochemistry 120, 105–125 (2018).

Shi. Recommended Measurements for Scaling Soil Health Assessment. (2024).

Fine, A. K., van Es, H. M. & Schindelbeck, R. R. Statistics, scoring functions, and regional analysis of a comprehensive soil health database. Soil Science Society of America Journal 81, 589–601 (2017).

Moebius-Clune, B. N. et al. Comprehensive Assessment of Soil Health – The Cornell Framework Manual. (2016).

Maharjan, B., Das, S. & Acharya, B. S. Soil Health Gap: A concept to establish a benchmark for soil health management. Global Ecology and Conservation 23, e01116 (2020).

Six, J., Doetterl, S., Laub, M., Müller, C. R. & Van de Broek, M. The six rights of how and when to test for soil C saturation. SOIL 10, 275–279 (2024).

Müller, T. & Höper, H. Soil organic matter turnover as a function of the soil clay content: consequences for model applications. Soil Biology and Biochemistry 36, 877–888 (2004).

Nunes, M. R. et al. SHAPEv1.0 Scoring curves and peer group benchmarks for dynamic soil health indicators. Soil Science Society of America Journal 88, 858–875 (2024).

Fajardo, M., McBratney, Alex. B., Field, D. J. & Minasny, B. Soil slaking assessment using image recognition. Soil and Tillage Research 163, 119–129 (2016).

Slakes: A Free Smartphone App to Measure Aggregate Stability. Soil Health Institute (2024). https://soilhealthinstitute.org/our-work/initiatives/slakes/#overview

Market Research Shows How to Win Up-and-Coming Consumers, Widen Wine’s Multicultural Appeal

By
Pam Strayer | Contributing Writer
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61% of those studied preferred sustainable, family-owned brands, with 58% explicitly preferring organic (photo courtesy Maverick Farming.)

As marketers know, the adage “markets are conversations” still rings true, and a remarkably in-depth new study, “Attracting More Young Adults and Multicultural Consumers to Wine,” released December 17 by the Wine Market Council, underscores that in spades.

Currently, wine marketing can sometimes trend towards inertia. Example: With 68 million (out of 170 million) wine drinkers on TikTok, brands are intimidated by (and often absent from) the media platform favored by their newest customers. Innovation is lacking. Are these problems solvable?

Yes, according to the latest data from Mike Lakusta, CEO of Ethnifacts, and the Wine Market Council, which studied 1,816 consumers in their 20s and 30s to find out how that wine currently appeals, or does not, to younger consumers who are increasingly more diverse.

Said Lakusta, “We purposely oversampled the multicultural populations. About two-thirds of the people in this study were Hispanic, Black, Asian or other versus Caucasian, which is about 50% of this age cohort. For the purposes of this study, about two thirds was multicultural,” because researchers wanted to explore these segments in greater detail.

In addition, “20% of the surveys for Hispanics were done in Spanish,” he said, “so we could make sure we were getting good representation, and that is about the percentage of Spanish dominant in the country.”

While the mountain of data substantiates current perceptions, the authors found many eye-opening ways to improve wine marketing at every level.

Inclusion as a Game Changer: Overcoming the Culture Gap
With the multicultural demographics of the U.S alcoholic beverage drinker expanding, the data clearly shows a gap exists. While 52% of respondents found wine relaxing, only 12% felt wine was connected to their culture.

54% said they preferred to buy wine from someone of their own culture.

Therefore, the study recommended making marketing images reflect more diverse demographics.

“When asked who the typical wine drinker is, 35% of Hispanics, 34% of Asians and 27% of Blacks said they were of a different culture than them versus only 13% of non-Hispicanic Whites,” the study authors wrote. “Marketing portrayals of wine drinkers must become more inclusive to attract new consumers.”

Wine Pigeonholed for Formal Occasions and Gift Giving
Wine positioning should be more about fun and less about formal, the study found, with respondents saying they associated wine with a high-end restaurant meal (59%) or as a good choice at an Italian restaurant.

Only 10% said a concert or sport event was a good wine occasion.

While their ideal retail price point while shopping off-premise remains $10 to $20, the data showed this group often prefers small cans or bag in box wines, allowing retailers better price flexibility in meeting the $10 to $20 purchase price.

Relatable Wine Marketing
Counteracting that formal occasion mindset, Lakusta pointed out the wine shop Pairings Portland, run by retailer Jeff Weissler, has made wine tastings very relatable, hosting shop tastings focused on Taylor Swift’s Eras tour, Harry Potter, Dune, Lord of the Rings, Pride and Prejudice, Tarot for 2025, Disney Princesses and more.

The study also showed 61% of those studied preferred sustainable, family-owned brands, with 58% explicitly preferring organic (80% of the wines offered at Weissler’s shop are organically farmed.)

Paint and sip events were also popular at other venues.

A recent study by Wine Market Council, “Attracting More Young Adults and Multicultural Consumers to Wine,” found wine positioning should be more about fun and less about formal, with respondents saying they associated wine with a high-end restaurant meal (59%) or as a good choice at an Italian restaurant (courtesy Wine Market Council.)

Better Wine Descriptions and More Wine Cocktails
In the on-premise world, the study found a startling contrast between the way regular cocktails were marketed on menus, with appealing descriptions of their flavors and ingredients, while wine by the glass had little to no descriptions on menus.

“Wine marketers must demand better wine menus, lists and choices at on-premise,” the study authors wrote. “All groups indicate they wish there were more wine choices at on-premise and there was more information about the wines they can choose. Lack of descriptions and taste information make wine less appealing.”

The study also found wine cocktails were a hot, on-prem opportunity with 72% of 20- and 30-somethings saying they would be likely to purchase wine in that form.

Roughly 30% to 40% of them were aware of wine slushies, frose, wine cocktails mixed with spirits, wine spritzers and wine aperitif cocktails (with Aperol, Campari, etc.).

The Infamous Wall of Wine: It Only Gets Worse Online
Echoing previous studies, the wall of wine in retail continues to be an obstacle for most consumers, with 25% to 30% saying they are overwhelmed. They say wine aisles should be “better organized.” Most reported buying by a brand they know (as a way to combat the overwhelm).

Online, they tend to buy wine at a grocery store’s site (44%) or liquor/wine brick and mortar store’s site (42%). 33% buy from a strictly online retailer (e.g., wine.com) and 28% buy online from a winery.

When shopping online, they pay most attention to peer reviews (39%), similar to their shopping habits for other types of purchases.

20% say wine shopping online is harder to navigate than in a store.

Echoing previous studies, the wall of wine in retail continues to be an obstacle for most consumers, with 25% to 30% saying they are overwhelmed.

Wine Additives Give Them Headaches
An unusual finding: Between 15% and 20% of respondents said wine gives them headaches, leading the study’s authors to write, “Marketing methods utilized to minimize this could have an effect on up to 20% of consumers.”

Dry whites (Sauvignon Blanc or Pinot Grigio) and sparkling wines all have lower histamine levels compared to red wines.

Light at the End of the Tunnel: Millennials
While earlier reports have blamed wine’s slower sales on younger drinkers, Lakusta did not embrace that point of view. “There’s a very good light at the end of the tunnel, particularly with millennials when they hit their 30s,” he said.

The full webinar and data are available to Wine Market Council members. Membership information is available on their website at winemarketcouncil.com/join.

‘YES’ Vote Urged for Referendum to Continue Pierce’s Disease Control Program in California

By
Natalie Collins | President, California Association of Winegrape Growers
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Xylella fastidiosa, the bacterium responsible for Pierce's disease, poses a significant threat to vineyards, highlighting the importance of ongoing pest control efforts.

The Pierce’s Disease Control Program within the California Department of Food and Agriculture (CDFA) has been slowing the spread of the glassy-winged sharpshooter (GWSS) and minimizing the impact of Pierce’s disease (PD) in California vineyards for over two decades. The program is overseen by the PD/GWSS Board and is made up of industry leaders, including growers and wineries alike.

The core strategies of the program are to protect California winegrapes through the following means:

• Contain the Spread: Prevent the spread of GWSS to non-infested areas with nursery inspections, trapping, treatment, bulk citrus inspections, area-wide treatment programs and biological control.
• Statewide Survey and Detection: Find new GWSS infestations and confirm that non-infested, at-risk areas remain free of infestation.
• Rapid Response: Respond quickly to detections of GWSS in new areas with surveying and treatments.
• Outreach: Raise awareness about PD and its vectors.
• Research: Sponsor research and development for sustainable solutions to PD and its vectors.

California winegrape growers are urged to unite and support the referendum for the continuation of the Pierce’s Disease Control Program, ensuring the protection of vineyards against invasive pests (all photos courtesy California Association of Winegrape Growers.)

By design, the program is subject to a referendum of growers once every five years. This referendum is to hold the program accountable and to make sure growers are satisfied with the work the program is doing on their behalf to protect vineyards. Therefore, the California Association of Winegrape Growers (CAWG) co-sponsored legislation in 2024 to create the referendum in spring 2025. 

Last year, when Assemblywoman Dawn Addis authored AB 1861 to extend this crucial line of defense for the wine industry against an invasive disease, she said, “We have a track record of collaboration among State, local, federal government and the industry itself when it comes to battling Pierce’s disease and the glassy-winged sharpshooter. I’m proud to extend this collaboration and to be part of the on-going success of California’s wine regions.”

AB 1861 was approved unanimously by the legislature in 2024 and was signed into law by Governor Newsom. This means CDFA will conduct a vote of growers this spring to determine whether the program and the PD/GWSS Board will be extended from 2026 to 2031. The last PD/GWSS referendum, conducted in 2020, passed with 78% approval of California winegrape growers. CAWG urges a ‘YES’ vote this spring to continue the program.

Continuing to Address PD/GWSS
Growers know all too well one of the most pervasive pests to vineyards is the aggressive PD, carried between plants by GWSS. PD is caused by the bacterium Xylella fastidiosa. Since the 1990s, GWSS has been one of the most invasive and deadly pests for vineyards. When a vine develops PD, its ability to draw in moisture is hindered, and the plant will either die or become unproductive. PD has caused millions of dollars in damage throughout the state.

Xylella fastidiosa works by blocking the xylem in plants, which conducts water around the plant. Symptoms include chlorosis and scorching of leaves. Entire vines will die within one to five years. GWSS, Homalodisca vitripennis (formerly H. coagulata), is a far-flying leafhopper, which means it can easily spread the disease-causing bacterium from one plant to another. When GWSS feeds on a plant infected with Xylella fastidiosa, it acquires the bacterium and transfers it to another plant when it feeds.

Over the last 23 years, the program has been fundamental in addressing the challenges posed by PD and other pests and diseases. In the last two years alone, there was a Notice of Treatment and Proclamation of an Emergency Program in Fresno, Madera, Solano, Stanislaus and Tulare counties to knock down populations of GWSS.

California’s first indication of a severe threat posed by this disease occurred in Temecula in August 1999, when more than 300 acres of vineyards were infected with PD and had to be destroyed. In response, the Legislature enacted a legislative package that year, creating the advisory task force. In 2001, the program was created to fight the spread and find solutions for PD and GWSS.

The PD/GWSS Board has invested $55 million in research to combat pests and diseases threatening California’s wine industry.

Program Has Solid Track Record
The program, funded through a combination of federal and industry funds as well as grape grower assessments, has demonstrated success in controlling the spread of PD and GWSS. These assessment funds are used for research, outreach and related activities on PD, GWSS and other designated pests and diseases of winegrapes.

The research overseen by the PD/GWSS Board is critical to advancing knowledge, improving practices, and guaranteeing the longevity of the California winegrape industry. The focus of current research projects ranges from investigating pests and diseases to evaluating existing control methods to exploring new promising control strategies.

Since 2001, the PD/GWSS Board has invested $55 million to support about 300 research grants to protect vineyards, prevent the spread of pests and diseases, and deliver practical and sustainable solutions. Research is focused on PD and GWSS, and other designated pests and diseases of winegrapes, including:

• Brown marmorated stink bug
• European grapevine moth
• Grapevine fanleaf disease
• Grapevine leafroll disease
• Grapevine red blotch disease
• Mealybugs
• Spotted lanternfly (SLF)

The PD/GWSS Board is looking ahead regarding SLF. Native to Asia, SLF started showing up about 10 years ago in eastern states and has caused substantial damage to vineyards in Pennsylvania, New York and the region. Education is crucial to early detection and treatment as the pest continues to make its way west. Investing in research now will also aid in identifying a means of quick treatment and eradication of the pest when it does make its way to California.

For all the aforementioned reasons, in support of growers, CAWG is urging the passage of the referendum in 2025.

“Know More, Use Less” New Precision Imaging Vineyard Software Enables Smarter Use of Inputs

By
Pam Strayer | Contributing Writer
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Precision imaging vineyard software, which can recognize underperforming vines in a vineyard among other insights, can now be mounted to ATVs and cover larger areas significantly faster than a human on foot (photo courtesy Bloomfield AI.)

What if you could target underperforming vines in a vineyard and apply more resources to them, not to entire blocks? What if you could improve yield estimate accuracy so you would know whether you’re a grape buyer or a seller this year? What if you no longer had to send workers into fields to scout vines, but could collect useful data during the passes you already make and, afterward, view actual scans of the fruit for all your vines?

Experts making new precision imaging vineyard software say these are attainable goals, and several of California’s biggest vineyard companies are piloting their products. Vendors are on the cusp of rolling out these next-generation labor saving products more broadly to large-scale growers in 2025.

While most vineyard managers today rely on aerial imaging from flyovers from VineView or Ceres AI (which covers 350,000 acres of vines globally flying at an average height of 3,500 feet), vineyard managers large and small are taking a real-world look at what next-gen precision imaging vendors like Green Atlas, Bloomfield AI and Scout AI offer. These new products provide insights from photos taken in the vine row.

“Imaging tech is really blowing up,” as one North Coast vineyard manager put it. Part of the reason? Future proofing. These new precision tools are poised to enable variable-rate spraying products major hardware vendors are currently developing.

Scout AI user interface via mobile app. Developed and funded by California-based data scientists and investors, Scout AI is focused solely on winegrape vineyards. It uses only cameras on ordinary Samsung phones to assess vine and grape quality, a design choice CTO Mason Earles insisted on early on (photo courtesy Scout AI.)

Three Precision Imaging Systems: Green Atlas, Bloomfield AI and Scout AI
Two of the early entrants, Green Atlas and Bloomfield AI, cover multiple crops and use proprietary cameras, while one, Scout AI, is focused solely on vineyards and uses ordinary Samsung phone cameras.

Green Atlas, Treasury Wine Estates trial
At Treasury Wine Estates, viticulturist Allie Hermanson has been trialing Green Atlas on 120 acres for several years. Green Atlas is an Australian-based company that has historically trained its data collection and insights on orchard crops.

“We did actually see quite a difference between our manual counts and the Green Atlas counts, which we thought was interesting, because they’re collecting so much more data than ours,” said Hermanson.

Bloomfield AI, Gloria Ferrer
Pittsburgh-based Bloomfield AI, recently acquired by Kubota, was used in 2023 at Gloria Ferrer in Sonoma, Calif., according to Bloomfield’s website. Quoted in the press, vineyard manager Brad Kurtz said, “Yield monitoring is just the very tip of the spear of what this technology is going to bring to agriculture.”

Scout AI, various vineyards (Mayacamas, Hardin, Enterprise and others)
Developed and funded by California-based data scientists and investors, Scout AI is focused solely on winegrape vineyards. It uses only cameras on ordinary Samsung phones to assess vine and grape quality, a design choice CTO Mason Earles insisted on early on.

Like an X-ray, Scout AI’s software shows where red blotch is suspected and lets growers view photos of any individual vines. This differs from traditional satellite imaging used in the winegrape industry by many vineyard managers in California (photo courtesy Scout AI.)

Earles is a UC Davis viticulture and enology assistant professor who runs the Plant AI and Biophysics Lab (the university owns a tiny percentage of Scout.) The main investor is Silicon Valley entrepreneur-turned-vintner Kia Behnia, a wine industry innovator who was already a data geek in his previous career and in his life as a vintner in Napa starting a decade ago.

After successfully beta testing for two years with boutique, artisanal growers in Napa and Sonoma and with two of California’s largest wineries (among the top six in the state), Scout released its fourth-generation version software in December based on three years of vineyard research with growers in both low-priced and high-priced winegrape regions.

Matt Hardin, owner of Hardin Vineyard Management, has been using it with his team and finds it increases efficiency and saves labor.

Said Hardin, “At the end of the year on every single ranch, I used to send a guy through to look for missing vines, rootstocks, young vines, etc. With Scout, we were able to do a scan with one guy. The software would count not only all our missing vines, and all our rootstocks, it would also export all that data which we send to the nursery to order plants. It takes only one guy four hours on a four-wheeler instead of four or more days. And all the data comes back to us.”

After doing a vine inventory with Scout, Steltzner Vineyards in Napa’s Stag’s Leap District found out of 24 acres of vines, it had a half-acre of missing vines. For fifth-generation Napa grower Allison Steltzner, the first scan paid for itself already.

Behnia said these savings are typical across its many users.

“We can do this scouting now on an ATV at 9 miles an hour, about five times faster than it would take humans walking around with a clipboard or with a clicker,” he said.

“The first thing we did for all our customers,” Behnia continued, “is to do an inventory so they have accurate baseline data. The second thing is identifying the lowest-performing vines in every block. Fixing those will get you back into profitability a lot more than focusing on the top ones, right?

“Most people don’t know where those are,” he said. “We literally get down to creating a watch list. Now, some of our customers are doing targeted treatments like compost or biochar just for those vines. Their plan is to see if those vines don’t improve after two years, then maybe they have to replant because the plant was damaged or is not worth keeping.”

Like an X-ray, Scout’s software shows where red blotch is suspected and lets growers view photos of any individual vines.

Hardin said having the data Scout collects is a conversation enabler with customers. “It’s a tool I can use to talk with my clients,” he said.

After meetings in 2024 with 20 growers in Paso Robles and others in Monterey, in 2025, the Scout team is expanding their product offering to more regions and growers, including many large-scale growers with 5,000- to 10,000-acre vineyards.

“We believe we have the largest ground set of photos anywhere in the world,” said Behnia. “What this does, and I think this is where our customers get excited, is not only does this help them this year, but five years from now, they can go back and look at the data.”

Adoption
It’s still early days for the precision imaging industry, and many vineyard managers are waiting on the sidelines for others to prove that the data provides return on investment. But most believe the day is coming when these tools will be the industry standard, widely used in all vineyards.

“When I show it to winemakers, they say, ‘I asked Google to build this 10 years ago. For a lot of them, they’re just in awe,” said Behnia. “The idea is so simple. It’s just they couldn’t believe that we can finally do this now.”

Said Earles, “I think Scout is a tool in your tool belt that can help you farm more profitably and far more sustainably through precision agriculture.”

Added Behnia, “We’re building a tool that helps you measure. If I can measure what you did, that will change culture. I’ve seen this before. Over half my career was built on creating business tools that changed cultures and organizations so that they become data-driven and measure the right things.

“Given climate change and labor shortages, no one can continue doing the same thing they’ve been doing in the next five years,” he continued. “Labor is not going to get cheaper. Oil industry-generated inputs are only going to increase in cost. Today, growers too often spray everything, and agrochemical and farm input companies get a big check. We all need more targeted inputs. We can’t go backward.”

Ground Truth Data on Regenerative Practices: Insights from Real-Time Soil Monitoring

By
Pam Strayer | Contributing Writer
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Agrology’s Arbiter soil monitoring system measures soil microbial biomass and continuous metabolic activity in the soil, which provide advantages compared to more static measurement systems disadvantaged by lag time from sending samples to a lab and waiting for a result.

What are the impacts of various vineyard practices on soil health, water retention, soil temperature and yields? Agrology, a soil health monitoring vendor, provided data and insights in a year’s-end online webinar showcasing data from more than a half dozen vineyard clients it works with in California.

Agrology’s Arbiter soil monitoring system measures soil microbial biomass and continuous metabolic activity in the soil, which provide advantages compared to more static measurement systems disadvantaged by lag time from sending samples to a lab and waiting for a result. Static sampling does not provide real-time data on fluctuations.

“The Arbiter system looks at CO2 concentration in three different ways,” said Charlie Dubbe, head of regenerative partnerships for the Sonoma-based company. “It looks at it through a soil chamber, looking at what’s called soil respiration.

“We’re telling you what the actual activity is based on the real-world conditions of soil moisture and the climate that you’re in and the practices that you’re doing. So, it’s this really interesting continuous measurement of the amount of life in your soil.

“The larger and more robust that dialog is between soil microbiome and plant roots, the better a plant can produce these biochemicals that are called secondary plant metabolites,” he said. In wine, those are polyphenol compounds and tannins.

Dubbe said up to 50% of the energy that plants gather from the sun is released into the soil microbiome then slowly processed by the soil microbiome and humified (turned into humus). “That stable carbon form is what we’re really looking forward for,” he said, both for fighting climate change and increasing crop production.

“So, long story short, Agrology monitors that amount of microbial activity through soil respiration,” Dubbe said.

The trio of presenters then went on to provide a cornucopia of data from various clients and vineyard sites, ranging from Napa and Sonoma to the Central Coast, looking at no-till practices. Data showed no till preserved soil structure, enhanced microbial life and water retention and reduced the need for irrigation. It also improved overall soil health.

“No-till methods, while potentially more labor-intensive and difficult to implement to transition, offer longer-term benefits like improved water retention, reduced evaporation and better microbial health,” said Dana Revallo, Agrology’s head of customer success.

“We know consistent tillage does very bad things for the soil microbiome,” added Dubbe. “No. 1, by just disrupting all their homes and kind of slicing up the structure and destroying that pore space, you’re creating this massive feast, you’re chopping up all the soil organic matter, and then you are adding all this oxygen, so there’s this massive kind of burst of activity. But all that food is gone later in the season.”

“The Goldilocks Zone”: No Till’s Benefits in Soil Temperature and Moisture
Jay Radochia, head of agribusiness development at Agrology, pointed out soil temperature plays a critical role in determining the rate of evaporation and microbial activity in the soil.

“When the top 6 to 8 inches of soil goes above 100 degrees [F], we lose 85% of that moisture just through evaporation,” he said. “The full-till blocks experience soil temperatures over 100 degrees [F] for extended periods. By contrast, the no-till practices buffered soil temperature fluctuations, keeping temperatures lower and stable. The data from the trial showed the full till resulted in 69 days, or exceeded 85 degrees [F], while the no till above 85 was only 29 days.”

When the top 6 to 8 inches of soil goes above 100 degrees F, 85% of moisture is lost just through evaporation, Agrology’s Jay Radochia says.

Water Retention
The team also reported no-till practices yielded the highest water retention levels, allowing the soil moisture to be more effectively held, rather than full till or the every-other-row till. The ability to reduce irrigation while maintaining healthy soil is a significant advantage, they noted.

The full webinar with several case studies, including some from Donum Estate, Joseph Phelps and a very large grower, provides graphs and insights into a variety of practices, including using rye as a cover crop, ROI analyses and more. It can be seen online at https://www.youtube.com/watch?v=yvfUipcXJzQ.

Can Regenerative Organic Farming Pencil Out? Study Provides State-of-the-Art Data and Demonstrates Dramatic Improvements in Wine Quality

By
Pam Strayer| Contributing Writer
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Robert Hall Winery General Manager Caine Thompson came on board in 2020 and got the thumbs-up from O’Neill Vintners & Distillers CEO Jeff O’Neill to start the regenerative organic trials.

At Robert Hall Winery on Paso Robles’ east side, a remarkable three-year study is comparing yields, costs, wine quality and more in a conventionally farmed vineyard and a regenerative organic one (supplemented with biodynamic herbal and mineral sprays and compost). The results show a dramatic difference in water retention, soil respiration, soil carbon, wine quality and yields.

The regenerative organic certification (ROC) requires organic certification enhanced with additional practices, including no till, animal integration and keeping the ground covered. The standards were created and are enforced by the Regenerative Organic Alliance (ROA).

Usually, winery trials like this take place under cover of darkness and are typically aided only by subjective, qualitative assessments. Often, growers will try out organic farming on a block or two (and the same for biodynamics) and decide whether to implement these farming techniques. After several years of building their confidence through various vintages, they may decide to become certified organic.

Not so at Robert Hall, which has jumped into an impressive research study that is finding startling new results and is open to the public and peers thanks to an initiative proposed by General Manager Caine Thompson. The winery is also on the brink of ROA certification, having met all the requirements and awaiting the final paperwork.

Thompson praised the ROA certification not only for its faming standards but for the human social fairness practices it encourages. “We’ve got a really transparent feedback loop with monthly meetings with the vineyard team and myself and the winemaking team,” he said. “We’ve noticed more engagement, and turnover has gone down. The quality of work has gone way up.”

When Thompson came on board in 2020, he asked Jeff O’Neill, CEO of O’Neill Vintners & Distillers, if he could conduct a side-by-side comparison and measurement of conventional versus regenerative organic (no till and more). Tablas Creek, certified both biodynamic and ROC, had previously worked with academics to study the impacts of tillage and grazing, which provided a helpful precedent. O’Neill gave the Robert Hall study the thumbs-up.

Thompson, a native of New Zealand, had personally been farming organically and biodynamically for 20 years in New Zealand at Pyramid Valley and Mission Estate Winery and had previously conducted research on converting to organic.

Begun in 2021, the Robert Hall study encompassed 48 acres in the vineyard surrounding the winery (in the Geneseo AVA). 43 acres were converted to regenerative organic. 5 acres were retained as the conventional control. The control includes the use of cover crops and compost which advantaged it with better practices than the average conventional vineyard (though cover crops are widely used). Both the control and regenerative organic vines are Cabernet Sauvignon (clone 15, originally from the Bordeaux region).

Thompson wanted to make sure he was measuring like with like and went the extra mile to make sure that was the case. “We had satellite images and soil maps to ensure we were setting up the trial with like for like literally side by side, the same soil type and the same clone,” he said.

Four years later, he and his team have a lot of data to look at and experiences to review.

Their ongoing study is finding regenerative organic practices have benefits that exceeded their expectations. “I was surprised at how quickly the differences showed up,” he said. “Even in year one, there were noticeable changes.”

On a vineyard tour in November, he pointed to a newly planted neighbor’s vineyard, where the soils were clearly pure hardpan.

“When we broke ground farming this way four years ago, you could barely get a spade into the ground,” he said. “Now, we’ve got a living, breathing soil.

“The soils are more open, more friable, and there’s just so much more life within the vineyard. When you walk into the vineyard now, it’s like this biodiversity nightclub of energy and insects and life all around you, and I think that’s translocating down through the roots, into the soil, and you’re getting that expression back up into the fruit and then into the resulting wine,” he said.

Regenerative organic farming is easier in addition to being more rewarding financially, he said.

“When you have that type of biodiversity within a vineyard, the diversity and the predators take care of a lot of the pests and disease. You’re building these polycultural systems; it’s not just a monoculture. You’ve got a whole bunch of different cover crops growing in there and different species. You get more diversity through predators in there, so the pest populations get brought into balance naturally,” he added.

“When we started the project, we were doing three to four biodiversity drops of pest predators to build up a baseline [predator] population. Now we’re only doing one or two. They’re basically maintenance drops now, and of course, there’s no insecticides being used, no herbicides being used, no synthetic fungicides.”

The team has the data to prove yields are up, water retention is up and wine quality is improving, he said. In 2021 and 2022, they collected all the data themselves.

Farming costs for the regenerative organic block increased an average of 10% annually overall.

Agrology Technology Adds Insights: Water Retention Up 13%
In 2023, the study began integrating state of the art carbon monitoring and other data-gathering technology from Agrology, measuring soil moisture, soil respiration, CO2 in the canopy, carbon concentrations in soil, and ground and canopy temperatures.

The team found the regenerative organic block increased water retention 13% in just one year compared to the conventional block. In a region that typically gets only 18 inches of rain per year, while the climate continues to warm, that is significant.

The regenerative organic vines also boosted microbial activity, Agrology found.

Regenerative Organic Mitigated Heat and Heat Spikes
This fall, Paso’s heat spikes shattered heat records for six days in a row, reaching a high of 107 degrees F and affecting soil temperatures.

The regenerative organic block were consistently lower in temperature than the conventional block, the data showed. Similar results applied in measuring the canopy temperature.

The team calculated there was “a 7.8% decrease in average daily high temperature during the critical harvest period in the regenerative block,” when grapes are typically in danger of ripening too quickly.

Carbon Sequestration Bolstered
In October 2023, the accumulated canopy absorption of CO2 was 26.79 PPM in the control block versus 1,397 PPM in the regenerative block, leading the study to conclude the regenerative block absorbed 192% more CO2 than the control. Organic carbon in the regenerative block was 1.51% vs 0.86% in the conventional block as of July 2024.

The regenerative block scored 7.8 on the Haney soil health score compared to 4.7 for the conventional block.

Yields and Costs
Yields were up three out of four years in the trial, while farming costs increased an average of 10% annually overall, Thompson said.

In the trial’s fourth year (the 2024 vintage) during another warm vintage, yield data showed a 15% increase in the regenerative organic vines.

The conventional control yielded 1.85 t/acre while the regenerative organic yielded 2.17 t/acre. The data highlights in three out of four years, the regenerative organic vineyard has produced a more resilient canopy that has helped protect the fruit, leading to improvements in yield.

Canopy comparison of regenerative organic and conventional vines during year two (summer 2022) of the trial.

Wine Quality Skyrocketed
Another major benefit was dramatically increased wine quality.

Thompson and winemaking partner Amanda Gortermade made wines the exact same way from both the conventional block and the regenerative organic block. After seeing dramatic improvement in wine quality, they upgraded cultural practices in specific areas within the regenerative organic vineyard, increasing shoot and crop thinning in the hopes of creating a $50 bottle wine. Mission accomplished.

“There’s more complexity in the wine compared to the conventional control,” Thompson said. “There’s freshness, there’s more vibrancy, there’s a different energy in the wines. We’ve got more of those classic Cabernet characters,” he said.

Yields in the trial were higher three out of four years for the regenerative organic block vs the conventional block.

Sharing the Data (and the Wine)
An advocate for regenerative organic farming, Thompson is enthusiastic about sharing the trial’s data and findings with the world.

“The whole idea of the study was to be collaborative, to be open to industry,” he said. “We hold quarterly field days to share the results and the learnings and this whole journey toward regenerative organic.”

Visitors are welcome to taste the wines side by side from the trial during field days (open to all) to compare the differences for themselves.

Thompson’s scope in applying learnings from the study is wider than the vines at Robert Hall. He oversees sustainability for all O’Neill Vintners & Distillers properties (the seventh-largest winery in California) and sits on the boards of several international sustainability groups.

O’Neill’s vast holdings include 870 acres in Parlier, Calif. The company also contracts 200 growers with 15,000 acres of vines. All are now required to meet some kind of sustainability program requirements. In July, O’Neill purchased its first Washington winery, Wines of Substance. O’Neill’s luxury brand, Ram’s Gate in Sonoma, is in the process of becoming certified regenerative organic on 28 acres in the Carneros AVA.

Thompson’s study has reinforced his belief and experience that regenerative organic winegrape growing can be profitable for all.

“We now have a vineyard that’s alive, that’s diverse, and more resilient in the face of climate related issues and pests and disease,” he said.

“The vineyards are definitely becoming more resilient to climate change and some of the extremes that we’re seeing with temperature, with heat, and the pressure that’s put on canopies and fruit. Under the regenerative organic side, we’ve got a bigger, healthier canopy, resulting in more shade and protection. We’ve got darker, greener leaves that are working really efficiently, and they’re protecting the fruit. Those leaves obviously move with the sun, but they protect the fruit in these larger canopies, so the resulting fruit is intact. It’s not shriveled, it’s not dehydrated, and that’s leading to better wine quality,” Thompson added.

Robert Hall Winery offers consumer and trade vineyard tours to the control and regenerative organic blocks (side by side) and schedules field days that provide growers and others to learn in depth about the trial.

The full study can be seen online at shorturl.at/suO86.

Blending Wine and Philanthropy at Rancho Oso Libre: The Social Impact of Sustainable Wine

By
WHITNEY BROWNIE | Vineyard Team
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The Oso Libre Por Vida Foundation, an integral part of Rancho Oso Libre dedicated to helping those in need, predates the winery by nearly two decades.

Today, Paso Robles residents Chris and Linda Behr may be best known for their successful cattle ranch, winery and SIP Certified® sustainable vineyard: Rancho Oso Libre.

Anyone who has visited the ranch and talked with the Behrs probably knows about their dedication to helping those in need through their Oso Libre Por Vida Foundation. But they may not know the origins of the Foundation predate the establishment of the winery by nearly two decades.

Before the Behrs moved to Paso Robles and started the ranch, they lived in Los Angeles. At this time, Chris ran his construction company, Behr Construction.

Chris was contracted by the Children’s Institute to build special one-way interview rooms to give children a safe space to share their stories. The rooms would allow a social worker to work with a child privately while another agent could observe the interaction without being intrusive or putting stress on the child.

For Chris, this experience turned into more than a construction project. The job invited him to learn about the Institute’s mission. He saw children heal through dedicated time and support, and it moved him deeply.

This experience inspired Chris to reach out to the Big Brothers Big Sisters of America program. He felt called to become a mentor. During his time with the program, he took on challenging cases and even coached others to become a “Big” mentor.

Helping children was just the beginning of his and Linda’s devotion to charitable practices. Their attention next turned to people involved with the armed forces, and then to animals in need. When Linda’s parents were diagnosed with and eventually passed from cancer, they dedicated funds to support cancer research.

The impact of Chris’s work with children in need and Linda’s parents’ illnesses were instrumental to what several years later became the Oso Libre Por Vida Foundation.

Chris and Linda Behr are owners of cattle ranch, winery and SIP Certified® sustainable vineyard Rancho Oso Libre (all photos courtesy Rancho Oso Libre.)

La Vida En el Rancho
In 1996, the Behr’s hearts called them north. They bought a 90-acre ranch on the west side of Paso Robles to pursue farming.

The birth of Rancho Oso Libre was a group effort. Chris drew up plans for the home and winery. His Behr Construction crew brought the plans to life. Over the next four years, the Behrs planted their grapes and acquired cattle. In 2000, their good friend Michael Barreto taught them how to make wine.

In 2008, Chris and Linda’s son, Jeff, and his wife, Liz, joined their parents to put the finishing touches on the winery. But Jeff and Liz’s visit yielded more than a winery ready for business.

The group discussed how the Behrs would tie their charitable services to the winery. Chris and Linda wanted their passion projects to be intertwined, but they weren’t sure what that would look like.

That’s when Linda came up with the name “Oso Libre Por Vida” Foundation. Together with the name of the ranch, the translation is “Free Bear for Life.” The name ties the two together in a meaningful play on the Behr’s name and their charitable philosophy.

Although still unsure of what the union would look like in practice, Chris and Linda knew with a great name and a winery to engage the community, they were off to a good start.

Votive Candle Offering
One of the first features that entwined Rancho Oso Libre and the Por Vida Foundation was built into the winery itself, or, rather, omitted from it. Chris left a hole in the wall near the winery’s entrance.

Despite uncertainty over how the feature would be accepted, the Behrs left this opening for a Votive candle offering: A space for their guests to take a moment to think about someone they love and light a candle in their honor.

To their surprise, it was a hit. The Behrs found that as well as lighting candles, guests were leaving offerings at the Votive. “We really didn’t think it would be used,” Chris said. “Early on, a woman came up to me to tell me the tray was full and handed me her offering. That’s when we knew this was something people truly appreciated.”

All Votive offerings are donated to support people and animals in need under the Por Vida Foundation. At the end of each weekend, Oso Libre’s team collects the offerings from the tray and puts out fresh candles for the following week’s guests.

Winemaker Michael Barreto is a business partner in Rancho Oso Libre and taught the Behrs how to make wine.

Vines, Wines and Angus
With the space to host, wine to bring people together and beef to feed them, the Behrs came up with another way to tie the ranch’s activities to the Por Vida Foundation: Saturday Angus Days.

While tickets to the event welcome guests to enjoy an Estate Angus Burger, sides, wine and live music, they also give back to the community.

Each of Oso Libre’s Angus Day events is held to support a specific cause. Prior to each event, the team sits down to decide what that cause will be. If there is an issue or tragedy affecting the community, that’s where their Angus Day proceeds go.

Chris said Angus Days have “really gotten a life of their own. People connect drinking their wine with the money that will go to charitable causes; some even give money without drinking wine.”

The Behrs host around 20 Angus Day events each year, inviting the community to come together to enjoy great wine and angus and support those in need. “If people don’t like their burger, they like it more knowing it goes to charity. They say, ‘That burger was delicious.’”

Poker-Style Tasting Chips
Oso Libre’s Poker Style Tasting Chips are tasting certificates with a twist. Similar to standard certificates, guests can exchange a chip for a complimentary tasting for two. What makes them unique is for each chip that is redeemed, Oso Libre gives $5 to charity.

Chips are easy to come by. They are given to new members who can pass them along to friends, and Oso Libre staff hands them out to guests at their own discretion.

The over-1000 chips Oso Libre distributes each year represent thousands of dollars the community helps give in charitable contributions.

Rancho Oso Libre has a tradition whereby all its wines are combined into one called Solera. It’s served growler-style in the tasting room.

Solera
The beacon of the winery is the Solera wine program. “It’s a continuous layered wine that has over 10 years of vintages and varietals,” Chris said. “Every wine we make is in it.”

Solera is treated like a growler at a brewery. Oso Libre even uses growler bottles for this special club-exclusive blend. Two barrels of Solera are kept safe right in the tasting room so members can bring their growler in and watch it be refilled. All proceeds from Solera sales and refills go to the Por Vida Foundation.

The Solera tradition began in 2004, back when Jeff and Liz were Oso Libre’s winemakers. Since then, Solera has never been emptied.

“We keep the bung proper, keep nitrogen clear, monitor S.O., we keep it safe and freshen it up. It’s got to taste great, people love it,” Chris said.

When Jeff and Liz returned to Los Angeles in 2019, the Behrs brought in winemakers Michael and Joey Barreto, who are now also business partners. The team who taught the team how to make wine in 2000 continue the Solera tradition today.

Every quarter, the Oso Libre team counts all the Por Vida Foundation funds and sits down to decide how they will be distributed to different charities.

Passion in Every Pour
Every quarter, the Oso Libre team counts all the Por Vida funds and sits down to decide how they will be distributed.

Keeping with the roots of their charitable activities, Chris and Linda donate most of the funds to the same four main causes: cancer research, prevention of child abuse, support for armed forces and veterans, and humane care of animals.

“We often plan weeks or even months in advance,” Chris said. But tragedy can strike at any time. If the team hears about an issue affecting the community, plans change and they direct funds toward reliving the local issue.

“We’ll switch gears if a big deal comes up and dedicate an event to it.”

Chris and Linda Behr take great pride in Oso Libre’s Por Vida Foundation and love telling their guests how their visit supports the community. “People connect enjoying wine with giving back,” Chris said. “It makes them feel pretty darn good!”

Sustainability doesn’t stop at the farm level. Like Oso Libre’s Por Vida Foundation demonstrates, it includes socially responsible practices that support the community and those in need. A winery in San Luis Obispo, Calif. found a creative way to get their staff involved in finding new ways to practice sustainability. Read the next Sustainable Story to learn how.

California Association of Winegrape Growers Begins Work on 2025 Advocacy Agenda

By
Steve Pastis | Contributing Writer
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Senate Bill 399, which addressed employer intimidation at a heightened level, was top of mind for California Association of Winegrape Growers during the 2023-24 legislative session (photo courtesy Kingman Ag.)

The California Association of Winegrape Growers (CAWG) prides itself on its work advocating for (or when necessary, against) legislation that affects the winegrape industry.

“One of the most essential and valuable CAWG member benefits is advocacy,” states the organization’s website. “CAWG is the only statewide organization dedicated exclusively to protecting and promoting your interests before the state legislature, Congress and regulators.”

Now that the 2023-24 California legislative session is over, Michael Miiller, CAWG’s director of government relations, looked back at the most important bills of that session and looked ahead to the group’s advocacy goals for 2025.

Senate Bill 399
Earlier this year, CAWG urged a “no” vote  on SB 399 in the California State Senate. This was arguably the most important of the more than 20 bills that CAWG took a stand on.

“The bill was sponsored by labor unions, and they said the bill was needed to make sure employers aren’t forcing their employees to listen to political posturing, diatribe, whatever, from their employer,” Miiller explained. “That’s what they said the bill is trying to do.

“But that is already illegal,” he said. “I can’t say, ‘Hey everybody, stop what you’re doing and let’s get together and talk about whatever candidate.’ That’s not allowed in the workplace. You can’t push your employees to do that.

“But the bill, the way it was written, goes way, way, way beyond that,” he continued. “It basically says things like if you have a vineyard and you put up a sign that says, ‘Vote for Bob for State Senate’ and any employee who’s working in that vineyard doesn’t like Bob, they can say, ‘I refuse to work at that vineyard because I don’t like Bob, and I don’t want to see that sign.’”

Despite CAWG’s efforts, SB 399, known as the California Worker Freedom from Employer Intimidation Act, was signed into law in late September and will take effect Jan. 1, 2025.

California Association of Winegrape Growers is looking to revisit the housing issue for ag workers in 2025. Director of Government Relations Michael Miiller said the first step toward more affordable housing for ag workers would be streamlining the permitting process.

Groundwater Recharge
The organization was more successful with groundwater recharge legislation and is currently considering ways to expand it in 2025.

“Even though we have droughts, and climate change is real, we know how climate change is going to affect the water supply,” Miiller said. “We’re still going to get the same amount of water, but it’s going to be delivered differently.

“We’re not going to get the big snow cap in the Sierra that we’ve had before,” he continued. “We’re not going to get a routine winter rainfall like we have before. Instead we’re going to get periods of drought and we’re going to get periods of heavy storms.

“So, what we what we’ve done is to say, ‘Well, we have the heavy storms happening right now, and that water is in large part flowing out to the Pacific through flood protection and storm water runoff in urban settings,’” Miiller said. “What we’d like to do is capture that water and pump it underground and do groundwater recharge so we have a more reliable supply of groundwater across the state.”

Miiller believes local groundwater basins with a Sustainable Groundwater Management Act (SGMA) program in place should receive some kind of a credit.

“If you are actually pumping water underground, adding to the groundwater supply, shouldn’t there be a little bit of a break for you?” he asked. “The discussion of SGMA has to be not just on the demand side but on the supply side as well.

“We need to make it easier for people to do groundwater recharge because that is the future of our water supply in California,” Miiller said. “We really need to make that a priority.”

He suggested the possibility of a metering system to determine credits like how credits are calculated for electricity generated by solar energy.

“We’re still looking at the concept,” Miiller said. “We’re working with environmental groups. We’re working with water agencies and others to figure out how we want to approach that next year.”

The California Water Supply Solutions Act of 2023 was authored by Senator Angelique V. Ashby and co-sponsored by CAWG.

“California’s water supply is becoming alarmingly scarce due to changes brought on by climate change, and groundwater recharge is an essential tool to address these challenges,” said Senator Ashby in a press release.

“The ability in wet times to store water underground to be used in dry years is central to the ability to conjunctively manage groundwater and surface water supplies,” she added. “SB 659 sets realistic groundwater recharge and storage goals to put our state on track to ensure we have a reliable supply of water for the environment, our communities and California industries.”

The legislation was passed by the state legislature and went into effect on Jan. 1, 2024.

“SB 659 represents the most significant effort since creation of the Sustainable Groundwater Management Act in 2014 in emphasizing the supply side of managing groundwater,” said CAWG President Natalie Collins in a press release.

“Now we’re looking at expanding that,” Miiller said. “Now we’ve got to figure out how do we make that happen in practice. How do we help reach that goal? What are the policies we could put in place to help achieve that goal?”

Housing for Ag Workers
“We’re also looking at things like revisiting the housing issue,” Miiller said. “What can we do to provide more housing for ag workers? That’s something that we’re going to look at addressing again in 2025.”
However, the state legislature is reluctant to take that issue on, according to Miiller.

“There were a few small bills that were passed last year that we supported, but they’re kind of around the edges,” he said. “They don’t really deal with the bigger problem. We just have a lack of affordable housing for ag workers.”

As things currently stand, many ag workers have to drive two hours to work because they can’t afford to live where they’re working, according to Miiller.

“There are a couple of challenges with housing: One is the NIMBYs (people who say, ‘not in my backyard’) are very strong in in local communities,” he explained.

Miiller used the situation in Half Moon Bay as an example of the problem for ag workers. A mobile housing development was under construction after the tragic murders that occurred in ag worker housing there.

“The city government said, ‘We don’t want to build housing here because we think that the protection of the coast is more important,’” he said. “So, they were looking at the coastal zone and environmental laws, and giving that a higher value than meeting the housing needs of their community.”

Miiller called that “a subjective analysis to how you build housing” because people there view affordable housing for ag workers as something negative. “We view it as you need more affordable housing for ag workers.

“It is a tough industry right now,” Miiller said. “The market for winegrapes is down, and we’re looking at probably taking out about 50,000 acres of winegrapes statewide. If you take out winegrapes and take out vineyards, there’s an opportunity to build housing on that same land for ag workers who are working in other vineyards or in other commodities, but to do that is very difficult.”

The challenges are in getting the permits, getting everything done, and “fighting the NIMBYs,” he said. “But it’s also difficult in the financing, and so we need to really make that a higher priority.”

Currently, the Joe Serna, Jr. Farmworker Housing Grant Program helps to fund the construction, renovation and acquisition of housing for ag workers. Assistance is offered in the form of deferred-payment loans for multifamily housing and grants for new single-family housing.

“That fund, frankly, needs more funding,” Miiller said. “It needs to increase dollars to help support ag worker housing. It should be ag worker housing on ag land, where it’s closer to where people are working so people aren’t driving two hours to work. Those are the things we’d like to see the legislature really take on.”

Miiller said the first step toward more affordable housing for ag workers would be streamlining the permitting process.

“We did a bill last year that we may revisit,” he said. “This is [Assemblymember Carlos] Villapudua’s legislation that we couldn’t get a hearing on. The committee wouldn’t even hear it because they just don’t like the idea of building ag worker housing on ag land. They think this should all be run by nonprofits or local governments, and we don’t object to that, per se, but it hasn’t happened. So if nonprofits and local governments aren’t stepping up to build the housing, then we think you should really look at the growers who are willing to do that and make it easier for that to happen.”

Villapudua initially had registered to run for reelection in Assembly District 13 but following some political maneuvering before the election, will be replaced.

“So, we’ll be looking for somebody else next year,” Miiller said. “The legislature doesn’t even come back in until January, so we have some time to figure out how we’re going to approach it.”

SB 1135, introduced last year by State Senator Monique Limón, would make it easier for growers to increase composting on their farms. California Association of Winegrape Growers Director of Government Relations Michael Miiller said the organization will work with Limón on this front in 2025.

Composting
“We’re also looking at things like composting on agricultural land,” Miiller said. “We know we have the ability to create healthy soils by doing some carbon sequestration on ag land.”

Increased composting offers environmental benefits as well as climate change benefits, he said, “but we need to make it easier for growers to compost.”

Miiller suggested a tax credit to subsidize some of that cost, adding expediting the permit process would also help.

“We’re still looking at what to do with that,” he said. “We did a tax credit last year that didn’t make it through, but we’ll be revisiting what we want to do with that again next year.”

State Senator Monique Limón was the author of SB 1135, the bill introduced last year that would have made it easier for growers to increase composting on their farms.

“She was a great author,” Miiller said. “She worked very hard on that bill last year, so obviously she’s somebody we’d want to talk to first.”

Senator Limón, who represents Senate District 19, which includes Santa Barbara and the surrounding winegrape-growing areas, seems receptive to introducing a compost bill in the state senate next year.

“[Senate District] 19 is a leading producer in the wine industry for our state, and for that reason I want to ensure our farmers and winemakers are able to find ways to divert organic wastes from landfills in a cost-effective manner,” she said. “Compost is expensive to produce, transport and apply to the land, making it a significant barrier for far too many. SB 1135 would have provided an economic incentive to utilize the practice of composting by providing a tax credit to cover costs associated with composting.

“At this point in time, I am working with my team to solidify our legislative package and would be open to the idea of continuing our work on this issue from 2024,” she added. “With that said, California is currently facing a budget shortfall making it challenging to pass tax credits.”

“I would just say, generally, winegrape growers are having a hard year,” Miiller said. “Obviously, the whole industry globally is having a difficult time and we are looking for legislative opportunities to help make things easier for growers. We’re trying to also deal with legislation that’s coming down the pipe that may be challenging for them, but we’re going to try to engage in those to protect our growers’ interests.”

Forward-Thinking Ag Tech for Improved Vineyard Autonomy

By
Pam Strayer | Contributing Writer
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Naio’s TED autonomous weeder demonstrated at Robert Hall Winery in Paso Robles

Dozens of forward-thinking ag tech companies showed off next gen vineyard solutions and products at the third annual FIRA-USA expo, held October 22-24 in Woodland. Solar-powered, real-time spore detectors, AI-enabled drones and electric autonomous tractors all strutted their stuff, giving glimpses of what many larger growers are already trialing behind the scenes.

Afternoon demos provided real-world examples of advanced technology ranging from Chinese-designed MQ Technologies’ orange carrier robot to the NAIO over-the-vine platform widely used in France, though most solutions were made in the U.S.

Equipment Highlights: Filling the Labor Gap
State-of-the-art solutions are works in progress approaching the ag tech field from many different angles and ideas. Top vendors demonstrated their equipment at the show.

The Amos tractor is autonomous and runs on 90 continuous hp from three electric-powered motors (photo by P. Strayer.)

Amos Power: A 90-hp Autonomous Electric Tractor

While the Monarch tractor was early to market in California, many growers have found its power too limited for their needs. They were excitedly looking at the Amos tractor designed by former John Deere engineer Tom Boe, who runs Amos Power from his base in Iowa. Introduced to the vineyard community in 2022, when it was demoed in Lodi and Napa, the tractor has been redesigned and upgraded and uses an Xbox remote to control it.

“The military told us, ‘Don’t waste time buying really expensive remotes. Just use Xbox. People understand them,’” Boe said.

For the sake of comparison, Amos is about double the horsepower of a Monarch, Boe estimated.

Amos has a battery life of 8 hours and takes about 8 hours to recharge. The whole thing weighs 7,200 lbs.

“That battery weighs probably about 2,500 of it,” Boe said. For that reason, changing the battery is an unwieldy task requiring equipment to raise and lower it once removed.

It costs $225,000.

“I think you’re going to start to see the electric power is going to start to pencil out pretty well,” said Boe, “when you compare that to diesel fuel.”

Labor savings are the biggest payoff, he said.

“Cal/OSHA has pretty much said they don’t regulate a farm field unless there’s humans in there, right?  So, you can shut the field down, do a quick drive through, make sure there’s no humans, document it’s got no humans, and then OSHA doesn’t regulate it,” Boe said.

Boe said no one is taking jobs away from workers. “There are definitely people that say, ‘What about my job?’ But at the same time, there’s a lot of people that are saying, ‘We don’t have anybody showing up,’ right? People decided to quit showing up, so we’re filling the void as they quit showing up.

Agtonomy tractors in a client’s vineyard. The software can control multiple tractors (photo courtesy Agtonomy.)

“We restrict our entire tractor to continuous horsepower. We never even go into the peak range. And the reason is we designed the entire tractor to be able to hit continuous horsepower, very close to 100 horsepower. It’s 90 [hp], what we measure, it’s 90 continuous horsepower,” he said.

“It doesn’t have a clutch and gear system. It does have three motors. We are, for the most part, the only electric tractor company that did that. Everybody else took an existing tractor, took the diesel out, put an electric motor in and powered the motor.”

After the FIRA show, Boe was busy doing demos all over California in Suisun Valley, Napa, Lodi, Livermore and Santa Maria.

Amos tractors are built in California’s Central Valley.

Monterey Pacific, which farms 16,000 acres of vineyards in Monterey and San Luis Obispo counties, has ordered one, Boe said.

Agtonomy: AI-Enabled Software Solution

Founded by Geyserville grower and vintner Tim Bucher of Trattore Farms, Agtonomy’s product is state-of-the-art artificial intelligence-enabled automation software used to control tractors growers already use.

In a show of force in an afternoon demo at FIRA, Agtonomy deployed three Doosan Bobcat tractors moving simultaneously and autonomously through parallel vineyard rows. They were all controlled from a single device.

In May, the company announced that Jorge Heraud, formerly John Deere’s vice president of automation and autonomy, joined Agtonomy’s board.

The company announced in October it has raised a total of $32 million from investors, making it one of the more well-capitalized new companies.

The company’s units are currently in use in trials with E. & J. Gallo, Silver Oak, Treasury Wine Estates and others. The company reports it has 25 units in service. Pricing ranges from $50,000 to $100,000.

Naio Technologies
Founded in 2011, Toulouse-based Naio Technologies in southern France is one of the more established robot companies in the vineyard robot world. Its co-founders also founded the FIRA expo.

“The robot offers effective and precise mechanical weeding, without herbicides, which respects your soil and crops,” said a company spokesperson via email. “We have dozens of TED robots at work in France and several in other European countries.”

Its two vineyard robots are JO and TED. Both come with five-year warranties.

JO is designed for narrower rows (one meter) and is half the price of a TED.

While state-of-the-art vineyard tech geeks have admired NAIO, it was not available in California until October, having just passed its FCC test.

Caine Thompson, general manager of O’Neill Vintners & Distilleries’ Robert Hall Winery, tried Naio’s TED out on the winery’s Paso Robles vines. “It’s an impressive machine that provides effective and accurate autonomous undervine weed control,” he said. “We found the quality of weeding was excellent through the various tool options available, which made it a simple machine to operate.”

A video demo featuring the French producer is on YouTube at youtube.com/watch?v=aal7XQ_9xcU.

2025 Global FIRA and FIRA-USA
The 2025 World FIRA expo will be held February 4-6 in Toulouse, France. More information is at world-fira.com.

The FIRA-USA event is a three-way partnership with GOFAR (a French nonprofit that runs the global FIRA agtech robotics show in Toulouse), UC ANR (and its innovation group The Vine) and Western Growers Association and its 2,200 grower-members. Next year, it will be held once again at the Yolo County Fairgrounds in Woodland in the fall.

“I was impressed by the FIRA event, especially since it is so young,” said Eric Pooler, vice president, viticulture, winery relations and bulk wine sales for Nuveen Natural Capital. “Vanguard technology, interactive demos and an impressive lineup of speakers broaching pertinent topics made it a valuable use of my time. The location in Woodland was excellent, too; relatively central for North State growers. It’ll be a do-not-miss for me in 2025.

Field-Scale Ultraviolet-C Light Applications to Manage Grapevine Powdery Mildew in Eastern Washington

By
Alexa McDaniels, Ph.D. | Research Scholar, Viticulture Research and Extension, Dept. of Horticultural Science, North Carolina State University
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Over-the-row ultraviolet-C light (UV-C) array applying a UV-C dose of 200 J/m2 to Vitis Vinifera ‘Chardonnay’ grapevines for management of grapevine powdery mildew. Tractor driver is wearing proper personnel protective equipment (clothes and gloves that cover all skin with ANSI Z87.1 rated eyeglasses and face shield). Shown are applications made at early shoot growth (left) and applications made at post-bloom (right) (all photos courtesy A. McDaniels.)

Ultraviolet-C light (UV-C) for crop protection is not a new concept, but how we integrate the technology into pest and disease management programs is. Field application of UV-C has successfully reduced powdery mildews of strawberry (Onofre et al. 2021), cantaloupe (Lopes et al. 2023) and grapevine (Ledermann et al. 2021, Gadoury et al. 2023). This was possible due to key findings that enhanced efficacy by applying UV-C during a dark period that continued for at least four hours after application (Janisiewicz et al. 2016a, Suthaparan et al. 2016a, Onofre et al. 2021). This dark period allows the UV-C damage to be permanent by bypassing the robust fungal photolyase repair mechanism that is driven by the blue and UV-A components of sunlight (Beggs 2002). Applying UV-C followed by a dark period (i.e., a lower, non-phytotoxic dose) can be used to suppress pathogens effectively (Suthaparan et al. 2014, 2016b, Janisiewicz et al. 2016b, Onofre et al. 2021). Pioneers in UV-C application for crop protection (David Gadoury with Cornell University and USDA scientists Fumiomi Takeda and Wojciech Janisiewicz) have previously written articles in Progressive Crop Consultant. These articles further describe past UV-C research that has led to the successful application of UV-C.

Our research conducted at Washington State University, led by Michelle Moyer, was in collaboration with Gadoury and Walt Mahaffee with USDA to expand UV-C applications for field-scale pest and disease management in grapevines. Our goal was to expand our knowledge of how UV-C can be used as a non-pesticidal alternative to suppress grapevine powdery mildew (Fig. 1) in Eastern Washington State Vitis vinifera vineyards through testing different timing and intervals for UV-C application. We additionally explored UV-C effects on basic fruit chemistry. The results of our research (McDaniel et al. 2024) are now published open access at American Journal for Viticulture and Enology.

Figure 1. Grapevine powdery mildew (Erysiphe necator) colonizes the surface of any green tissue, making it susceptible to environmental conditions. Powdery mildew appears as white, powdery mass on the surface of the plant. Infection can reduce photosynthesis of leaves (left) and renders fruit (right) unusable due to negative effects on pH, soluble sugars and flavor components.

Experiment Methods
Our field-scale UV-C (Fig. 2) array was based on designs from Gadoury and Mahaffee. It was built as an over-the-row triangular arch with 12 ballasts to power 24 UV-C lamps backed by polished aluminum reflectors. It was supported by a metal tower attached to the three-point hitch system of a tractor. Thick PVC strips were mounted on each end of the array like curtains to contain UV-C within the apparatus. The framework was built by VineTech Equipment in Prosser, Wash. A dose of 200 J/m2 was achieved by adjusting ground speed based upon the array length and mean irradiance at the approximate height of the fruiting zone in the vineyard (Gadoury et al. 2023). UV-C dose is based on how long the vine is exposed; a longer array, slower speed or more bulbs would equal a higher dosage. UV-C treatments were applied 30 minutes post-sunset to allow for an optimal dark period.

Our trials conducted at the WSU research vineyard in Prosser tested UV-C intervals of weekly or twice-weekly in two different timing strategies to manage grapevine powdery mildew from 2020-22. Early season timing trial consisted of UV-C treatments made from early shoot growth to pre-bloom followed by a fungicide spray program post-bloom. Season-long timing trial had UV-C treatments that replaced all fungicides from early shoot growth to three weeks post-fruit set. Early season UV-C treatments were compared against three controls and season-long UV-C treatments were compared against two controls.

Figure 2. Washington State University over-the-row ultraviolet-C light (UV-C) array at the WSU research vineyard in Prosser, Wash.

Treatments for the early season trial:
1) Early weekly UV-C
2) Early twice-weekly UV-C
3) Early unsprayed, no fungicide treatments from early shoot growth till pre-bloom
4) Unsprayed, no fungicide treatments for the season
5) Fungicide program, based off typical spray programs in Eastern Washington Vineyards

Treatments for the Season-long Trial:
1) Weekly UV-C
2) Twice-weekly UV-C
3) Unsprayed, no fungicide treatments for the season
4) Fungicide program, based off typical spray programs in Eastern Washington Vineyards

Grapevine powdery mildew was visually rated as a disease severity percentage on leaves and clusters from bloom and continued until harvest. Severity ratings were converted into an area under disease progress curve (AUDPC), which quantifies disease intensity over time, providing an understanding of how disease accumulates throughout the season. The following berry harvest metrics were measured: yield, soluble solids, titratable acidity and pH. Berry skin tannin and phenolic concentrations were additionally measured from season-long treatments following the Adam-Harbertson Methods (Harbertson et al. 2002, 2003) as phenolics are shown to increase with sunlight exposure.

Results
The hot and dry weather conditions in Eastern Washington State for 2020 and 2021 did not favor grapevine powdery mildew infection. In 2021, the daytime high temperatures from bloom to veraison exceeded 35 degrees C for 17 consecutive days. The 2022 vintage was dramatically different than the previous years, creating a favorable climate for grapevine powdery mildew infection with below-average temperatures and above-average precipitation. The low disease pressure experienced in 2020 and 2021 influenced our ability to evaluate the potential reduction of disease. It is hard to separate disease ratings when low to no disease is present.

Early season UV-C treatments significantly reduced foliar and cluster disease severity relative to the unsprayed control in 2020 and 2022 (Fig. 3). In 2021, due to extended high temperatures throughout the growing season, there was low foliar and no cluster disease in the vineyard, resulting in no separation of UV-C treatments, the fungicide program and untreated vines. Overall, early season UV-C, either weekly or twice-weekly, was as effective as the fungicide program for reducing disease. This indicates UV-C could replace standard fungicides early season in a grapevine powdery mildew management program for Eastern Washington.

Figure 3. Results based on our research published in American Journal for Viticulture and Enology (McDaniel et al. 2024). Foliar and cluster disease severity ratings represented as accumulated area under disease progress curve (AUDPC) for early season treatments. A) and C) 2020 and 2022 foliar disease AUDPC, respectively. B) and D) 2020 and 2022 cluster disease AUDPC, respectively. 2021 foliar and cluster disease is not represented as there was low to no recorded disease. Error bars are standard error (n = 4). Different letters denote significant differences among treatment means at α = 0.05 using Tukey’s honest significant difference test.

Season-long UV-C treatments (Fig. 4) in 2020 did not significantly reduce foliar or cluster AUDPC relative to the unsprayed treatments. In 2021, due to high temperatures and low precipitation, there were no differences between any treatments in foliar AUDPC, and there was no observable disease on clusters regardless of treatment. In 2022, weekly and twice-weekly UV-C applications significantly reduced foliar AUDPC relative to the season-long unsprayed control. Cluster AUDPC in 2022 was significantly reduced with weekly and twice-weekly UV-C applications with twice-weekly UV-C performing the best. In 2022, both UV-C treatments did not significantly reduce foliar, or cluster disease compared to the fungicide program. This leads us to believe that improvements to UV-C application treatments can be improved. Season-long UV-C did not affect the yield, pH, titratable acidity or Brix of the grapes. The effects of season-long UV-C on tannins and phenolics were inconsistent year-to-year, suggesting factors other than UV-C were more influential on these measures. Nonetheless, season-long or exclusive UV-C for grapevine powdery mildew management requires further evaluation under Washington State conditions.

Figure 4. Results based on our research published in American Journal for Viticulture and Enology (McDaniel et al. 2024). Foliar and cluster disease severity ratings represented as accumulated area under disease progress curve (AUDPC) for season-long treatments, including an unsprayed control, a full fungicide program or weekly/twice-weekly ultraviolet-C light (UV-C) treatments. A) and C) 2020 and 2022 foliar disease AUDPC, respectively. B) and D) 2020 and 2022 cluster disease AUDPC, respectively. 2021 foliar and cluster disease is not represented as there was low to no recorded disease. Error bars are standard error (n = 4). Different letters denote significant differences among treatment means for season-long AUDPC (final date) at α = 0.05 using Tukey’s honest significant difference test.

While not always statically significant, the consistent trend in reduction in powdery mildew disease as a result of weekly or twice-weekly UV-C treatment indicates the incorporation of UV-C into a vineyard IPM program could be an effective alternative for powdery mildew management without compromising fruit quality. To improve UV-C efficacy we believe that canopy management could play a critical role. For this experiment, we did not implement any canopy management practices as we were trying to induce grapevine powdery mildew disease. As with many foliar pesticide applications, coverage of the desired target is required for efficacy. A dense and complex canopy architecture (which our canopies were in this experiment) makes access to the fruiting zone a challenge. This might explain the more-consistent disease suppression when UV-C was applied only in the early season as canopies were less dense and allowed greater UV-C penetration. This also suggests UV-C efficacy may respond favorably to pruning and training systems that open canopies and expose the fruiting zone. To allow light (or spray) penetration to the fruiting zone, the following practices are important: shoot training, shoot thinning and leaf removal.

Future Studies
Though we are pleased with these results, considering the benefits and potential negative impacts must be addressed for grower adoption. One main benefit of UV-C is it can be used in rain or wind, making it less environmentally dependent compared to typical pesticide sprays. Another plus, there is immediate reentry after treatment. This technology provides a residue free option, uses no water, and can be used when fungicide resistance is present in populations. All these examples make UV-C a potential tool for a sustainability forward pest management program. The cons to this technology are application is labor-intensive and requires nighttime applications. Management of grapevine powdery mildew with UV-C would demand at least weekly applications, most likely twice-weekly for improved efficacy, which could be a substantial amount of tractor hours. As it is a new tool, it requires either you build it yourself or wait for commercial units. Lastly, the effects to beneficial insects are still unknown. Studies that explore these challenges will be important for grower adoption.

UV-C research is still being continued at WSU within the Moyer lab by graduate student Jesse Stevens based on the results from these findings. They are exploring how canopy management practices, such as shoot thinning and fruit zone leaf removal, can increase the efficacy of UV-C applications for managing grapevine powdery mildew.   

Alexa McDaniel is now a Viticulture Extension and Research Scholar at North Carolina State University where her program aims to provide extension education materials for best viticulture practices and field-applied research focuses on pest and disease management. Additional information on UV-C can be requested from McDaniel (almcdan2@ncsu.edu) or Michelle Moyer (michelle.moyer@wsu.edu).

This work was funded by the Washington State Grape and Wine Research Program. The author would like to thank Bernadette Gagnier, Jake Shrader, Maria Mireles, Charlotte Oliver and Margaret McCoy for their help in this project.

References
Beggs CB. 2002. A quantitative method for evaluating the photo-reactivation of ultraviolet damaged microorganisms. Photochem Photobiol Sci 1:431-437. DOI: 10.1039/B202801H

Harbertson JF, Kennedy JA and Adams DO. 2002. Tannin in skins and seeds of Cabernet Sauvignon, Syrah, and Pinot noir berries during ripening. Am J Enol Vitic 53:54-59. DOI: 10.5344/ajev.2002.53.1.54

Harbertson JF, Picciotto EA and Adams DO. 2003. Measurement of polymeric pigments in grape berry extract sand wines using a protein precipitation assay combined with bisulfite bleaching. Am J Enol Vitic 54:301-306. DOI: 10.5344/ajev.2003.54.4.301

Gadoury DM, Sapkota S, Cadle-Davidson L, Underhill A, McCann T, Gold KM et al. 2023. Effects of nighttime applications of germicidal ultraviolet light upon powdery mildew (Erysiphe necator), downy mildew (Plasmopara viticola), and sour rot of grapevine. Plant Dis 107:1452-1462. DOI: 10.1094/PDIS-04-22-0984-RE

Janisiewicz WJ, Takeda F, Nichols B, Glenn DM, Jurick II WM and Camp MJ. 2016a. Use of low-dose UV-C irradiation to control powdery mildew caused by Podosphaera aphanis on strawberry plants. Can J Plant Pathol 38:430-439. DOI: 10.1080/07060661.2016.1263807

Janisiewicz WJ, Takeda F, Glenn DM, Camp MJ and Jurick II WM. 2016b. Dark period following UV-C treatment enhances killing of Botrytis cinerea conidia and controls gray mold of strawberries. Phytopathology 106:386-394. DOI: 10.1094/PHYTO-09-15-0240-R

Ledermann L, Daouda S, Gouttesoulard C, Aarrouf J and Urban L. 2021. Flashes of UV-C light stimulate defenses of Vitis vinifera L. ‘Chardonnay’ against Erysiphe necator in greenhouse and vineyard conditions. Plant Dis 105:2106-2113. DOI: 10.1094/PDIS-10-20-2229-RE

Lopes UP, Alonzo G, Onofre RB, Melo PP, Vallad GE, Gadoury DM et al. 2023. Effective management of powdery mildew in cantaloupe plants using nighttime applications of UV light. Plant Dis 107:2483-2489. DOI: 10.1094/PDIS-08-22-1941-RE

McDaniel AL, Mireles M, Gadoury D, Collins T and Moyer MM. 2024. Effects of ultraviolet-C light on grapevine powdery mildew and fruit quality in Vitis vinifera Chardonnay. Am J Enol Vitic 75:0750014. DOI: 10.5344/ajev.2024.23071

Onofre RB, Gadoury DM, Stensvand A, Bierman A, Rea M and Peres NA. 2021. Use of ultraviolet light to suppress powdery mildew in strawberry fruit production fields. Plant Dis 105:2402-2409. DOI: 10.1094/PDIS-04-20-0781-RE

Suthaparan A, Stensvand A, Solhaug KA, Torre S, Telfer KH, Ruud AK et al. 2014. Suppression of cucumber powdery mildew (Podosphaera xanthii) by supplemental UV-B radiation in greenhouses can be augmented or reduced by background radiation quality. Plant Dis 98:1349-1357. DOI: 10.1094/PDIS-03-13-0222-RE

Suthaparan A, Solhaug KA, Stensvand A and Gislerød HR. 2016a. Determination of U V action spectra affecting the infection process of Oidium neolycopersici, the cause of tomato powdery mildew. J Photochem Photobiol B 156:41-49. DOI: 10.1016/j.jphotobiol.2016.01.009

Suthaparan A, Solhaug KA, Bjugstad N, Gislerød HR, Gadoury DM and Stensvand A. 2016b. Suppression of powdery mildews by UV-B: Application frequency and timing, dose, reflectance, and automation. Plant Dis 100:1643-1650. DOI: 10.1094/PDIS-12-15-1440-RE

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