The Latest in Wine and Grape Research

Davis, Calif.—Scientists gave 15-minute presentations about research they are conducting related to wine and winegrapes during a daylong conference recently at the University of California, Davis. The participating researchers received funding from one of the agencies that participate in the Unified Grant Management for Viticulture and Enology program (UGMVE). UGMVE director Dr. Deborah Golino, who is also director of the Foundation Plant Services at UC Davis, gave an update about the grapevine red blotch-associated virus at the service’s Classic Foundation Vineyard and the Russell Ranch Foundation vineyard. Red blotch, as it’s commonly known, has emerged only recently as a significant threat to vines and winemaking. It is widespread in some vineyards in Napa Valley and elsewhere. It manifests through red leaves that appear similar to those on vines with leafroll virus; infected vines don’t reach sugar levels expected in most modern winemaking (typically less than 22° Brix). Golino reported, however, that extensive testing has turned up only three infected vines at the Classic Foundation Vineyard out of about one-third tested, and none in the new Russell Ranch vineyard. Golino authored a comprehensive article about red blotch, which will run in the Practical Winery & Vineyard section of the April 2013 issue of Wines & Vines. Surprising discoveries Ken Shackel of UC Davis’ Department of Plant Sciences discussed grape cracking or splitting, which many winemakers and vineyard managers believe is caused by excess watering near harvest. Many growers reduce late-season irrigation to prevent this problem, which also may partially dehydrate grapes and increase sugar concentration. Surprisingly, Shackel discovered the reverse is true: The biggest cause of cracking is cutting back on water near harvest. “Deficit irrigation is a big cause of cracking,” he stated, offering news that may cause growers to rethink their irrigation programs. Mark Battany, UC extension advisor for San Luis Obispo and Santa Barbara counties, then gave an update about wind machine and temperature inversion studies. He evaluated both conventional wind machines and ones that blow upward and found that the conventional wind machines can provide increases of about 1°C, but that upward wind machines were less effective, at least at the site where he tested them. To many winemakers, the southern San Joaquin Valley seems an inappropriate place to grow Pinot Gris, even though it’s needed for very inexpensive wines. Kaan Kurtural of the Viticulture and Enology Research Center at California State University, Fresno, found that growers suffer low profit margins unless they get yields of 12 tons per acre and minimize vine labor. This calls for machine harvesting, naturally, but also mechanical pruning. Simply hedging the plants leaves too many buds or too many leaves, so the vines are out of balance. However, removing excess leaves isn’t worth the cost. Andy Walker of UC Davis talked about his grape rootstock breeding programs. Walker’s hybrid GRN-1 rootstock has high disease resistance since it’s half Vitis rotundfolia, the southern Muscadine family like Scuppernong, which has very high resistance to fanleaf virus as well as phylloxera. The hybrid is hard to propagate; rotundfolia has 39 chromosomes, and vinifera has 38, so most progeny are infertile. Research is also being conducted with inserting genes from resistant rootstocks into Thompson seedless and St. George vines. Unfortunately, new strains of phylloxera are evolving, reducing the usefulness of some existing rootstocks. Work is progressing in salt and drought-tolerant rootstocks as well as Pierce’s disease-resistant rootstocks. James Kennedy of CSU Fresno described work into the influence of grape and wine production practices on tannin extractability and activity. Specifically, the concentration of tannins doesn’t accurately reflect the resulting taste: Some tannins exhibit bitterness, others astringency. Cooler growing areas encourage astringency. The source of the tannins affect that quality; Kennedy is working on tools that would help growers predict the impact—or, as he put it, “help them deal with winemakers.” Peter Cousins, who is now at E. & J. Gallo, described his work breeding nematode-resistant rootstocks at the New York State Agricultural Experiment Station in Geneva, N.Y. Rootstocks like Harmony, Ramsey and Freedom were widely planted in the San Joaquin Valley of California. Though highly resistant to rootknot nematodes, the nematodes evolved reducing resistance. They developed new, resistant rootstocks called Matador, Minotaur and Kingfisher, all now available to nurseries for propagation. He noted that about half the grape varieties in the world are found in the new world, and they’re most likely to be resistant to phylloxera, but most don’t root well from cuttings, which is why they’re not used as rootstocks. Two speakers discussed trunk diseases. Philippe Rolshausen from UC Riverside talked about various synthetic and organic treatments as well as a new bee’s wax and pesticide compound. Sealing wax by itself isn’t enough. Also effective are sprayed Topsin and thiophanate methyl, which was most effective in trials. It can be machine sprayed to reduce disease and labor costs. Renaud Travadon of UC Davis described the biology and genetics of Phaeomoniella chlamydospora, one of the causal agents of Esca. It can be controlled by replacing vines, double pruning and protecting pruned wood. Mealybug findings Four sessions dealt with grape mealybug, the vector for leafrol l virus. Monica Cooper, extension advisor for Napa County, talked about the county’s program to control mealybugs in relation to grapevine leafroll disease, while Neil McRoberts of UC Davis described how modeling leafroll epidemics provides a means to facilitate discussion about the sustainability of the winegrape industry. One conclusion: The most important effort is to stop the spread between blocks; clean planting material doesn’t help much if it can be infected. Adib Rowhani of UC Davis discussed grapevine leafroll associated virus’s symptoms and effects on rootstocks, then Rodrigo Almeida from UC Berkeley completed the discussion of leafroll by describing mealybug transmission of the virus.

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