Vineyard Air Temperature Profiles and Their Implications for Vine Training Decisions

This project evaluated how air temperatures vary with height above the ground surface throughout the growing season at various vineyard areas representative of the diverse Central Coast region. The purpose of this project was to identify if useful stratification in temperatures occurred at the study sites, and to quantify the potential benefits that could be attained by using alternative vine training heights to reduce potential frost risk and/or to avoid excessive summertime temperatures. The fundamental hypothesis of this effort has been that taller vine training heights may bring useful benefits in some areas, and that this type of detailed temperature analysis will help identify those areas and help to predict what benefits may be obtained with any changes in vine training height.

The 2013 season measurements at seven sites in San Luis Obispo and Santa Barbara Counties proceeded as planned, however with an equipment malfunction resulting in only partial season data at one site in Shandon. Temperatures were measured at one-foot intervals above the ground surface between 1 ft. and 8 ft. heights, using precision data loggers taking high-frequency measurements. Some sites demonstrated useful increases in temperature with increasing height above the ground surface on cold spring nights, but this pattern was not observed everywhere. In the most extreme example, the temperature gain at 8 ft. elevation was 9 °F warmer than at 1 ft. elevation; such stratification would have very positive benefits for frost protection. Other sites showed little similar stratification, likely due to air movement during the night.

At all sites the cumulative degree days over the April 1 – October 31 growing period tended to decrease with increasing height above the ground. This indicates the potential that taller vine training heights may have for addressing some of the gradual increases in degree days that have been occurring in recent decades, and which are forecast to continue increasing with climate change.

In 2014, detailed measurements are being conducted with multiple stations at two properties, to determine how variable the temperature profile characteristics can be at individual sites. The assessment of temperature profiles over different ground cover conditions was not conducted as planned due to insufficient cover crop conditions; this will be addressed at a later date.

Evaluation of new Winegrape Varieties for the San Joaquin Valley

A wine grape variety trial was established in 2008 at the Kearney Research and Extension Center, a warm climate region. The trial consists of 55 16-vine plots, each planted to a different red or white wine grape selection originating from warm-climate Mediterranean regions, and/or believed to have traits that would be desirable in a warm climate wine region. Most of the selections tested were recently released to the industry from Foundation Plant Services so, in many cases, certified selections have never been evaluated in California. All vines are on 1103P rootstock and in 2011 and 2012, the first two cropping years, all vines were spur pruned, leaving 8 or 9 two-bud spurs per meter of cordon; in 2013, certain varieties were subjected to simulated machine pruning, or cane pruning.

In general, we attempted to harvest all white varieties at 22 Brix, and reds at 24 Brix, but certain selections were picked at higher or lower Brix depending on a number of factors, including the desired wine style. At harvest, yield components, rot incidence, and basic chemistry were determined and wine lots were made at Constellation Brand’s experimental winery. The varieties were harvested across a wide range of dates starting with a white cultivar, Fiano, in early August, and ending with about a half dozen red and white varieties that were harvested on the last day of October. Yields ranged from less than 6 kg per vine for Prieto Picudo to more than 50 kg of fruit per vine from the machine-pruned Tocai fruliano, a white cultivar. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Berries from red varieties also varied widely in their content of anthocyanins, tannins, and other phenolic compounds.

Most varieties had slightly higher anthocyanin content in 2013 than they did in 2012, and Bonarda and Segalin noir have consistently had the highest anthocyanin content of the varieties tested. Wines from the trial will be made available for tasting and analysis in 2014, as they have been in each of the past several years. Twelve varieties which performed very poorly in 2011 and 2012 were topworked to new selections in 2013, and some varieties were subjected to different canopy management practices to determine if yield and rot problems could be ameliorated. Shoot tucking generally had little if any affect on fruit quality or rot, but simulated machine pruning greatly increased yields and reduced rot of most varieties subjected to this practice. Additional years of data are needed to determine if the high yields of machine-pruned vines are sustainable and whether or not they adversely affect fruit or wine quality.

Defining Crop Load Metrics for Quality Pinot Noir Production in Oregon

A three year study began in 2013 to determine the impact of varying crop levels on vine growth and vine balance. The project involves two components: 1) development of a large grower collaborator crop load study and 2) monitoring of vine growth, nutrition and physiology measures within four sites from the larger study. During 2013, the project included a total of 13 vineyard and winery businesses from across six AVAs in the Willamette Valley of Oregon. Collaborators successfully completed their first season of data collection as of this reporting, and results are being compiled and analyzed in winter 2014. The additional data from the four sites within the study are being analyzed in winter 2014, but preliminary data that shows no difference in vine photosynethetic assimilation or vine nutrition at bloom or véraison when comparing full crop (non-thinned vines) with those thinned to one cluster/shoot.

Water Footprint, Productivity and Drought Responses of Seventeen Wine grape Cultivars in the San Joaquin Valley

This research focuses on the adaptation and drought responses in yield and fruit and wine quality of seventeen, red wine grape cultivars. The project exploits an established variety trial in which the cultivars were selected for potential adaptation to San Joaquin Valley conditions and by doing so extend the information derived from the previous investment to establish this experimental vineyard – used by Dr. Jim Wolpert from 2006 to 2010. Reducing the plant-available water (by restricting irrigation) can be expected to reduce yield, but to also increase water use efficiency and fruit quality of red wine grapes. The timing of water deficits affects many of the vine responses to stress and the resulting wine sensory characteristics. For example, early(preveraison) deficits have a greater effect on tannins than late deficits, whereas for anthocyanins(color) it is the reverse. The studies that have established these phenomena were conducted in moderate (North Coast) climates and with common cultivars such as Merlot, Cabernet Sauvignon and Cabernet franc. This study will test whether those observations hold in the warmer San Joaquin Valley across numerous cultivars.

Estimated ETc from budbreak to average date of harvest across cultivars and irrigation treatments (end of August) was 619 mm (24.4 in). Applied water to vines irrigated at full ET from budbreak  to veraison after which the irrigation was terminated (I ? Ni treatment), applied water at 50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of estimated ETc season long (0.5 ETc treatment) and no applied water up to veraison and then applications thereafter at 50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of ETc (Ni ? 0.5) were 397, 347 – 453 and 173 – 293 mm,  respectively. The effect of irrigation treatment on vine water status (midday leaf water potential) similarly affected all cultivars.

Early water deficits (no applied water up to veraison; Ni ? 0.5 treatment) greatly reduced berry weight at veraison and harvest compared to the other two irrigation treatments across cultivars. The no applied water after veraison treatment (I ? Ni) reduced berry weight of 13 cultivars at harvest compared to their veraison berry weight. Titratable acidity (TA) in the berries of 15 of the cultivars at harvest was greater for the I ? Ni treatment compared to the other two irrigation treatments (the exceptions were Tinta Amarella and Tinta Madeira). The greatest TA values across irrigation treatments were for Durif, Cabernet Sauvignon and Tannat. Berries and the wines made last year are currently being analyzed for color, phenols and tannins.

Use of Surface Renewal to Detect Water Stress-Induced Changes In Daily Water Requirements in Vineyards Subjected to Deficit Irrigation

Deficit irrigation has evolved as a tool to reduce water use in viticulture because of increasing water scarcity in many agricultural regions. The accomplishment of this objective depends on the accurate knowledge of both vineyard water requirements and vine water status. The improved surface renewal method (SR) is a bio-meteorological technique that can be used to accurately measure crop evapotranspiration (ETa) at a vineyard scale. A deficit irrigation experiment was carried out in a commercial vineyard of the North Coast Viticultural Region, CA.

The objective of the study was to determine the impact of irrigation practices on the relationships of SR estimates of ETa and vine water status parameters, such as leaf water potential (ΨLEAF) and stomatal conductance (gs). Three irrigation treatments were applied from veraison to harvest: Wet Control: vines were irrigated at 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} ETc (as calculated by Williams & Ayars, 2005); Medium-Wet: vines were irrigated between 70-80{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} ETc; Moderate Deficit: vines were irrigated between 40-50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} ETc. SR provided with reliable estimates of daily ETa compared to the eddy covariance, which is regarded as the reference bio-meteorological method for measuring ETa.

Although ΨLEAF was consistently higher in the wet control than in medium-wet and moderate deficit treatments, the medium-wet block showed the highest ETa and gs values. Surprisingly, vines from the wet and the moderate deficit treatments often exhibited similar ETa values, regardless of large differences in applied water and ΨLEAF. A quadratic relationship between ETa/ETo and ΨLEAF indicated that the maximum water demand was reached at mild levels of water stress (~0.9 MPa). Conversely, vines under wet (>-0.7 MPa) or severe water stress (<-1.4 MPa) conditions showed similar ETa/ETo values. These results showed that the SR technique can be used to better understand the extent of the effect of irrigation practices on both vineyard water use and vine water status in winegrape production.

Use of Surface Renewal to Detect Water-Stress-Induced with Changes in DailyWater Requirements in Vineyards Subjected to Deficit Irrigation

Deficit irrigation has evolved as a tool to reduce water use in viticulture because of increasing water scarcity in many agricultural regions. The accomplishment of this objective depends on the accurate knowledge of both vineyard water requirements and vine water status. The improved surface renewal method (SR) is a bio-meteorological technique that can be used to accurately measure crop evapotranspiration (ETa) at a vineyard scale. A deficit irrigation experiment was carried out in a commercial vineyard of the North Coast Viticultural Region, CA. The objective of the study was to determine the impact of irrigation practices on the relationships of SR estimates of ETa and vine water status parameters, such as leaf water potential (ΨLEAF) and stomatal conductance (gs). Three irrigation treatments were applied from veraison to harvest: Wet Control: vines were irrigated at 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} ETc (as calculated by Williams & Ayars, 2005); Medium-Wet: vines were irrigated between 70-80{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} ETc; Moderate Deficit: vines were irrigated between 40-50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} ETc. SR provided with reliable estimates of daily ETa compared to the eddy covariance, which is regarded as the reference bio-meteorological method for measuring ETa. Although ΨLEAF was consistently higher in the wet control than in medium-wet and moderate deficit treatments, the medium-wet block showed the highest ETa and gs values. Surprisingly, vines from the wet and the moderate deficit treatments often exhibited similar ETa values, regardless of large differences in applied water and ΨLEAF. A quadratic relationship between ETa/ETo and ΨLEAF indicated that the maximum water demand was reached at mild levels of water stress (~0.9 MPa). Conversely, vines under wet (>-0.7 MPa) or severe water stress (<-1.4 MPa) conditions showed similar ETa/ETo values. These results showed that the SR technique can be used to better understand the extent of the effect of irrigation practices on both vineyard water use and vine water status in winegrape production.

An Assessment of Wind Machine Performance for Vineyard Frost Protection

This 2012 project evaluated temperature changes resulting from wind machine operation for both upward-blowing wind machines and conventional horizontal-blowing machines. Measurements were conducted at dozens of locations in commercial vineyards throughout the counties of Santa Barbara, San Luis Obispo, Sonoma and Mendocino.

The study relied almost entirely on wind machines which had been previously installed by vineyard operations for their own frost protection needs, and which were operated by the cooperators during the study period whenever they felt that frost protection was needed. Instrumentation was installed at 34 wind machines; not all sites experienced frost conditions, but machines were operated sufficiently at 29 of the 34 sites. These included 22 sites with upward-blowing wind machines and seven sites with conventional machines. We compared the observed air temperatures at distances of 15, 30 and 60 m from each wind machine, compared to the predicted temperature values if the wind machines had not been operated.

Overall, the operation of the conventional wind machines showed useful temperature increases which were similar to results from previous studies, while the operation of the upward blowing wind machines had minimal effect on increasing air temperatures. Additional detailed studies were conducted with a medium-sized upward-blowing wind machine at a future vineyard site. Comprehensive temperature measurements were made using 52 sensors surrounding the machine in all directions, over 12 operation nights. Little or no temperature gains were observed from the operation of this machine under the particular conditions of the study.

Improved information on the relative benefits of different types of wind machines and their ability to alter vineyard temperatures is important for vineyard operations that require some form of frost protection. As water supplies for sprinkler frost protection become more limited, there is increasing attention being paid to wind machines as a potential alternative in many areas. This study will provide growers with useful information to help them to make the most informed frost protection decisions possible.

Update of the Paso Robles Soil Salinity Survey

This 2012 project completed the fourth repeat sampling of soils at vineyards in the Paso Robles Groundwater Basin area. These vineyards are irrigated with groundwater of varying quality, leading to the potential for soil salinity levels to increase over time. Elevated soil salinity conditions will in turn lead to degraded soil quality and reduced vine growth and production. The information on soil salinity levels and trends resulting from this study will enable growers to design vineyards and manage the soil and water to ensure long term sustainable production.

The initial sampling was carried out in 2006 at 100 vineyard sites in the area east of Paso Robles; sampling at the same locations was repeated in 2007, 2009 and 2012. The results have shown a clear trend for increasing levels of the soil electrical conductivity and the soil sodium content; these two factors are the primary salinity parameters of concern in the region. Increases in the soil electrical conductivity imposes additional water stress on the vineyards, and higher soil sodium content leads to degraded soil physical quality with important implications for reducing desirable soil drainage and aeration conditions. The average soil electrical conductivity in 2012 was 3.09 dS/m, which is greater than the standard damage threshold value for sensitive vine rootstocks.

The main salinity toxicity component of concern in the area is boron; this was assessed only in 2009 and 2012, and showed a slight increase over this period. The 2012, over 20{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the sites had soil boron levels that exceeded the standard grapevine damage tolerance range of 0.5-0.75 mg/L. There is concern that boron levels in the groundwater may increase as water levels in the aquifer decline and increased mixing of lower-quality water from deeper in the groundwater basin occurs; thus establishing baseline boron levels will help gauge any such changes over time.

This project has provided an important evaluation of fundamental soil salinity conditions over a broad region, and has identified important trends of interest to the local grape industry. These types of conditions are not unique to the Paso Robles area; other regions of the Central Coast will also have similar conditions due to the use of marginal quality groundwater for irrigation and the lack of effective natural leaching by rainfall. Prudent vineyard managers will assess water and soil salinity factors prior to planting, will choose appropriate rootstocks for the expected conditions, and will manage soil and water to reduce the potential for salinity levels to increase over time.

Evaluation of New Winegrape Varieties for the San Joaquin Valley

A wine grape variety trial was established at the Kearney Research and Extension Center, a warm climate region. The trial consists of 55 16-vine plots, each planted to a different red or white wine grape variety selected from warm-climate Mediterranean regions. Most of the varieties tested were recently released to the industry from Foundation Plant Services so, in many cases, certified selections of these varieties have never been evaluated in California. All vines were spur pruned, leaving 8 or 9 two-bud spurs per meter of cordon.

We attempted to harvest all white varieties at 22 Brix, and reds at 24 Brix, though inclement weather forced the harvest of a few slow ripening varieties in early November, before they were completely ripe. At harvest, yield components, rot incidence, and basic chemistry were determined and, for 25 of the 55 varieties, wine lots were made at Constellation Brand’s experimental winery.

The varieties were harvested across a wide range of dates starting with a white cultivar, ‘Fiano’, on 18 August, and ending with 15 red and white varieties which were harvested in the first week of November. Yields ranged from a meager 2.32 kg per vine from the red cultivar Carmenere, to more than 35 kg of fruit per vine from the white cultivar ‘Trebbiano Toscano’. Harvest date was poorly correlated with yield, but there was a relatively strong positive correlation between rot incidence and harvest date.

Yield of red and white varieties was more strongly correlated with cluster weight than with the number of clusters per vine, and cluster weight was more strongly correlated with the number of berries per cluster than with berry weight. Red and white varieties varied widely with respect to pH and titratable acidity. Other fruit composition data were collected by Constellation and will be shared in a future report. Wines from the trial will be made available for tasting and analysis in 2012.

Evaluating the Role of Excess Levels of Nitrogenous Compounds, Including Amino Acids and Putrescine, in the Occurrence of Pinot Leaf Curl

The objectives to investigate the relationship between elevated ammonium and glutamine levels in grape leaves exhibiting Pinot Leaf Curl and to compare the levels of putrescine in symptomatic and asymptomatic leaves were completed.  Ammonium and glutamine varied widely among leaf samples and in many instances leaves with symptoms showed elevated levels of these metabolites compared to leaves without symptoms. However, examples where the levels of glutamine and ammonia were nearly equal were found and in some cases symptom leaves actually exhibited lower levels of these compounds than non-symptom leaves.

While the levels of ammonia and glutamine are certainly of interest in assessing the nitrogen status of grapevine leaves, they do not show promise as markers or indicators of Pinot Leaf Curl. On the other hand, the diamine putrescine (1,4-diaminobutane) was found to be elevated in 12 of 14 cases studied in this project, and in the other two the levels were the same in symptom and non-symptom leaves. Therefore, unlike glutamine and ammonia, no examples were found where putrescine was higher in non-symptom leaves than in symptom leaves.

Since putrescine has been implicated as a toxic metabolite leading to leaf chlorosis and necrosis in potassium deficiency and Spring Fever this research suggests the possibility that it also plays a role in Pinot Leaf Curl. However, given the range of putrescine observed in symptom and non-symptom leaves from various Pinot varieties and clones from different sites, its presence remains correlative relative to symptoms and a causal role remains to be established.

The success of this research lies in the fact that prior to this study we had only anecdotal evidence that Pinot Leaf Curl is a nitrogen-related disorder. The differences seen in all of the nitrogen metabolites studied in this project, especially putrescine, give some support to that idea and may suggest management practices that could be tried in an attempt to ameliorate the disorder.