California Ag TODAY: Grape Day 2013 Delivers Good Knowledge

Nearly 100 attendees were at the Kearney Agricultural Research and Extension Center today to hear the latest from UC and USDA researchers on many topics.

The early field tour took growers and others in the industry to an on-site grape vineyard to see the effect of water deficits on the productivity of numerous red wine grapes cultivars grown in the San Joaquin Valley.

Larry Williams, UC Davis Department of Viticulture and Enology, is researching big red winegrape varieties, initially started by Jim Wolpert, UC Davis Viticulture Extension Specialist.

Wolpert selected the varieties that looked to have the potential to be grown in the SJV. Now, Williams is working on irrigation management, or the effect of deficit irrigation on wine grape vine growth and wine quality.

What was initially a larger trial of 60 different cultivars from Italy, France, Spain and Portugal, is now 20 different cultivars planted in a new block in which Williams works.

“While these cultivars responded differently to water stress, they all looked good at 50 percent ET for the season,” Williams said.

Other regimes include:

· No water between berry set and veraison. Then at veraison, irrigation was at 50 percent ET.

· Full ET from berry set to veraison and then cut the water off.

“Right now we are seeing visual effects, but we have no definitive answers or recommendations,” Williams said.

“For instance, the cultivar Tanat receives no water from berry set to veraison, and some of the berries are not coloring up. Other varieties are responding in a similar way,” Williams said. “Cabernet and Syrah both looked good under the treatments that were imposed.”

“We will harvest the grapes this week and start to make wine in order to gather data on how treatments affected wine quality,” Williams said.

Moving over to table grape research, Matthew Fidelibus, UC Davis Department of Viticulture and Enology, focused on the effect of pre-harvest calcium chloride and chlorine dioxide applications on Crimson Seedless fruit quality.

He is working with Carlos Crisosto, UC Davis Plant Sciences, on alternative methods for controlling pre-harvest and post-harvest fungi-decay of table grapes using a preharvest application of calcium chloride, and chlorine dioxide.

Fidelibus reported that there were few or no berry or leaf injuries with 0.25 percent calcium chloride; but higher concentrations caused some damage. “Neither calcium chloride nor chlorine dioxide affected fruit quality or field rot incidence (which was very low during the trial),” Fidelibus said. “Both compounds provided some postharvest rot protection of conidi-inoculated fruit, but not nesting- (packed-) inoculated fruit.”

Fidelibus noted that additional testing is needed to determine if the treatments might reduce bunch rots under conditions of higher disease pressure.

Moving into raisin research, Teresa L. O’Keeffe, with USDA ARS, spoke about the ecology of mycotoxin-producing Aspergilli in raisin vineyards. She noted that Black Aspergilli, are commonly observed in agriculture as black molds. “Two species, Aspergillus niger and A. carbonarious are often associated with the microbial complex that causes bunch rot. In fact, A. niger infections can also lead to vine cankers,” O’Keeffe said.

In addition, A. niger and A. carbonarious can be associated with a mycotoxin known as ochratoxin a (OTA) that causes kidney damage in humans if ingested at high enough concentrations.

While there has been very little research conducted in the U.S. on OTA, several EU countries have done testing in both raisins and wine, with results that are well below harmful concentrations.

O’Keeffe noted that recent USDA studies show that even at the highest levels of OTA in both wine and raisins, results are still well below the EU regulatory limits. “By continuing to study vineyards in the SJV, we hope to establish a baseline on how various black Aspergillus species grow and interact with each other during healthy berry development,” she said.

O'Keeffe is a research technician for Jeff Palumbo, a microbiologist with USDA ARS.

Philippe Rolshausen, UC Riverside Specialist, Botany and Plant Sciences, spoke about grapevine wood disease management options on table grapes in the SJV.

“Wood diseases can be a big issue for 20-year-old vineyards, but when problems set into a five-year-old vineyard, there are bigger economic problems at hand,” said Rolshausen.

Control strategies are the same for raisin, table and winegrapes. Esca is the main pathogen that affects table grapes. “This pathogen can be a major problem in table grapes causing loss of wood, cordons, canes, all of which reduce yield,” Rolshausen said. “There can also be a cosmetic impact with necrosis of berries because of the fungi in the vine.”

Rolshausen commented that 2011 was a big year for Esca disease spread due to environmental conditions; mainly rain, during the previous dormant season.

The only way to prevent the disease from infecting the vine is to apply fungicides over the pruning wounds. Manually painting every pruning wound is very labor-intensive and cost prohibitive. “By protecting pruning wounds, you prevent infection,” Rolshausen said.

Rolshausen said that trials suggest that a single tractor spray application with Topsin M, one day following pruning, is able to protect the vine. “Doing this will extend the life of the vineyard by an extra 10 years,” Rolshausen said.

Rolshausen also asked all growers to participate in an online survey, “Management of Measles/Wood Canker Diseases in Table Grape Production.” This survey will gather information regarding wood pathogens in vineyards to assess how they affect grower yields and how growers are dealing with them.

David Haviland stepped to the mic and presented research on the use of Movento in table grapes for controlling vine mealybug and nematodes.

“This is going to be a different talk for me,” he began. “Usually I talk about the efficacy of many different products, but this time I’m only going to talk about one product, Movento, because it is so unique in controlling mealybugs.

“In controlling mealybug, it’s a numbers game, but that’s not all,” he said. “You want to lower the numbers but you do not want what remains to injure your crop.”

Haviland continued, “Reducing crawler movement goes along with overall mealybug management. And while there all several insecticides available for treating mealybugs, such as Movento, Lorsban, Applaud, and Belay (Clutch), it’s important to think about resistance management when choosing any product.”

· Moves across leaf surface

· Mealybug ingests Movento

· Movento starts to inhibit biosynthesis

· Mealybug continues living on existing fat reserves

---Crawlers die within a few days.

---Adult females can survive for 6-8 weeks due to extra fat reserves.

Haviland also described nematode trials using Movento. He noted that:

· Movento definitely has nematicidal effects.

· Movento is best applied in the spring at 6.25 to 9 ounces per acre; however lower rates were more effective in some studies.

· In old, heavily infested vineyards, Movento application for nematodes pays off.

· Yield effects, if any, are unlikely to be seen before year two.

· Use prudence with regard to irrigation as many factors affect systemicity of Movento.

· More data should be available next year to determine the effect of irrigation and girdling on Movento movement.

· Expect results to be highly variable from site to site.

Haviland thanked his SRA, Stephanie Rill, for all her help in his research. He also thanked the Consolidated Central Valley Table Grape Pest and Disease Control District for funding the mealybug research, and the California Table Grape Commission for funding the nematode research.

The final speaker, invited to talk about wine, represented a new approach to Grape Day.

Andrew Waterhouse, UC Davis Professor of Enology, Department of Viticulture and Enology is a leading expert on wine quality. He talked about varietal aromas and retaining specific flavors of grape in the wine. But as wine oxidizes, those aroma compounds can be lost. “Oxidation can be divided in two basic steps, quinone formation from polyphenols and aldehyde formation, all of which causes a loss in flavor,” said Waterhouse.

“Sulfites are widely used to prevent oxidation by reacting with quinone.

Tannins in red wine are also important as they react with quinone, thus removing oxidation from wine,” Waterhouse noted.

Waterhouse noted that the industry is also working with ascorbic acid and glutathione because both could be useful in reducing oxidation.