Cold Hardiness Prediction, Leafroll Virus, Winemakers’ Tour

Cold-hardiness Prediction Model is (Almost) Ready for Grower Use

John Ferguson explains the complexities of plant dormancy and cold hardiness.
John Ferguson explains the complexities of plant dormancy and cold hardiness.

For vineyard managers, watching the thermometer during eastern Washington winters is a bit like watching their charges dance the limbo: how low can they go? You don’t really want to find out; you just want to know in advance if you need to take frost protection measures.

That’s precisely the focus of a cold-hardiness prediction model being developed by John Ferguson, a WSU staff member based at the Irrigated Agriculture Research and Extension Center in Prosser. He has been analyzing 20-plus years of cold hardiness and weather data collected at Prosser research vineyards. After examining a wide range of parameters, he’s noticed some very interesting patterns. Harnessing a simple but powerful algorithm, he’s turned those patterns into a working model that predicts when a particular grape variety in dormancy will freeze its buds off — and thus when, and in which blocks, vineyard managers should find a way to crank up the heat.

The long-term project also helped get Ferguson lead authorship of a paper published recently in the Annals of Botany. There, he and his co-authors note that the models for Cabernet Sauvignon and Chardonnay have, in stats speak, an r-squared value of 0.89 — in other words, the models are not just statistically valid, they are real-world relevant.

“Developing a cold-hardiness prediction model is an iterative process,” Ferguson says over lunch at the Center. Fortunately, there is a whiteboard on the lunchroom wall, and he soon has it covered with an elegant, multi-colored graph that illustrates the relationship between temperature and cold hardiness and marches inexorably from approaching winter to the following summer. Ferguson has been able to program his number-crunching, stats-analyzing software so that it compares point after time-and-temperature point, each one marking the grapevine’s jagged descent into winter freeze and spring’s subsequent bumpy emergence from dormancy.

What Ferguson has been searching for is the mathematical relationship that best fits the jagged line of time-lapse data collected at the station. His idealized curve — based on a tried and true equation that is useful for modeling all manner of dynamic systems — simplifies the real-world jaggies based on known critical points in the dormancy of grapevines. As he sketches in the key points — growing and chilling degree days and how they are measured, the differing rates of hardening-off among varieties as they reconstitute themselves in preparation for overwintering, and the true point of no return, the temperature when the plant’s natural anti-freeze gives out and, bang, cells in the valuable proto-buds hidden in the dormant wood explode as crystallized ice expands destructively — you begin to realize the enormity of the computational task this man has taken on.

“It would be impossible without computers,” Ferguson said. “When we say ‘iterative methods,’ what we really mean is trial and error. There are billions of calculations involved in fitting the curve around just one set of data for a single variety. To be commercially useful, the model needs to work for lots of data sets for lots of varieties in different locations.” In other words, to be ready for prime time, some serious computational horsepower needs to be strapped to the project. But Ferguson has already made significant progress using a few generations of desktop computers. After all, he’s already developed models for three commercially important grape varieties.

Ferguson is optimistic about a hardware upgrade in the project’s future. “Farmers,” he points out, “are very much into knowing as much as possible. They are attuned to risk. If we can come up with a way to predict hardiness, we can advise growers how to respond — in the winter with heating advisories and, in the spring, with ways to prune in tune with their particular situation.” So far, his work has been funded by a grant from the USDA Viticulture Consortium, as well as funds from WSU Extension and the Chateau Ste. Michelle Distinguished Professorship in Viticulture, the endowed chair held by Ferguson’s boss, Markus Keller. Keller pointed out that, due to cuts in the federal budget, the USDA funds have dried up. Future work on the modeling project will need to be supported by other means.

The power of the cold-hardiness prediction models being developed by Ferguson and his colleagues is immense. But, he reminds us, WSU researchers excel in turning raw data into useful predictive tools. There is AgWeatherNet, the core data collection tool that monitors weather data in real time from more than 130 locations statewide. There are the models developed by entomologists and pathologists that, collated with all that weather data, power a tool that guides growers in making decisions about when, and by what means, to apply management pressure on insect pests and plant diseases. And there is the vast corpus of data on grapevine cold-hardiness that has been collected in Prosser since 1987, primarily by one of Ferguson’s co-authors, Lynn Mills.

Meanwhile, other wine growing regions in North America have adopted the data collection techniques pioneered by WSU viticulturists and are rapidly accumulating mountains of useful information of their own. All of which could feed back into a set of ecosystem management tools that would help growers select viable vineyard sites and manage them in sustainable ways.

Ferguson leaves the lunchroom and its whiteboard; he needs to tend to his computer, to make sure it is still churning data and building models for more grape varieties. “I could probably have done this when I was an undergrad at Michigan State,” he says, referring to the late 1970s. “The theory was certainly there. Of course, I would have needed to tie up all of MSU’s mainframe computing power.”


Learn more about vineyard management tools developed at WSU by visiting

“Dynamic thermal time model of cold hardiness for dormant grapevine buds” by John C. Ferguson, Julie M. Tarara, Lynn J. Mills, Gary G. Grove, and Markus Keller is available online from the Annals of Botany at (login or other registration may be required).

Keller and Lynn Mills won a best paper award from the American Journal of Enology and Viticulture for their work on cold hardiness:

Undergraduate Researcher Makes Progress in Understanding of Grapevine Leafroll Virus

Elizabeth Swanson is an undergraduate researcher majoring in viticulture and enology at WSU Tri-Cities.
Elizabeth Swanson is an undergraduate researcher majoring in viticulture and enology at WSU Tri-Cities.

“There is so much more to viticulture than people think,” said Elizabeth Swanson, who recently bagged a prize for her research on grapevine leafroll disease. Swanson is a viticulture and enology major studying at WSU Tri-Cities. “I’m passionate about wine and what it takes to grow a good quality grape. I feel like blending these two passions was a perfect fit as a career.”

Swanson, who has long had an interest in plants, started undergraduate research during her junior year with her mentor Naidu Rayapati. Rayapati is a virologist and associate professor of plant pathology based at WSU’s Irrigated Agriculture Research and Extension Center in Prosser. Swanson also worked on her research project with Olufemi Alabi, a post-doctoral research associate in Rayapati’s lab. Swanson studies the role of viticultural practices, such as pruning, in regard to the vine-to-vine spread of grapevine leafroll disease, as well as the detection of grapevine viruses in berries using sensitive molecular diagnostic tools.

Leafroll disease is a growing concern for the grape and wine industry because of its negative economic impact. The disease can cause delayed fruit maturity, poor color, and reduced yields. “It can take a long time to detect leafroll viruses in a vineyard,” Swanson said. “It sometimes takes up to a year, so testing a hypothesis takes quite some time. Even though my research is still ongoing, we are seeing that at least one type of the virus, called GLRaV-3, can be detected in sap on shears after pruning.” Contamination of tools is thought to be one means by which the virus spreads.

Last February, Swanson presented her research at the annual meeting of the Washington Association of Wine Grape Growers in Kennewick. Among other things, the WAWGG meeting features research poster presentation sessions. Swanson’s presentation, titled “Studies on Epidemiology of the Grapevine Leafroll Disease,” received first place in the undergraduate research category. The annual meeting is one of the largest industry events in North America and draws attendees from the United States, Canada, and Europe.

“Winning in my category was a nice surprise,” Swanson said. “Attending WAWGG was a good opportunity to share my research with others for the first time. Research is a great opportunity for undergraduates to find out if they want to pursue graduate school or research after graduating,” she said. “Anything you can do to make yourself stand out when you are ready to find a job is helpful. Research has made me more mindful of the scientific method as well as the time and work that goes into research, something I think most of us take for granted.”

Swanson plans to work in vineyard management in the Pacific Northwest after graduation, preferably in Washington state. Her research project was supported in part by a fellowship from the Auvil Family Foundation.

Learn more about Naidu Rayapati’s grapevine leafroll disease research by visiting

Learn more about WSU’s undergraduate program in viticulture and enology by visiting

Tour Argentina and Chile on a Winemakers’ Holiday

A vineyard in the Mendoza region of Argentina.
A vineyard in the Mendoza region of Argentina.

Are you interested in tasting Malbac while sitting in a vineyard in Mendoza, Argentina, or tasting a Chilean Cabernet Sauvignon Gran Reserva while visiting with the winemaker? Then you may be interested in the tour WSU has scheduled to Chile and Argentina wineries and vineyards.

The tour is slated for January 15 – 28, 2012 and is specially designed for Washington winemakers and grape growers. First we’ll visit the most renowned wine regions surrounding Santiago: Maipo Valley, Colchagua Valley, Aconcagua Valley, and Casablanca Valley. Then we’ll fly over the Andes to visit the Mendoza wine region in Argentina.

Free time will allow you to explore the cities of Santiago and Mendoza, the beach at Valparaiso and a resort in the Andes. If you are interested in learning more about this opportunity, please contact Theresa Beaver at

Theresa Beaver is the coordinator for WSU’s professional certificate programs in viticulture and enology; learn more about these professional development programs at

Read “The Mendoza Connection” in Voice of the Vine at

The Return of VEEN, Plus V&E on Facebook

After a long hiatus, a new issue of Viticulture and Enology Extension News — VEEN — is available. It’s a great issue, packed with info for growers and winemakers alike. Check it out at And, while you’re at it, head on over to Facebook and “friend” WSU Viticulture and Enology with a big thumbs up: