New juice grape variety
Sunbelt colors well under high heat, but yields need boosting to make the variety profitable.
Dr. Joan Davenport holds a Concord leaf during a summer field day to emphasize the importance of using whole leaves for nutrient analysis instead of leaf petioles.
A new juice-grape variety under trial has colored well under the hot growing conditions of eastern Washington State, though yields have been disappointing, reported Washington State University's Dr. Markus Keller at a summer field day held at WSU's Roza Research vineyard in Prosser. The field day also highlighted research about optimum vine spacing and nutrition for juice grapes.
Sunbelt, a juice variety developed by the University of Arkansas that was commercially released in the early 1990s, has been under trial in Washington State and California for several years to learn if the variety has potential for West Coast growers. Researchers are interested in the heat tolerance of the variety and have collected data on color, berry composition, fruit characteristics, and yields for the last three years, comparing information to the Concord variety. "Sunbelt gives us much, much better color in hot summers than Concords," Keller said, adding that the berry composition and flavor are pretty much the same as Concord.
But the variety has not been a strong producer in their trials. "The difficulty we've had with this variety so far is that it hasn't cropped as heavily as Concord," Keller said. With the exception of last year, where Sunbelt and Concord had similar cropping levels, yields in the new variety have been 30 percent lower.
The WSU researchers have found that the new variety is similar in winter hardiness to Concord. Sunbelt berries are bigger than Concord, although the clusters are smaller. However, the juice can have twice as much color as Concord.
Keller mechanically pruned the vines during the winter in hopes of increasing production levels of Sunbelt. Previously, the young vines were hand pruned. "We hope to transition the block to minimal pruning to see if we can get the Sunbelt crop levels to the same level as the Concords.
"My thinking is that if we can get the crop levels to ten to twelve tons per acre, it could eventually be interplanted in a Concord block that's in a warm site where a grower consistently struggles with color," Keller said. In some growing seasons that have long periods of high temperatures, Concords can have difficulty acquiring color.
In the WSU Concord research vineyard, an eight-acre block planted in 2003 with support of the Washington State Concord Grape Research Council and industry members, researchers are conducting ongoing trials to study rootstocks, plant density, and nutrition.
Keller has field-grafted some of the Concord vines in the block to the rootstocks 3309 Courderc, Teleki 5C, and 110 Richter to learn if these rootstocks known to be tolerant to high pH conditions could help alleviate chlorosis problems that often plague Washington juice vineyards.
Rootstock 3309, while not chlorosis tolerant, is drought tolerant and was chosen because it is the standard rootstock for Concord vineyards in the eastern United States. Keller noted that 110.R is tolerant of high soil pH, but has not performed well in the trial. They've had "tremendous problems" getting 110.R to establish under Washington's winter conditions. Rootstock 5.C is reasonably tolerant of high pH and high calcium levels, and has shown good vigor, he said, adding that he would recommend it for planting in eastern Washington.
However, the rootstock influence on chlorosis is unknown. "So far, we've had difficulty getting chlorosis in this vineyard," he said, adding that without incidence of chlorosis, they don't know what effect the rootstocks have on minimizing the problem.
When the block was planted in 2003, Keller used different vine spacings to learn if higher density plantings are more profitable in the long term than the industry standard of six feet between vines and nine feet between rows. The trial includes row widths of nine and eight feet, with vine spacing at 3, 6, 9, and 12 feet, with drip irrigation. Individual vines in the trial are tracked each year, with a host of data collectedfruit set percentage, cluster counts, berry size and composition, canopy dimension, and more.
While the vines planted three feet apart produced more in the first few years (an average of 8 tons per acre annually compared to 3 to 4 tons in the 9 and 12 foot spacings), after the initial advantage, the higher density vines produced less per plant and per acre, he found.
Dr. Joan Davenport, WSU soil scientist, is using the Concord research vineyard to study the nutritional and fertility needs of juice grapes. One trial, which began in 2006 and is funded by the Concord Research Council, involves seven nitrogen treatments applied up to four times during the year (as vines break dormancy, bloom, veraison, and postharvest), with application rates ranging from zero to 80 pounds of nitrogen per acre per year at 20-pound increments.
Tissue samples of whole leaves are collected at bloom and veraison and analyzed for total nitrogen. Berry composition at harvest and yield information is also collected from the different treatments.
So far, she said, the trial has confirmed results of previous research, in which whole Concord vines were excavated and analyzed, which showed that the vine uses about 50 pounds of nitrogen per acre to produce an eight-ton crop.
"We are seeing differences in the treatments after the first few years," Davenport said, adding that color and yield reductions have been observed in the 80-pound treatment, particularly from the early spring application. Also, vines have not utilized the postharvest nitrogen applications, confirming earlier belief that postharvest application in the Pacific Northwest is not advantageous.
Her study will last at least four years to allow differences to show up over time. "In a perennial crop like grapes, whatever I do this year, influences the next two years," she said. "Grapes have a long memory."
She notes that WSU sampling guidelines for Washington juice grapes will be changed to recommend that whole leaves be used for tissue analysis. While some growers use petioles for tissue sampling, she explained that the petiole is a straw that tells what is moving between the shoot and leaf. "We're looking for what's being stored in the plant, so we can learn what nutrients the plant does and doesn't have."