Evaluation of Mechanical Thinning to Improve Composition of Wines from Minimally Pruned and Machine Pruned Vineyards

The effect of different levels of mechanical thinning on growth, yield, fruit composition and wine quality of Cabernet Sauvignon grapevines was studied. Minimally and machine pruned vines were examined and compared against a bilateral cordon, spur-pruned control. Thinning treatments were performed on minimally pruned vines using a mechanical harvester equipped with bo-peep rods set at two head speeds. The moderate thinning treatment was achieved by a striker speed of 150 RPM and the severe thinning treatment by a speed of 200 RPM. Mechanically pruned vines were included in the experiment but were determined to not require crop thinning during the initial season of this study. Additionally, a minimally pruned, non-thinned treatment was studied. Wines were made from the four treatments and were evaluated for composition. Significant differences in growth and yield parameters were observed, however few significant differences were evident among treatments for fruit composition and wine quality. The preliminary results obtained through this study confirm that mechanical thinning may be used as a practical tool to control vineyard crop size. It should be noted that the timing and level at which the thinning practice is performed is of great importance to its effectiveness. Results obtained in 1996 suggest that minimal and machine pruning can produce fruit and wines that do not differ in composition from traditionally trained vines.

Evaluation of Trellis/Training Systems and Subsurface Drip Irrigation for Wine Grape Production in California

This study is being conducted in a 15 acre Sauvignon blanc vineyard located on the California State University, Fresno Agricultural Laboratory. The vines are grafted to Freedom rootstock and were planted on a spacing of 8′ x 12′ (vine x row) in 1992. Row direction is north to south with approximately 70 vines per row. The 1996 season represents the second year of data collection for this project. Deficit irrigation scheduling treatments were fully implemented and statistical differences due to treatment were observed. As in 1995, differences were again observed in the management of the irrigation systems. Use of subsurface drip irrigation allowed for reduced application of herbicides. One application of glyphosate to perennial weeds could be avoided because berms were dry. Conversely, use of subsurface drip irrigation required increased efforts for control of gophers. Significant training system effects on yield and fruit composition were observed in 1996. Yields were highest for the open lyre and minimal pruning treatments. Increased yield resulted from higher numbers of clusters per vine. There was an inverse relationship between yield and berry weight or cluster weight, although the number of berries per cluster was not affected. Fruit maturation was delayed significantly for the training systems which had the highest yields. Vines which were minimally pruned showed significantly lower levels of titratable acidity. Irrigation method also had a significant impact on yield and fruit composition in 1996. In general, as irrigation deficit increased, yield level decreased. The number of cluster per vine followed a similar pattern, indicating that this parameter was the most important factor involved in determining yield level. Differences in berry weight and the number of berries per cluster were not statistically significant. Statistically significant differences in soluble solids and pH were observed. Soluble solids were highest in 0.8 Et SDI and lowest in 0.8 Et AGD, even though the amount of water applied was identical for each. There was a trend for increased irrigation deficit to significantly increase pH in the fruit. Training system had a greater impact on vegetative growth than irrigation method during the 1996 season. Shoots per vine was significantly higher for minimally pruned vines. However, total vegetative growth, as indicated by mature nodes per vine, was greatest for GDC vines and lowest for MP vines. There were few treatment effects on vine water relations except at veraison when differences due to irrigation method were detected. Vines with the SDI 0.4 Et treatment had lower stomatal conductance than vines with the SDI 0.8 Et. At this point in the project, significant differences between training systems and irrigation methods have been detected. Further research is needed to determine the reasons for the observed differences.

Influence of Canopy Density on the Performance of Vertically Shoot Positioned Grapevines in the Central Coast

The purpose of this study is to examine the effects of leaf area density on the performance of vertically shoot positioned Chardonnay grapevines in coastal regions. The primary objective is to develop quantitative guidelines for optimum canopy density and vine performance for vertically shoot positioned canopies. The experiment was established in 1996 in a mature, vertically shoot-positioned Chardonnay vineyard located near Greenfield in the Salinas Valley. The vines are bilateral cordon trained and spur pruned. Primary shoot density was adjusted to 14, 28 or 40 shoots per vine (approximately 10 to 26 shoots per meter) following budbreak. Additional adjustments were performed as needed during the growing season to maintain treatment integrity. Each treatment was replicated eight times using seven vine plots. The middle three vine spaces in each plot were used for light, canopy assessment, and vine performance measurements. In the first season of study, cluster number and yield per vine improved with shoot density. Vines thinned to 14 shoots produced approximately 2 tons per acre, while vines with 40 shoots produced about 5 tons per acre. Despite producing lower yields and having the greatest leaf area:fruit weight ratio among the treatments, fruit from vines thinned to 14 shoots had the lowest soluble solids in the experiment. Total leaf area per vine increased with shoot density (7 to 9 m2 for vines thinned to 14 shoots and 40 shoots, respectively), while pruning weight was lowest for vines thinned to 14 shoots. Vines with 14 shoots had lower leaf layer numbers, greater numbers of canopy gaps, and higher percentages of exterior leaves and clusters, compared to vines with 28 and 40 shoots per vine. Light penetration within the canopy declined as shoot number per vine increased. Cluster counts will be collected in spring 1997 to determine treatment effects on return fruitfulness.

Influence of Vine Trellis/Training System on Growth, Yield, Fruit

The experiment being conducted is a long term investigation of the influence of training system on vine performance and the incidence of Eutypa dieback in a Cabernet Sauvignon vineyard. The goal of this experiment is to develop cultural practices which will reduce vine losses from Eutypa and reduce production costs without a reduction in yield or fruit quality. Warm weather produced excellent early season growth which enhanced canopy development and advanced fruit maturity. Minimally pruned vines were skirted in early June to reduce crop load and facilitate cultural practices. Symptoms of Eutypa infection were observed in the plot during Spring 1996 for the first time. Additional vines with foliar symptoms of Eutypa were identified during Spring 1997. Eutypa symptoms were only observed in hand-pruned, cordon-trained treatments. Training system had a significant effect on yield and components of yield in 1996. Yield was higher for the minimal pruning treatment and lowest for head trained – cane pruned treatment. High yield resulted from increased clusters per vine. Cluster number was greatest for minimally-pruned vines while cluster weight, berry weight, and berries per cluster were among the lowest when compared to the other treatments. In general, large yield for the minimal pruning treatment resulted in delayed fruit maturation. Soluble solids and pH were lower for vines which were minimally pruned. Potassium content was greatest for the Hudson River Umbrella treatment and lowest for the machine pruning with hand follow-up treatment. Titratable acidity and anthocyanin content did not differ significantly between treatments. Training system also had a significant effect on vegetative growth. Growth, as measured by mature nodes per vine, was greatest for bilateral cordon and lowest for minimally pruned or machine pruned vines. Vines which were minimally pruned had more shoots per vine than all other treatments.

Modification of Wine Characteristics Through Irrigation Management

We propose to develop an approach to vine water management appropriate to cooler growing regions that will provide growers the tools they need to know when to begin to irrigate, when to schedule subsequent irrigations and how much water to apply each time they irrigate. This research project will utilize measurements of xylem (leaf) water potential (XWP) as a trigger to determine when to begin supplying irrigation water. After a threshold XWP has triggered the start of the irrigation season, water will be supplied at a fraction of the full vine water use. It is our goal to use water management, as defined as the timing and quantity of applied water, to impose vine water deficits as a means of producing desirable must and wine characteristics. Irrigation management strategies for red winegrape varieties have not been developed for mature vines in cool regions. Climate demand and soil moisture loss variables are commonly used to schedule irrigations in the warmer growing regions in the state; however, these can grossly over estimate the amount of water necessary to insure high fruit quality. Growers are aware of this and realize they must “deficit irrigate” their vines in order to maximize fruit quality. This project will give them the tools they need to select an irrigation management strategy that integrates climate variables common to the cooler growing areas such as spring rains and summer fog.

New Parameters to Measure Ripeness

Grape samples were collected at two Oakville area vineyards during an 8 week period for analysis of phenolics. Wines were also made from these two vineyards at three different maturity stages. All samples are being analyzed for phenolic content using a relatively new procedure which separates phenols based on size. This year of the project was designed to replicate last year’s effort in order to test for year to year differences, and to expand the use of a new analytical method which is capable of measuring polyphenols from both skins and seeds. At this point, all the samples have been collected and extracted. The chromatographic analysis of the seeds is complete, but the skin and wine analyses are still underway. Preliminary analysis of sensory data on the wines prepared by Mondavi winery for both bitterness and astringency shows increasing astringency with ripeness, the same as last year’s wines, but also shows a trend for increasing bitterness. While these trends are interesting, further statistical analysis will establish the significance of the sensory data. The goals of this year of the project were to: 1) Repeat the measurement of the levels and polymer distribution of phenolic compounds during ripening in vineyards selected in consultation with NCVRG representatives. 2) Compare maturity with specific chemical levels. 3) Prepare, in consultation with NCVRG representatives, wines from the same vineyards at different stages of maturity. 4) Analyze the wines using the same procedure to see if the changes observed in the grapes follow through to the wine.

Optimal Viticulture Systems Comparison

The dual experimental constraints of only two years of data collection (1995 and 1996) and relatively few differences among patterns of viticultural practices applied to the three types of treatment plots (i.e., organic, biologically-intensive, conventional) suggest the wisdom of extreme caution in attempting to draw biologically meaningful conclusions from results thus far in the study. However, several patterns of numerical trends indicate directions in which experimental results appear to be progressing. Total soil nitrogen analysis demonstrated differences of only 0.006%between 1995 and 1996, along with a nearly identical tight range of data grouped by treatment for 1996 (0.005%), as well as for 1995 and 1996 combined (0.006%). Data for soil microbiology activity indicates that conventional plots had higher biomass levels than organic or biologically intensive plots. Overall, one should be safe in concluding that no substantially significant differences across treatment plots for the soil chemistry and microbiological parameters as measured in this study were revealed through the 1996 sampling period. Nutritional status of the vines was greatly reduced from the adequate levels expressed during 1995. Nitrogen levels were half of their 1995 levels while magnesium, zinc, and manganese levels showed increases over 1995 levels. There was never any significant differences between nutrient levels in any of the treatments. During 1995 and 1996, arthropod data were collected for the herbivorous western grape leafhopper (Erythroneura elegantula), along with a wide array of natural enemies (i.e., predators and parasitoids), at approximately two-week intervals. With WGLH nymph densities throughout both 1995 and 1996 generally averaging well below 5 per leaf, very little differences between treatments could be reliably detected. The slowly developing grapevine canopy yielded very few beneficial arthropods sampled by leaf counts in 1996. A tremendous number of spiders were collected by pitfall trap sampling in this study during.1996: over one-half million (508,017) spiders were recorded! However, of the half-million spiders trapped in 1996, nearly 95% (3265/3456) belonged to the family Lycosidae, commonly known as wolf spiders and virtually never being found in the grapevine canopy itself. Thus, although these highly abundant lycosid spiders are most certainly generalist predators, the prey upon which they were feeding in 1996 most likely was limited to small soil-dwelling arthropods, which may themselves have had little distinct involvement (good or bad) with the grapevine canopy proper.

Water Use and Effects of Deficit Irrigation on Chardonnay Grapevines

A study is being conducted to determine the water use or vineyard evapotranspiration (ET) of Chardonnay grapevines subsequent to vineyard establishment. ET is the combined loss of water by evaporation from the soil and transpiration by the vine. The experimental vineyard is located in the Carneros District of Napa Valley. In addition, the vines are grafted only two different rootstocks (110R and 5C) to determine if there are differences in water use between them. Lastly, five irrigation treatments were imposed to determine the effects of both under and over-irrigation on vine physiology and growth and wine quality. Vine water use is determined by measuring soil water depletion and the addition of water during an irrigation. Soil water content is being measured with a neutron probe at eight sites throughout the vineyard, four sites per rootstock. Vineyard water use in 1996 at full ET (i.e., water applications equal to vine water use) were approximately 470 mm (18.5 inches). Deficit irrigation of vines resulted in the depletion of soil water, the amount dependent upon water application amounts. To date there has been no difference in water use between the two rootstocks. Water applications less than full ET result in more negative leaf water potentials and lower stomatal conductance and photosynthesis. The percent reduction is a function of the amount of water applied. There are highly significant correlations between the grapevine’s water status and soil water content when measured on the same day. There were significant reductions in berry size for vines that were deficit irrigated in 1996. There has been no differences among irrigation treatments with regard to juice pH. Titratable acidity increased with increasing water applications. There were minor differences in berry composition among the rootstocks in 1996; however, there were no significant interactions among rootstocks and irrigation treatments. Experimental wines made in 1996 are currently being analyzed. Preliminary results indicate a preference for wines made from the 50%to full ET irrigation treatments.

Alternatives and Improvements to Soil Fumigation with Methyl Bromide

We have now reached the point where certain treatments are ready for field evaluation in certain field settings. Our research is now taking two directions. First, we need to continue small plot evaluations in our search for additional root killing agents of any kind. Second, we need to conduct field evaluations of combinations of the successful treatments listed above. These include:

  1. Use of Telone and Vapam drench through existing mirco sprinklers or drippers where resistant stocks are to be used or nematodes are not present.
  2. Use of Vapam at 100 to 150 gallons/acre where ectoparasites are the problem.
  3. Use of Urea drench followed by sudan grass where root kill has been accomplished by some other means. We are ready to do this in walnuts.
  4. Use of high rates of Vapam then waiting one year.
  5. Use of Garlon plus diesel painted to cut trunks in late summer after harvest.

Evaluation of Trellis Training Systems and Subsurface

The 1995 season represents the initial year of data collection for this project. Irrigation method had little effect on vine performance or fruit composition in 1995. Above ground and subsurface drip irrigation performed in a similar manner for yield and quality parameters. However, some differences were noted in the management of these irrigation systems. Use of subsurface drip irrigation allowed for reduced application of herbicides. One application of glyphosate to perennial weeds could be avoided because berms were dry. Conversely, use of subsurface drip irrigation required increased efforts for control of gophers. Significant trellis/training system effects were observed in 1995. Yields were highest for divided canopy systems and minimal pruning. Increased yield resulted from higher numbers of clusters per vine. There was an inverse relationship between yield and berry and cluster weight. Fruit maturation was delayed significantly for the trellis/training systems which had the highest yields.