Fruits of the Vine
Viticulture Field Day Offers Harvest of Science-based Solutions for Growers
John Derrick of Mercer Canyons Inc. didn’t know what was wrong with two blocks of the farm’s 920 acres of wine grapes outside of Prosser last year. Leaves showed reddish discolorations and flecking. He and other vineyard staff speculated about a variety of causes, ranging from a viral infection to chemical damage.
He found the answer at the 2011 Washington Viticulture Field Day at WSU’s Irrigated Agriculture Research and Extension Center. Derrick learned about phosphorus deficiency in wine grapes from one of the presentations—and the leaves in the study looked exactly like those at Mercer Canyons’ vineyard. Applying phosphorus fertilizer fixed the deficiency.
“That field day coincided with what happened in our fields,” Derrick said. “It was very helpful to bring closure to the problem. Today, the fields look fine. There are no deficiencies now.”
Derrick returned to the IAREC on Aug. 10 for more more ideas and discussions at this year’s field day. He joined some 40 other area growers and viticulture stakeholders to hear presentations on managing canopy gaps to minimize production loss, nitrogen treatments in Concord grapes, nematode management, and the complexities of leafroll disease.
Concord Grape Spacing for Higher Yields
Since 2002, WSU Chateau Ste. Michelle Distinguished Professor of Viticulture, Markus Keller and his team have been testing the establishment and performance of Concord grapes planted at various distances within and between vineyard rows with the goal of consistently maximizing crop production while maintaining desirable fruit quality.
Keller and other researchers planted test rows with 8 or 9 feet between them to allow for mechanical pruning and harvesting. Within rows, they spaced plants at 3, 6, 9, and 12 feet apart. Over the long term, the 6-, 9-, and 12-foot vine spacings produced equal amounts of fruit of similar quality.
Time is the only requirement for this approach to managing canopy gaps, so plants can adjust to their new structure. “The plants adapt to the changes in the canopy,” he said. “Roots go deeper, and the trunks get wider. But don’t let weeds take over with wider spacing within rows.”
To Fertilize or Not to Fertilize
WSU soil scientist Joan Davenport discussed nitrogen management and timing in Concord grape. In 2010, Davenport and her research team found that timing nitrogen treatments to the bloom period, when grape plants are taking in nutrients at the highest rate, increases nitrogen use efficiency, reduces the potential for off-target nitrogen movement, and maintains or improves productivity.
Davenport and other researchers also discovered that applying nitrogen post-harvest didn’t result in any increases in yield. So three years ago, she and her WSU team eliminated fall nitrogen application to grapes in the Roza test plots.
“We are still looking at maximum yield and best Brix (fruit sugar content) at treatments of 40 to 60 pounds of nitrogen per acre,” she said.
Another factor to consider is the soil’s temperature in the spring, Davenport explained. The best time to apply nitrogen is when temperatures are above 55 degrees Fahrenheit. Fertilizing when soil temperature is lower is inefficient and doesn’t maximize the grape plant’s uptake of nutrients.
The soil itself also maintains nutrient reserves naturally, she added, which has implications for nitrogen management decisions in vineyards. “There’s something going on in the soil that’s replenishing the system,” Davenport said. “We can actually take advantage of the soil’s reserves of nutrients and limit nitrogen application if applicable.”
Michelle Moyer, WSU viticulture extension specialist, and Amanda Howland, an Oregon State University graduate student, spoke about nematodes associated with Washington grapevines and fumigation alternatives for their management.
Nematodes are a formidable pest of grape. The microscopic, aquatic roundworms live and move in the soil through water, and they can stay in the soil for years without having a plant to feed on, Howland said. They can also burrow as far down as six feet into the soil to avoid the reach of chemical fumigants. Vineyard age, stress, and higher pest populations in a given year can all contribute to an infestation in grape plants. They damage grapes by limiting the plant’s ability to take in water and nutrients, stopping root growth, and killing root tissue, resulting in stunted vines and reduced yields.
Nematode management should start even before planting, by performing soil tests, Moyer said. Those tests can also identify which species is present so growers can tailor treatment. Howland encouraged growers to collect samples in the fall, after nematodes have completed their lifecycle on the grape roots and return to the soil.
“Nematode management is really difficult once the plants are in the ground,” Howland said. “Many alternatives are prevention- or pre-planting-focused, emphasizing the proactive nature of nematode management.”
For already planted vines, a systemic fumigant for mealybug, Movento®, also controls nematodes–at a significant cost, Moyer said. But fumigation alternatives are being sought as researchers learn more about the off-target impacts of certain pesticides. Alternatives to chemical fumigation include mustard and cover crop planting and use of nematode-resistant rootstocks.
White and oriental mustard and other cover crops such as arugula and sudangrass release chemicals that, when incorporated with the soil, kill nematodes. Mustard seed meals also serve as a good nitrogen source.
Ghost in the Vineyard
WSU grape virologist Naidu Rayapati investigates grapevine leafroll disease (GLRD), a complex viral disease of both wine and juice grapes that affects vine health, fruit yield, and fruit quality. Chemicals can’t control it, and it manifests in different, even symptomless, ways, depending on the grape variety, vineyard age, stage of infection, type of virus, viticultural practices, and environmental conditions.
It hides like a ghost in a healthy vineyard until late July or early August. In red wine grapes, leaves turn red, then reddish-purple, and curl in on themselves. In white wine grapes, leaves might yellow or show mottling before they curl—or they might show nothing at all. Because GLRD viruses are predominantly spread through plant cuttings, Rayapati stressed to growers attending the field day the importance of bringing in and planting clean plants. Any new plants introduced into an established vineyard should be guaranteed virus-free from a certified nursery.
“We use laboratory-based methods for the detection of viruses and other graft-transmissible agents,” Rayapati said. “We incorporate state-of-the-art techniques to strengthen our capacity in diagnosing new and emerging disease problems in Washington vineyards.”
Graduate student Brian Bahder discussed his work on developing a faster, more reliable method of monitoring grape mealybug in vineyards. Until recently, growers searched individual vines for adults, a time-consuming task. But the sex pheromone for grape mealybug has been synthesized for use in pheromone-baited traps, which could potentially save growers time and resources. The new traps also show what mealybug populations are doing at any point in the season, which could guide insecticide treatments.
Nella Letizia, text and photos
Washington Viticulture Field Day is sponsored by the Washington State Grape Society and WSU Viticulture and Enology Extension. For more about WSU viticulture and enology research and extension efforts, visit http://bit.ly/RleZSD. To learn about WSGS, visit http://bit.ly/RuDd7u.