- Author: Emily C. Dooley, UC Davis
Project designed to prevent red blotch and other grapevine diseases
A new, $5.25 million greenhouse is being built on the University of California, Davis, campus to safeguard an important grapevine collection from red blotch disease and other pathogens.
The 14,400-square-foot greenhouse will have a vestibuled entry, be insect-proof and provide another level of disease protection. It is being spearheaded by Foundation Plant Services, or FPS, which provides the U.S. grape industry with high-quality, virus-tested grapevine plant material.
The program serves as the primary source for grapevine plant material distributed to nurseries under the California Department of Agriculture's Grapevine Registration and Certification Program, which provides the majority of grapevines planted in the United States. For the grape industry, it is essential to protect this material from disease-carrying insects and guarantee fast access to clean plant material.
“The program is considered the largest quarantine center for the grapevine industry in the United States,” said Maher Al Rwahnih, a plant pathologist and FPS director. “This is kind of a game changer for us.”
A history of serving the grapevine industry
FPS has maintained healthy grapevine planting stock on the UC Davis campus for more than 70 years in open fields at the Classic and Russell Ranch foundation vineyards. FPS scientists first detected grapevine red blotch virus at Russell Ranch in 2017. By 2021, an estimated 51.6% of the crop there was infected. Material from that vineyard is not being sold, and the site is now part of an epidemiological study to try to pinpoint how the disease is transmitted.
FPS pathologists have detected red blotch on less than 1% of the Classic vineyard crop. But it may not always be that way in the future.
“We don't know how long the Classic vineyard will remain clean,” Al Rwahnih said. “Every testing season, this is what keeps me up at night. We're not sure why it's happening in Russell Ranch and not the Classic vineyard.”
Once the greenhouse is operating, grapevines propagated from plant material from the Classic vineyard will be moved into the greenhouse, tested and verified as clean from disease. From there it will be sold to nurseries, which will grow additional plants to sell to growers.
Two greenhouses part of plan
Normally the foundation has 4,000 vines available, but the greenhouse will only house 2,000 vines, so inventory will be cut in half.
“This phase is just a starting phase,” Al Rwahnih said. “It's not sufficient for our needs.”
FPS plans to build another greenhouse in the next two to three years to increase capacity.
Industry groups and FPS identified greenhouses as the best way to protect the plants from red blotch and other pathogens transmitted by insects. They are also consulting with those same people on the grape varieties to include in the greenhouse.
“We have a large selection, and we need to make sure all the varieties that are important to industry are contained,” he said.
The first greenhouse is expected to be finished by the end of 2023.
Funding for the first greenhouse is coming from a variety of sources. The California Fruit Tree, Nut Tree and Grapevine Improvement Advisory Board, managed by the California Department of Food and Agriculture, contributed $4 million to the project. The California Grape Rootstock Research Foundation gave $500,000, Foundation Plant Services with UC Davis is funding $450,000, and the California Grape Rootstock Commission gave $100,000.
“This is crucial for the grapevine industry, and we are very grateful for the support,” Al Rwahnih said.
/h3>/h3>/h3>- Author: Tony Nunes, UC Master Gardener
By Tony Nunes, U.C. Master Gardener of Napa County
Knowing basic botany and grapevine structure and selecting a variety and rootstock suited to the location can help vineyard owners succeed. Master Gardeners call it putting the right plant in the right place.
We are fortunate to live in a region with soil types and microclimates that produce world-class wines. Just like commercial vineyard managers, home vineyard owners need to make decisions based on their unique site, goals and conditions and make adjustments driven by Mother Nature throughout each growing season.
It starts with a vineyard management plan for the season. Napa Valley has kicked off the year with rainfall amounts and low temperatures not seen in many years. Determining pruning dates is the first step. In some places, pruning has already started as vineyard managers allocate their resources throughout the valley.
Home vineyard owners may have the flexibility to delay pruning, which in turn delays bud break and minimizes the potential for damage from a late frost. Some people make two passes, first to remove last year's old canes, then to make the final command decision: the pruning of buds created during the 2016 growing season that will produce the crop for this year's harvest.
As our growing season progresses, days get longer, soil temperatures rise and grapevine sap begins to flow. This awakening from winter dormancy is one of many milestones of the growing season.
One element of integrated pest management is a plan for controlling powdery mildew (Uncinula necator) and botrytis (Botrytis cinerea) from bud break to veraison, the color change in grapes that signals the onset of ripening. The spores that cause powdery mildew or botrytis are ubiquitous in Napa Valley vineyards.
Powdery mildew infections from the previous year appear as a blue fungus on individual berries or clusters. Botrytis affects the internal tissues of the berry or the entire cluster. Berries split and fungal spores can grow out of split skins. The spores from infected clusters are distributed easily by wind. Spores can survive the winter on the grapevine bark and cause infections the following year.
Early in the growing season, vine shoots grow rapidly. Like a jack-in-the-box, buds produce shoots and a self-pollinating flower blooms to produce the year's crop. Bloom and fruit set are critical periods driving yield and fruit quality. Temperature swings and rain are not welcome during this time.
Grapevines do not required special fertilizers but should be kept in balance with nutrients available in the soil. Too much nitrogen in the soil can cause vines to produce excess canopy, creating issues with pest management and crop quality.
When applying fertilizer, first ask yourself why. Testing can help you determine what the vine needs. The first test of the growing season, petiole testing, should be performed after fruit set. Petioles connect leaf blades to the vine shoot. Samples of 25 to 50 petioles are selected for each block and tested to determine what nutrients might be deficient or present in excess. Fertilizers are then applied according to the specific needs of that block.
Grape clusters need leaves and sunshine to ripen the crop. Additionally, new buds require sunshine to produce energy for next year's crop. Managing the amount of leaves and their health is referred to as canopy management.
Removing leaves at the base of the canes surrounding grape bunches allows for better sunlight penetration and airflow. To guide decisions about leaf removal, growers observe weather conditions and how the vineyards are oriented to the sun. Leaf removal on the west side facing the afternoon sun is limited during July and August to minimize sunburn and bunch rot. Home grape growers may also need to observe their microclimates or placement of buildings when determining how to manage the canopy.
Irrigation decisions also affect canopy health. Vineyard managers monitor soil moisture levels and visual clues from leaf blades and tendrils during the early season's rapid shoot growth, flowering and fruit set. When irrigation is needed, it is best to irrigate deeply according to the site's soil-moisture holding capacity.
Roots don't grow in dry soil. The goal is to encourage roots to grow as deeply as possible given the site's soil conditions, with just enough water stress to produce high-quality fruit.
Home vineyard owners are generally optimists or at least try to be. Each year, they look forward to a successful harvest, drawing on the knowledge gained from previous growing seasons.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.
- Author: Jeannette E. Warnert
In 2008, UC Cooperative Extension specialist Jim Wolpert and staff research associate Mike Anderson identified red blotch as a disease caused by a distinct virus. Since then, it has been found in numerous California regions, as well as 11 other states, including all major U.S wine states.
As suggested by its name, the disease turns grape leaves a blotchy red color. The infected grapevines may produce clusters with reduced sugar content, causing delayed harvests. Poor color development and increased acidity are found in some clusters on diseased vines. There is no cure.
The Wine Spectator article said UC Davis and USDA Agricultural Research Service may have made a breakthrough in understanding how the disease is spread. After running experiments with various insects found in infected vineyards, they theorize that the three-cornered alfalfa treehopper is a probable vector for the disease. Greenhouse-raised, disease-free control vines were found to have contracted red blotch after exposure to treehoppers from infected vineyards.
The treehopper mostly feeds on plants near vineyards — fruit trees and grasses. It sometimes feeds on leaves, but was considered a minor pest. If the treehopper is the disease vector, farmers will have a target for treatments that could slow the spread of red blotch.
"Management strategies so far have relied exclusively on careful selection of clean planting materials from virus-tested stocks," said Marc Fuchs of the School of Integrative Plant Science at Cornell University. "So the identification of the three-cornered alfalfa treehopper as a vector is putting researchers in a position to develop more effective management strategies."
- Author: Pat Bailey
The virus is of particular concern to wine grape growers, whose grapes must reach a certain sugar content level before they are suitable for winemaking.
"The most urgent research need now is to determine how the virus spreads," said Deborah Golino, UC Cooperative Extension specialist in the Department of Plant Pathology at UC Davis and director of the UC Davis-based Foundation Plant Services.
"Due to the distribution of the virus in many parts of the United States and evidence that it can be transmitted by grafting, we suspect that red blotch disease is widespread wherever grapes are grown," Golino said.
Golino encouraged vineyard owners and managers to evaluate their vineyards for red blotch disease as they would for any other viruses.
Symptoms include blotches of pink or red veins on green leaves in the fall, when grape leaves would normally be turning a uniform gold color. Growers also might notice that their grapes are slow to develop sugar levels sufficient for winemaking, with some grapes never fully maturing.
"If there are visual signs of red blotch, as well as poor sugar development, growers should test their vines for both red blotch and leafroll virus because the symptoms of the two viruses are so similar," Golino said.
She reported that red blotch disease has been identified among both young and mature grape vineyards in California, New York, Virginia, Maryland, Pennsylvania, Texas and Washington. A virus almost genetically identical to red blotch also was found in Canada.
While the virus, also called grapevine red blotch-associated virus or GRBaV, likely can be found in all types of grapes, including rootstock, and table and raisin grapes, it was first detected in wine grapes because they are carefully monitored for sugar content to determine harvest date.
Presence of the virus in a vine can be confirmed using an extremely sensitive laboratory test known as polymerase chain reaction, or PCR, to detect small amounts of genetic material. This analytical process uses an amplification technique that multiplies the existing DNA and similar genetic material to identify the virus.
"If the vineyard tests positive for red blotch, the grower needs to decide, from an economic standpoint, when is the best time to remove the diseased vines and replant the vineyard," Golino said. "This is always a complex decision, and there is no one-case-fits-all answer."
Golino said that the Foundation Plant Services' Classic Foundation vineyard block, used for producing disease-free scion and rootstock vines, has been partially tested and appears to have a very low-level incidence of red blotch virus. Only three of the 1,600 vines tested to date were found to have the virus. Testing of all of the vines in the Classic Foundation vineyard, the source of the majority of grapevine nursery stock in California, is slated for completion in the months to come.
"The good news is that our new Russell Ranch Foundation Vineyard block has been tested, and there is no sign of red blotch virus in any of those vines," Golino said. This vineyard is propagated exclusively with vines that have been through tissue-culture therapy to exclude red blotch and other viruses. Test records from the Foundation Plant Services vineyards are available at http://fps.ucdavis.edu.
Golino cautioned that many more new viruses and other microbes are likely to be found in grapevines in the next few years, thanks to powerful new DNA sequencing technology.
"Some of those will be disease agents, some beneficial, and some neutral," she said. "We will have our work cut out for us in understanding the role of these microbes, but the ultimate result will be increased ability to create superior vineyards."
"The appearance of red blotch virus underscores the vital importance of the Foundation Plant Services and adequate funding for USDA's National Clean Plant Network," said John Aguirre, president of California Association of Winegrape Growers. "Growers need clean plant material to meet winery demands for increased winegrape production and improved quality."
Golino said that progress on identifying and characterizing red blotch has been a collaborative effort between many university-based researchers over the years.
Red blotch disease was first recognized in 2008 in a Napa Valley vineyard by Jim Wolpert, a UC Davis-based Cooperative Extension viticulturist, and Mike Anderson, a viticulture researcher and manager of UC Davis' Oakville Experiment Station.
Two UC Davis scientists - Mysore Sudarshana , a U.S. Department of Agriculture researcher in the plant pathology department, and Maher Al Rwahnih, a researcher at Foundation Plant Services - teamed up in an effort to identify the virus causing red blotch disease. Al Rwahnih was an early user of next-generation, or high-throughput DNA sequencing technology.
During today's meeting, Golino announced that California rootstock nurserymen acted last week to assist the California viticulture industry with research addressing GRBaV. The California Grape Rootstock Research Foundation, which funds research to enhance California viticulture and the grape nursery industry, has agreed to provide seed money to jumpstart research on the virus.
More information on red blotch disease is available on the University of California Integrated Viticulture website.
Foundation Plant Services is a self-supporting unit of the College of Agricultural and Environmental Sciences at UC Davis. The service, dedicated to the distribution of disease-tested, true-to-identity plant materials produced by UC researchers, plays a key national and international role in distributing new crop varieties and healthy planting stocks.
About UC Davis
For more than 100 years, UC Davis has engaged in teaching, research and public service that matter to California and transform the world.
Located close to the state capital, UC Davis has more than 33,000 students, more than 2,500 faculty and more than 21,000 staff, an annual research budget of nearly $750 million, a comprehensive health system and 13 specialized research centers. The university offers interdisciplinary graduate study and more than 100 undergraduate majors in four colleges -- Agricultural and Environmental Sciences, Biological Sciences, Engineering, and Letters and Science. It also houses six professional schools -- Education, Law, Management, Medicine, Veterinary Medicine and the Betty Irene Moore School of Nursing.
Media contacts:
- Deborah Golino, Foundation Plant Services, (530) 754-8102, dagolino@ucdavis.edu
- Pat Bailey, UC Davis News Service, (530) 752-9843, pjbailey@ucdavis.edu
- Author: Stephen J. Vasquez
At a recent meeting held at UC Davis titled “Current Issues in Vineyard Health”, a newly-discovered viral disease being expressed in California’s vineyards was discussed. Currently named ‘Red Blotch Disease’, its symptoms distinguish it from leafroll virus expression, as does its PCR fingerprint. Presently, the most complete information available on the disease can be found in a brochure developed by Jim Wolpert, Viticulture Extension Specialist, UC Davis and Mysore Sudarshana, Plant Pathologist, USDA-ARS, UC Davis.
If you experienced low soluble solids (Brix) or had lower than expected yields in 2012 that cannot be explained, you might want to learn more about Red Blotch Disease.
LEARN MORE:
http://ucanr.edu/red-blotch-disease-2012