- Author: Pamela Kan-Rice
On Feb. 19, San Joaquin Valley grape growers are invited to discuss the latest UC research on mechanical pruning, trunk disease and rootstocks with UC Cooperative Extension advisors and specialists in Fresno. Growers will also get to observe a field demonstration of grapevines being mechanically pruned.
“We have been hearing from California grape growers that they are having a hard time finding enough workers to maintain their vineyards and increasing labor cost starts challenging grape-farming economic sustainability so we are studying the use of machines to reduce the number of people needed to perform tasks such as pruning,” said George Zhuang, UC Cooperative Extension viticulture advisor for Fresno County.
Gabriel Torres, UC Cooperative Extension viticulture advisor for Tulare and Kings counties, will discuss plant diseases that may result from trunk injuries and pruning wounds from the machinery.
Karl Lund, UC Cooperative Extension viticulture advisor for Mariposa, Merced and Madera counties, will discuss how to select rootstock for a vineyard that will be mechanically managed.
“Because the canopy architecture and yield characteristics from mechanically pruned vines are much different from hand-pruned vines, the water and fertilizer requirements of mechanically pruned vines can be quite different,” Zhuang said. “Therefore, performance of different rootstocks under mechanical pruning system is critical to achieve both yield and fruit quality targets of grape production in the San Joaquin Valley.”
Kaan Kurtural, UC Cooperative Extension viticulture specialist in the UC Davis Department of Viticulture and Enology, will go over the basic principles of mechanical pruning of wine grape vines.
From 8 a.m. to 10:30 a.m., UC Cooperative Extension advisors and specialists will meet with growers in a Golden State Vintners vineyard at 7409 W Central Ave in Fresno.
“We will discuss current grape issues and the future of viticulture in the valley,” Zhuang said.
The meeting, which is being co-hosted by UC Cooperative Extension and San Joaquin Valley Winegrowers Association, is free. For more information, contact Zhuang at firstname.lastname@example.org or (559) 241-7506.
- Author: Pamela Kan-Rice
Recent surveys in the North Coast have found that 90 percent of the powdery mildew samples collected were resistant to strobulurin fungicides, the director of UC Integrated Pest Management Program told legislators at a joint hearing of the California Assembly and Senate Select Committees on California's Wine Industry. A potential solution is breeding winegrapes to be resistant to powdery mildew, but a drawback is that the wine industry is largely known for its varietals.
“Professor Andy Walker at UC Davis has succeeded in crossing winegrapes with a wild grape species that is naturally resistant to powdery mildew and then crossing the offspring back to the parent winegrape variety for several generations,” said James Farrar, who was invited to speak at the committees' informational hearing on “Fire Recovery and Pest Management Awareness” at UC Santa Barbara on Nov. 7.
Farrar warned the legislators of increased human health risks due to “unintended consequences of social pressure” on the herbicide glyphosate, which growers use to control weeds under grapevines rather than tilling the soil, to comply with Natural Resources Conservation Service and Salmon Safe guidelines.
“Recent social pressure resulting from the International Agency for Research on Cancer labeling glyphosate a probable human carcinogen and news stories indicating detection of glyphosate in wine have caused some growers to look at other herbicides,” Farrar said. “The other choices are glufosinate, which is more risky to applicators, less effective, and more expensive, and paraquat, which has similar price and effectiveness, but much greater risk to applicators. Paraquat is a restricted-use pesticide that is highly toxic to humans – 3 teaspoons will kill an adult. It has a higher risk ‘Danger' label in contrast to the lower risk ‘Caution' label for glyphosate.
“This is an increased risk to human health as a result of misplaced public perception of risk.”
Farrar closed his comments by saying, “The County Agricultural Commissioners and county-based University of California Cooperative Extension advisors are vital in the continued efforts to manage winegrape pests and diseases. They are the frontline support for growers and pest control advisers in this effort.”
- 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.
- Contact: Pat Bailey, UC Davis News Service, (530) 752-9843, email@example.com
The study is published in the early edition of the week of Feb. 20 Proceedings of the National Academy of Sciences.
“Many disease-causing microbes can evade one defensive action by a host plant, but we believe that most microbes would have difficulty overcoming a combination of two immune-system defenses,” said the lead researcher Abhaya Dandekar, professor in the Department of Plant Sciences at UC Davis.
He and his colleagues tested this hypothesis on Xylella fastidiosa, the bacteria responsible for Pierce's disease in grapevines. Strains of the bacteria also attack and damage other host plants, including citrus, stone fruits, almonds, oleander, and certain shade trees, such as oaks, elms, maples and sycamores.
The findings further strengthen UC Davis’ standing as a world leader in the science of plant improvement through advances in genetics, genomics, plant breeding and biodiversity.
First noted in California near Anaheim around 1884, Pierce's disease in grapevines is now known to exist in 28 California counties. From 1994 to 2000, the disease destroyed more than 1,000 acres of northern California grapevines, causing $30 million in damages. There is currently no known cure for Pierce’s disease.
In grapevines, Xylella fastidiosa is carried from plant to plant by half-inch-long insects known as sharpshooters. The bacteria infect and clog the plant’s water-transporting tissue, or xylem. Grapevines with Pierce's disease develop yellow and brown leaves and die within a few years.
To block such infections, the researchers engineered a hybrid gene by fusing together two genes that are responsible for two key functions of the plant’s innate immune response: recognizing Xylella fastidiosa as a bacterial invader and destroying its outer membranes, causing the bacteria to die.
The researchers then inserted this hybrid gene into grapevines.
They found that sap from plants genetically engineered with the hybrid gene effectively killed Xylella fastidiosa in the laboratory. And grapevines engineered to carry the hybrid gene had significantly less leaf scorching and xylem clogging, indicating resistance to Pierce’s disease.
The Los Alamos National Laboratory, New Mexico, and the U.S. Department of Agriculture collaborated on the project. Funding came from the state Department of Food and Agriculture’s Pierce’s Disease Program, the U.S. Department of Energy and the U.S. Department of Agriculture.