Four University of California SJV viticulture farm advisors who started work in the past year include from left Allison FerryAbee  Tulare County Ashraf ElKereamy Kern County George Zhuang Fresno County and Lindsay Jordan Madera Merced and Mariposa counties

Four University of California SJV viticulture farm advisors who started work in the past year include from left: Allison Ferry-Abee, Tulare County; Ashraf El-Kereamy, Kern County; George Zhuang, Fresno County, and Lindsay Jordan, Madera, Merced, and Mariposa counties.

Grapes: Latest on weather stations, nematode control, SJV wine varieties

A way to address frost and heat concerns in vineyards is to alternate vineyard training heights. Biologically-based management strategies for root-knot nematode control are based on improving soil health, organic matter, and water holding capacity.

University of California researchers are using weather stations around the state to get a jump on vineyard pests and to make certain that potentially costly investments in wind machines are a viable alternative to the use of sprinklers for frost protection.

Two speakers discussed weather stations at the annual viticultural roadshow presented in Fresno by the San Joaquin Valley Winegrowers Association. Other topics included the latest in the fight against nematodes.

The meeting closed with a panel discussion centering largely on new wine varieties.

Mark Battany, a UC farm advisor for San Luis Obispo and Santa Barbara counties, discussed how weather stations are used to map temperature inversions for frost protection in the highly variable coastal areas of these counties.

“Today, there is less water available for using sprinklers for frost protection, and we need to look at alternatives,” he said.

One of those alternatives could be a wind machine.

Before shelling out $30,000-$40,000 for that, Battany recommends a $250 device that extends 35 feet into the air and takes temperatures at that height and at five feet above the ground.

Comparing the differences in those temperatures can decide whether the difference created by a wind machine pulling down warmer air aloft is worth the costly investment.

Battany said the devices resemble “tall fishing poles.” Sixty of the towers have been placed in Sonoma, Santa Barbara and San Luis Obispo counties. The 60 towers would fit in the back of a pickup truck.

Since information is logged and retrieved “in real time,” he says the towers are also drawing interest from the National Oceanic and Atmospheric Administration which could use the data for frost forecasting.

Vineyard training height

Another way to address frost and heat concerns in vineyards, Battany says, is to alternate vineyard training heights. At one foot high, the impacts of heat and frost are likely to be greater than at seven feet.

Battany’s research includes temperature sensors at one-foot intervals on an eight-foot-high tower. The temperature differential can be as high as 9 degrees Fahrenheit from the lowest to highest sensor.

Battany would like to see an improvement in the collection of rainfall data for water-limited areas and is looking at the basin that includes the Paso Robles area.

Eighteen rain gauge stations are being placed throughout the basin “to help understand our recharge conditions for that basin.”

He also discussed the interaction between cover crops and water use.

“We need data to manage cover crops to maximize soil water storage,” Battany said. “Cover crops can drain down water.”

Also being explored are evaporative gauges, “a rain gauge in reverse” to track evapotranspiration.

Weather stations for pest, disease control

Lindsay Jordan, a UC farm advisor for Madera, Merced and Mariposa counties, discussed how UC weather stations can be used to help fight pest and disease. She directed workshop participants to www.ipm.ucdavis.edu/weather for information on how to access and use the stations.

Powdery mildew is among diseases that can be addressed by using the site to assist in timing and frequency of the application of fungicides based on a UC Davis powdery mildew index that can be plugged into a formula including data from weather stations.

Using the index and station data can produce time and money savings.

“But the powdery mildew index is not a silver bullet that can be substituted for field observations,” Jordan warned.

Data from stations can also be used to determine if treatment is necessary for the omnivorous leaf roller, she says.

Fighting nematodes in grapes

Andreas Westphal, assistant nematologist at the UC Kearney Ag Center in Parlier, Calif., says ways of fighting nematodes include the development of resistant and tolerant rootstocks, testing new chemical management tools, and developing biologically-based management strategies.

Westphal says root knot nematodes can leave behind galls on roots that “look like a string of pearls.” Nematodes can also damage other parts of the plant that would otherwise be marketable, including potatoes and carrots.

He cites studies from retired specialist Mike McHenry that showed that Movento can be effective in combatting nematodes if certain steps are followed.

A study showed that root-knot nematodes could be most impacted by a four-ounce application of Movento in ruby seedless grapes as compared to 6.25 ounces or if the vineyard were left untreated.

Westphal says nematode population levels are most impacted with a nine-day wait between spraying and resuming irrigation. It’s best, he says, to make single annual treatments with Movento in sandy loam soil and not repeat the treatment.

He says biologically-based management strategies are based on improving soil health, organic matter, and water holding capacity. Cover crops can be used to improve rooting depth.

SJV wine grape varieties

The meeting closed with a panel discussion featuring Emilio Miranda, a viticulturist with Allied Grape Growers in Fresno, and two growers who also operate wineries - Rich Hammond with Moravia Wines in Kerman, and Nathan Cardella with Cardella Winery in Mendota.

Matthew Fidelibus, a UC Cooperative Extension specialist at Kearney, moderated the discussion. Among his questions was whether new wine varieties being researched at Kearney hold any promise for the San Joaquin Valley (SJV).

The three panelists agreed that it is toughest to introduce new varieties for mainstream marketing, but wineries with tasting rooms and clubs can have more success producing wines with smaller fruit quantities that are not mainstream.

They agreed that the quantity of production is a major concern in the production of grapes sold on a mass scale.

Cardella said, “It is hard to knock mainstream varieties” like Cabernet Sauvignon “off their pedestal,” but those who frequent tasting rooms find appeal in varieties including Petite Syrah, Sangiovese, and Ruby Cabernet.

Miranda says new varieties that show some potential for larger-scale SJV growers include the high yielders Cabernet Dorsa and Teroldego.

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