Evaluation of the Viticultural Performance of Newly Released Nematode Resistant Rootstocks in San Joaquin Valley Wine Grape Vineyards

As microscopic plant parasites, nematodes can cause extensive damage to grape vineyards. As the nematodes feed on and damage root cells, vine health, vigor, and productivity will decline. Nematodes affect many regions of California, but vineyards within the San Joaquin Valley (SJV) are particularly vulnerable to nematode damage due to typically sandy soil profiles and the wide range of parasitic nematode species found within the region, coupled with many soils being in agricultural production for decades. Traditionally, fumigation has been a viable method to provide relief from nematode pressur, but the California Department of Pesticide Regulation continues to regulate the volatile organic compound (VOC) emissions from field fumigants and fumigation is increasingly unavailable to growers with properties near schools or housing. Grape growers must begin to consider ways to reduce or eliminate the need to fumigate in order to keep up with regulations, but still ensure that nematode damage does not diminish the economic viability of their grape production. Rootstocks can provide a non-chemical alternative to resist soil pests like nematodes and maintain vine productivity. In recent years, several rootstocks have been released for commercial production including two USDA-ARS selections developed by David Ramming and Michael McKenry, RS-3 and RS-9, and the “GRN” series by Andrew Walker. Extensive work has examined nematode parasitism and sources of grape rootstock resistance, but how these rootstocks will perform with regards to viticultural characteristics in commercial plantings is still largely unknown. To promote the use of these new nematode resistant releases and see grape growers benefit from the years of research that went into developing these rootstocks, as well as be protected from increasing VOC emission regulation and economically damaging nematode pressure over time, field-based data on how these recent nematode resistant rootstock releases effect vine growth, yields, and fruit characteristics in commercial scale production is needed. In this study, on established trial site in a commercial high-wire, mechanically pruned Petit Verdot vineyard has consistently shown that Freedom generated the highest yields, but GRN4 also produces high yields. Freedom and the GRN selections generated significantly more growth than the comparatively weak performance of RS3, RS9, and 1103P at this site. 1103P was also under-ripe at the time of harvest, compared to the other selections. Seeing that several of the GRN selections were able to produce similar yields and fruit chemistry to Freedom, this indicates they may be a valuable tool for SJV grape growers to use when nematodes are a concern when planting. A second large-scale trial testing the GRN and RS selections was planted with Malbec in 2016, and will be evaluated as it matures. By using these two sites with a history of nematode pressure and managed under commercial growing conditions in non-fumigated fields, grape growers from around the SJV and all of California can benefit from the better understanding of how these rootstocks may effect vine vigor and berry maturation, and accordingly make the best choices to remain economically viable while using the best rootstocks available to resist nematodes.

Evaluation of New Winegrape Varieties for Warm Climate Viticulture in the San Joaquin Valley

Fifty six different red and white wine grape selections are being evaluated at the Kearney Agricultural Center, in Parlier, CA. These varieties were originally selected because they originate from warm-climate Mediterranean regions, and/or were believed to have traits that would be desirable in a warm climate wine region, like the San Joaquin Valley. Most of the selections were recently released to the industry from Foundation Plant Services and had not been previously evaluated in San Joaquin Valley or California. All vines are on 1103P rootstock, trained to bilateral cordons, and most were spur pruned. Beginning in 2013, certain varieties have also been subjected to simulated mechanical pruning. In 2016, the effect of not shoot-thinning some select varieties was evaluated. Grapes were harvested according sugar accumulation, with the harvest target for white varieties at 22° Brix, and reds at 25° Brix. At harvest, yield components, rot incidence, and basic juice chemistry were determined for all 56 varieties. The first harvest was on August 3, 2016 for whites (Petit Manseng) and August 12, 2016 for the reds (Ederena, spur and mechanical pruning). Harvest dates were similar or slightly later than the historically early 2014 and 2015 seasons. Total yields were lower than previous years for almost every variety. Yields for the spur pruned, shoot-thinned standard treatment ranged from 6.54 kg/vine (Carmenere) to 32.14 kg/vine (St. Emillion). Given the repeatedly delayed ripening, poor color accumulation, and lack of adaptability to mechanical pruning, Caladoc, Corvina Veronese, and Counoise are not recommended for the SJV. Segalin, a darkly pigmented variety that looks promising, responded well when not shoot thinned in the spring, while the white varieties had a range of responses to the lack of shoot thinning. These differences in response to more minimal canopy management offer insight into how these varieties may need to be managed in a commercial setting. For the mimicked mechanical pruning selections, yields were only sometimes greater than their hand pruned counterparts, since the greater, smaller clusters also tended to exhibit worse raisining and have smaller berries that reduce yields. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Petit Manseng is the most acidic, which consistently measures >10g/L titratable acidity in this trial every year, but other high acid white varieties include Arinto, Falanghina, and Fiano. Clonal selections of Charbono and Teroldego were grafted in 2014 and used to make wine in 2016. Differences in rot incidence, and ripening are more predominate in the Charbono selections, whereas the Teroldego clones are more similar to one another. Among the reds, these clonal selections, Morastell, Sagrantino, and Segalin consistently produces reasonable yields under deficit irrigation while producing high levels of desirable color and flavor compounds. From the work done in previous years, the most promising varieties continue to be narrowed down and some were made into wine at Constellation Brand’s experimental winery and the UC Davis teaching winery, which provides enological information and valuable extension opportunities in the future. The final juice chemistry and finished wines will be evaluated and presented during 2017. Four new selections were grafted over into more-promising selections at the start of 2016 (Assyrtiko, Nero d’Avola, Grand Noir, and Petit Bouschet). Extensive extension and outreach efforts have been made to promote this work, including being published in trade magazines and local newspapers, giving extensions, and hosting an educational wine tasting and field day.

Evaluation of Wine Grape Clones and Cultivars for the San Joaquin Valley

The performance of ten recently introduced selections of Syrah from Australia and France were evaluated at the Kearney Agricultural Center, Parlier, California. Variables measured included yield, yield components, fruit composition, and susceptibility to sour rot. There was considerable variation between some of the Australian and French Syrah selections. The Australian Shiraz selections 01, 03, and 07 have generally had higher soluble solids, higher pH, smaller berries, smaller clusters, and less sour rot than the French Syrah selections. Shiraz 1 is particularly early, and thus has the highest soluble solids, and among the highest pH and lowest titratable acidity, of the clones tested. Of the French selections, Syrah 525 was notable in having relatively low yields of small, compact, clusters which were highly susceptible to rot. Though production of grapes for high quality table wines is increasingly important in the San Joaquin Valley, there remains a market for generic white wine grapes, for concentrate, brandy, and generic wines and blends. To insure profitability of this commodity, growers must develop vineyards capable of producing high yields of fruit at low cost. To aid these efforts, four white winegrape varieties having high yield potential, Colombard, Grenache blanc, Triplett blanc, and 182-4 were compared when subjected to standard hand pruning, and simulated mechanical box pruning. The fruits of hand pruned Grenache blanc have generally attained 21 Brix in late August, one to two weeks ahead of the other varieties. Machine pruning delayed maturation of most varieties by at least one to two weeks, depending on the variety and year. Hand pruned vines, regardless of variety, averaged about 31.5 kg fruit/vine; machine pruning increased yields by 20{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} to 40{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}, depending on the year and variety. Machine pruning greatly increased the number of clusters per vine, but the clusters on machine pruned vines had fewer and smaller berries, and thus were far less susceptible to sour rot than the clusters of hand pruned vines. Thus, machine pruning increased yield and improved fruit quality compared to hand pruning, but it also delayed harvest, sometimes by several weeks, which may be undesirable.

Evaluation of Wine Grape Clones and Cultivars for the San Joaquin Valley

Two studies were conducted. In the first study, the viticultural characteristics, yield, and fruit quality of ten Syrah grapevine selections from Foundation Plant Services, UC Davis, were evaluated in a replicated trial at the Kearney Agricultural Center, Parlier, CA, a warm climate region. Having completed five harvests, it is evident that there is considerable variation between the Australian and French Syrah clones. As a group, the Australian Shiraz selections 01, 03, and 07, have ripened sooner than the French selections, as evidenced by their higher juice soluble solids and lower pH when harvested on the same date. The Australian selections also tended to have smaller berries, smaller clusters, and were much less susceptible to sour rot than the French Syrah selections, especially Syrah 525. Shiraz 01, 03, and 07 had yields which were similar to or less than that of many of the other selections, but they were also more vigorous than the others so yields of the Shiraz selections might be improved by retaining more nodes after pruning. In a second study, white winegrape varieties having high yield potential, Colombard, Grenache blanc, Triplett blanc, and 182-4 were compared when subjected to traditional spur pruning, and simulated mechanical box pruning. Over the first three years of the study, the fruits of spur pruned Grenache blanc have attained 21 Brix by the second or third week of August, a week or two ahead of the other varieties. Vines subjected to simulated machine pruning ripened one to two weeks later than spur pruned vines. Spur pruned vines, regardless of variety, averaged about 31 kg fruit/vine; machine pruning increased yields by 20{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} to 30{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}. Machine pruning greatly increased the number of clusters per vine, but the clusters on machine pruned vines had fewer and smaller berries, and thus were far less susceptible to sour rot than the clusters of hand pruned vines. Thus, machine pruning increased yield and improved fruit quality compared to hand pruning, but it also delayed harvest by about one week, which may be undesirable. An additional year of data is desired to bolster the preliminary observations of the second study.

Clonal testing of winegrapes in the San Joaquin Valley

Syrah grapevines may produce good to excellent quality fruit for red wine in the San Joaquin Valley so this variety may elevate the reputation of valley winegrapes if care is taken to maximize fruit quality. To help ensure optimal fruit quality and yield, growers should select the clone or clones that are best suited to the Valley’s climate. Many new selections of Syrah have recently been made available from Australia and France, but their relative performance in the San Joaquin Valley is not yet known. Thus, we are comparing the yield, yield components, fruit composition, and susceptibility to sour rot, of ten selections of Syrah in a trial at the Kearney Agricultural Center, Parlier. After three years, it is evident that there is considerable variation between the Australian and French Syrah clones. As a group, the Australian Shiraz selections 01, 03, and 07 have generally had higher soluble solids, lower pH, smaller berries, smaller clusters, and less sour rot than the French Syrah selections. Shiraz 1 is particularly distinctive in that its fruits are consistently the earliest maturing, having the highest soluble solids, and among the highest pH and lowest titratable acidity, of the clones tested.

Though production of grapes for high quality table wines is increasingly important in the San Joaquin Valley, there remains a market for generic white wine grapes, for concentrate, brandy, and generic wines and blends. To insure profitability of this commodity, growers must develop vineyards capable of producing high yields of fruit at low cost. To aid these efforts, four white winegrape varieties having high yield potential, Colombard, Grenache Blanc, Triplett Blanc, and 182-4 were compared when subjected to standard hand pruning, and simulated mechanical box pruning. In 2008, Grenache Blanc reached 21 Brix by 31 August, followed by 182-4 on 6 September, Triplett Blanc on 13 September, and Colombard on 14th September. All varieties had similar yields, about 35 kg (77 lbs) per vine, but Grenache Blanc was more susceptible to rot than Triplett Blanc or Colombard. Machine pruned vines produced about 20{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} greater yield than hand pruned vines, regardless of the variety. The clusters on machine pruned vines had fewer and smaller berries, and were far less susceptible to sour rot than the clusters of hand pruned vines. Thus, machine pruning increased yield and improved fruit quality compared to hand pruning, but it also delayed harvest by about one week, which may be undesirable. Additional data are needed to bolster these preliminary observations.

Improving Yield and Quality of Sauvignon Blanc

Clonal Trial: During the 2008 growing season, a trial containing 12 clones of Sauvignon blanc were grown and harvested. The vineyard is farmed organically, drip irrigated and planted in a Russian River loam soil in Hopland, Mendocino County, California. Clones include: UC FPS# 1, 6, 7, 14, 18, 20, 23, 25, 26, 27, 28 and 29. The experimental design is a ANOVA Randomized Complete Block with 8 replications of 5 vine vines planted in 4 long east/west rows. Replications are clearly marked with plastic cattle ear tags at the beginning and end of the plot containing the replication number and clone for easy identification. This is the second bearing year of the vineyard, and the vines were trained with two canes containing an average of 8 buds per cane on a vertical shoot positioned trellis (VSP). Vines were managed during the growing season to the cooperating grower’s commercial standards including trunk and cordon suckering and removal of sterile shoots, positioning shoots upright inside of fruiting wires, and a standard powdery mildew program utilizing stylet oil and wettable sulfur pre-bloom, and sulfur dust post bloom. No insecticides or miticides were applied. Not all vines are bearing at commercial levels, but we were able to sufficiently harvest enough fruit to make valid mean comparisons.

Harvest occurred on September 8th scheduled to coincide with other Sauvignon blanc being crushed by the cooperator. Target fruit maturity was 22.5 to 23.5 {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} brix. Following are the data: See tables on progress report.

Clonal Testing of Winegrapes in the San Joaquin Valley

Syrah grapevines may produce good to excellent quality fruit for red wine in the San
Joaquin Valley so this variety may elevate the reputation of valley winegrapes if care is
taken to maximize fruit quality. To help ensure optimal fruit quality and yield, growers
should select the clone or clones that are best suited to the Valley?s climate. Many new
selections of Syrah have recently been made available from Australia and France, but
their relative performance in the San Joaquin Valley is not yet known. Thus, we are
comparing the yield, yield components, fruit composition, and susceptibility to sour rot,
of ten selections of Syrah in a trial at the Kearney Agricultural Center, Parlier. After two
years, it is evident that there is considerable variation among the Syrah clones. The fruits
of clone 1 are the earliest to mature; at harvest their fruit have the highest soluble solids,
and among the highest pH and lowest titratable acidity, of the clones tested. In contrast,
fruits of clones 100, 174, 300, and 525 had the lowest soluble solids of the clones tested,
though the pH and TA of their juices was similar to that of many other clones. Clones 03
and 100 produced 15 to 35{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} greater yields than the other selections because they had the
most, and among the heaviest, clusters of fruit. Clones 03 and 100 were moderately
susceptible to sour rot, having higher sour rot incidence than Shiraz 01, Shiraz 03, Shiraz
07, and Syrah 99. Syrah 525 had far higher sour rot incidence than the others perhaps, in
part, due to its high number of berries per cluster. Clone 99, in this early stage of
evaluation, is one of the most promising selections because it has relatively good yields,
is somewhat resistant to sour rot, and has fruit composition that is comparable to that of
many other clones. Though production of grapes for high quality table wines is
increasingly important in the San Joaquin Valley, there remains a market for generic
white wine grapes, for concentrate, brandy, and generic wines and blends. To insure
profitability of this commodity, growers must develop vineyards capable of producing
high yields of fruit at low cost. To aid these efforts, four white winegrape varieties
having high yield potential, Colombard, Grenache Blanc, Triplett Blanc, and 182-4 were
compared. Colombard and Grenache Blanc matured about three weeks earlier than
Triplett Blanc and 182-4, with similar yield and fruit composition at harvest. However,
Colombard is much more susceptible to sour rot than Grenache Blanc, or Triplett Blanc.
All things considered, Grenache Blanc was superior to the other varieties due to its
earliness and lower susceptibility to sour rot.

Evaluation of Cabernet Sauvignon Clones: Heritage, French and Old California Sources

Yield and yield components and juice chemistry data were taken on 15 clones of Cabernet Sauvignon, comprised of five long-held selections from UC Davis Foundation Plant Services, our newer selections arriving from California or as importations from Italy and France, and three California ?Heritage? selections. Also planted in the experiment were the three Heritage clones with their original virus infections, to be contrasted with their now-available clean counterparts.

Second year data were taken in 2006 showed similar trends to the 2005 data with significant differences in vine yield components among clones. One Italian selection (FPS 27), one Heritage selection (FPS 29-Niebaum Coppola) and the French selection (ENTAV 169) respond more like high-yielding FPS 14 (Chile). In contrast, the new California selection (FPS 24), second Italian selection (FPS 26) and Heritage selection FPS 30 (Disney Silverado) were more like moderate yielding selections FPS 2 and 4. The third Heritage selection (Mondavi To-Kalon) was the most interesting new selection in that it yielded the lowest, slightly lower than low yield standard FPS 6.

Virus-infected selections contrasted with their clean counterparts showed significant yield reductions in two comparisons, while in the third it was a small difference. However, all virusinfected selections, despite already having lower yields, were severely delayed in ripening. The difference in ripening was as much as 4 Brix lower in diseased materials. These of new materials are ready for winemaking in 2007.

One important outcome of the trial in 2006 was the appearance of virus-like symptoms (red leaves) in healthy vine treatments adjacent to virus treatments. Evidence is mounting in Napa that LR virus is spreading, likely as a result of the feeding activity of mealybugs. Obviously, a comparison of infected and healthy treatments is valuable only if the healthy vines remain so. The apparent movement of virus jeopardizes all of the remaining healthy clones not just the virus vs non-virus comparisons. Because this risk is great, and the data comparing virus and healthy is sufficient to draw conclusions, the virus-infected treatments will be removed in late winter 2007.

Evaluation of Zinfandel Heritage Selections

No evaluation of the Heritage selections can be made while comparing selections of unknown virus status. Relying on visual inspections every effort was made to take selections that were free of virus. We knew, however, that tests would have to be made to confirm the virus status of the selections. Initial steps were taken toward understanding virus status of the selections very early in the history of the Heritage Vineyard.

In 1991 Dr. Deborah Golino and FPMS took 3 selections for woody indexing of virus. In 1997 six more selection went to FPMS for woody indexing. In 1999 all the selections in phase I and II were surveyed for virus using polymerase chain reaction (PCR) at FPMS.

Selections 4, 5 and 6 were indexed beginning in 1991. They were found by woody indexing to be free of virus exclusive of grapevine rupestris stem pitting associated virus (RSP), which two had. This was not surprising since we know that vines grafted on St. George rootstock are almost always infected with RSP. The two selections testing positive for RSP are now in the process of having the virus removed by shoot tip culture. Tests should be complete this year and results will be reported in next year?s report.
Selections 10, 25, 46, 53, 60 and 61 were delivered to FPMS in 1997 for woody indexing. In addition to RSP that 5 selections had, 4 had grapevine leafroll associated virus (GLR) and one tested positive for grapevine fanleaf virus (GFLV). The selection with GFLV was immediately removed from the vineyard. All of these selections, including the GFLV positive selection, are now in the process of having the virus removed by shoot tip culture.

The PCR testing completed in 1999 yielded mixed results, a complete table of results can be found in our report submitted in 2001. After discussion with Dr. Golino we have decided not to consider fleck as a damaging virus and have removed it from consideration. Polymerase chain reaction detection of virus in grapevines is now felt to be more sensitive than traditional woody indexing. For this reason beginning last year all new material coming into FPMS undergoes both PCR and woody indexing. It is important to this project to note that the three selections that underwent woody indexing for virus were all found to be free of GLR. The PCR test however, found all three to be infected with GLR 4,5 complex. From this point forward, we will use PCR as the definitive virus test for this project. Of the viruses tested for GLR was by far the most common with 46{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the selections infected with one or more of the GLR complexes. Interestingly, only one selection that was free of GLR was found to have one of the other viruses. The number of selections testing positive for GLR was not anticipated, teaching us once again that the lack of red leaves in fall is far from being assuring a negative virus status.

Dr. Golino has performed these tests free of charge for the project and we are indebted to her and FPMS for their cooperation and support. Only selections that are free of virus (not including Fleck or RSP) will be considered for a replicated trial of these selections and further data collected will be presented indicating virus status. In 1998 we began viticultural evaluations of the selections in Phase 1. These measurements are taken at harvest and include °Brix, pH, TA, berry weight, yield per vine, cluster weight, cluster number and pruning weight per vine. Collection of yield per vine and clusters per vine did not begin until 1999.

PDF: Evaluation of Zinfandel Heritage Selections

Evaluation of Winegrape Clones

This project evaluates 20 Pinot noir and 13 Chardonnay clones for their viticultural and enological attributes in production of base wines for sparkling wine production and five Merlot clones for their viticultural and enological attributes for production of red wine. Replicated plots of Pinot noir and Chardonnay clones have been established at Gloria Ferrer in Sonoma and of Merlot at the Department?s Oakville Experimental Vineyard.

Chardonnay mean harvest °Brix was 21.1 in 2001. Yield in 2001 was consistent with the four-year averages. Clone 4 and the Wente clone had the highest and lowest yields respectively. The yield range was approximately 2x for the four-year data and in 2001. The Wente clone has had the lowest yield in each year of the trial and in both 2001 and the four-year data the Wente clone stands out as for its extremely low yield. The four-year mean data show differences in yield were driven by cluster weight through both berries per cluster and berry weight. Clone 4 had heavier clusters due to significantly more berries per cluster. The Wente clone had both the fewest berries per cluster and the lightest clusters. Interestingly, the clone 4 clusters were large enough to make up for the fact that it had the fewest number of clusters in 2001 and in the four-year data.

In Pinot noir, as with the Chardonnay clones, harvest was determined on a Brix basis. Yield ranged from 5.3 (clone 13) to 8.7 (clone 13) kg vine-1 for the three-year data. The data showed significant differences for all yield parameters. While no one yield parameter (Fig. 5) can be shown to be the driving force of yield differences, cluster number is the best correlated. Clusters per shoot on the other hand varied by clone from 1.5 to 2.2 and did have a significant correlation to yield (r = 0.59). Cluster berry number was also positively and significantly correlated to yield.

As in preceding years, Merlot clone FPMS 8 had the lowest yield (6.3 tons/acre) in the 2000 growing season compared to the other clones (9.2 to 10.3 tons/acre). The primary contributing yield component was berries per cluster (103 for clone FPMS 8 versus 151 to 164 for clones 1, 3, 6, 9) this was also consistent with past data. In 2000 clone FPMS 8 produced the smallest berries and second lowest number of clusters per shoot. Averaged over six years, clone FPMS 8 has produced approximately two thirds the yield of the other four clones due to smaller clusters caused by reductions in both number of berries per cluster and berry size.

PDF: Evaluation of Winegrape Clones