New Parameters to Measure Ripeness

The goals of the first year of this project were to: 1) Analyze the changes in the phenolic “profile” of extracts of grapes from unripe to ripe to overripe. Focus special attention on the levels of polymeric phenolics. 2) Determine the chemical structure of the constituents that change over this time period. 3) Prepare wines from each grape sample and compare their sensory characteristics. 4) Determine if the changes observed in the grapes parallel the wine’s content. During the 1994 vintage, two Mondavi vineyards were tised to provide samples for analysis and winemaking. Grape berries were separated into skins and seeds, the two tissues were extracted, and each extract analyzed for monomcnc (and some dimeric) phenolic compounds. By spectral analysis of all peaks, more than 90%of all the components were categorized into classes of phenolics and the amounts of each class totaled. In addition, wines prepared at different stages were analyzed in a similar manner, as well as the pomace from the fermentation. The goals outlined above has essentially been completed except tor the analysis of the polymeric constituents. However, our data was not as precise as desired due to sample variability. Consequently, it is difficult to observe any trends other than the decrease in catechin levels during ripening. This change in catecliin levels does suggest that there may be a change in the polymer distribution of flavan-3-oLs. We will address this issue by analyzing wine samples with a chromatography system that separates these compounds based on their molecular weight.

Influence of Vine Trellis Training Systems on Growth, Yield, Fruit Composition, and Eutypa Incidence of Cabernet Sauvignon Grapevines

This is the third season of a long term study to investigate the influence of trellis / 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 loss in fruit quality. Vines had good early season growth with the exception of vines which were head-trained and cane-pruned. These vines displayed poor development of buds in the middle of canes. Minimally-pruned vines grew well and appeared to develop a full canopy by May. We observed that early season leafhopper damage appeared to more severe on minimally pruned vines due to their early completion of shoot growth. Minimally-pruned vines were skirted (trimmed) at approximately 36″ above the ground to reduce crop and facilitate cultural practices during June. Also, an additional drip emitter (0.5 gallon) was installed for each minimally-pruned vine to compensate for the higher water requirements of this treatment, especially early in the season. Significant differences in yield and fruit composition parameters were observed in 1994. Minimal pruning and machine pruning treatments had significantly higher yield and number of clusters than the other treatments. The head trained/cane pruned treatment had significantly lower yield than the other treatments. Treatments .with the higher yield i.e. minimal and machine pruning displayed a slight delay in fruit maturation. Trellis / training system did not significantly affect total growth of vines as indicated by mature nodes per vine. Nodes retained were highest for the minimal and machine pruning treatments. Symptoms of Eutypa lata infection have not been observed in the experimental block.

Influence of Trellis-Training System and Rootstock on Optimum Spacing of Cabernet Sauvignon Vines Within Rows

The second year’s data from five-year-old Cabernet Sauvignon vines grown at the south Oakville Experimental Vineyard comparing within row vine spacings of 1, 2, and 3 meters showed average crop yields of 8.8, 8.3, and 7.3 tons/acre, respectively, when data of six trellis systems and two rootstocks were averaged together. The higher yield of closer vine spacing was mainly due to greater number of vines, shoots and clusters per acre, and to a lesser extent, berry weight. The number of berries set per cluster and cluster weight decreased with closer vine spacing but this reduction was more than made up for by the increase in shoots and clusters per unit area of land from higher planting density. The differences in yield between in-row spacing treatments was only 20%in 1994 compared to 63%in 1993, suggesting that dif¬ferences in yield due to within row vine spacing may disappear as the vines become older. With wider vine spacing there was an increase in the number of shoots, leaf area and pruning weight per vine but reduction of these parameters per meter of row length. Shoot length, leaves/shoot, internode length, leaf area per shoot and leaf area per gram of fruit decreased with increasing distance between vines within rows. The overall effect of increasing distance between vines was a reduction in canopy density and an increase in the amount of photosynthetic light in the fruiting region. The total leaf area (m2)/m row length was reduced from 4.6 for 1 m vine spacing to 2.8 for 3 m spaced vines when averaged for all trellis systems and both rootstocks. Pruning weights were similarly reduced on a per meter of row basis from 1.5 for 1 m spaced vines to 0.8 kg/m for 3 m spaced vines. Increasing the distance between vines from 1 m to 3 m sig¬nificantly reduced the level of TSS, pH, malic acid and anthocyanin per berry in fruits at harvest, however TA, K, and anthocyanin per g berry weight did not differ significantly between vine spacing treatments. Increasing vine space also reduced wine pH (and for the GDC, wine TA) but did not significantly effect ethanol concentration, wine color density or wine hue. The yield of Cabernet Sauvignon or 110R rootstock averaged 9.0 tons/ac compared to 7.1 tons/ac for 039-16 stock. The higher yields obtained with 110 are compared to 039-16 stock was true for all vine spacing and trellising treatments. The higher yields produced with 110R stock was mainly due to greater number of shoots and clusters per vine and to a lesser extent to larger berries. Shoot length and leaf area per shoot of vines on 110R stock were about 30%greater than vines on 039-16 stock. Total leaf area per vine aver¬aged approximately 50%higher with 110R than 039-16 stock. Total pruning weight per vine and average shoot weight were almost doubled on 110R relative to 039-16. The greater density of 11 OR resulted in a reduction in the amount of light in the fruiting region, however, the level of light did not limit fruit bud formation and vine productivity. The ratio of leaf area/g fruit averaged 8.4 for 039-16 and 10.1 for 110R. Crop to pruning weight ratios were 9.1 for 039-16 and 6.2 for 110R. 110R fruit at harvest was significant¬ly higher in TSS, pH, K and anthocyanin than 039-16 fruit. Wines from Cabernet Sauvignon on 110R

Improvements and Replacements for Pre-Plant Soil Fumigation

Garlon at 5 and 10 grams active ingredient applied to foliage or applied as a paint to stumps was highly effective at killing the surface 1 foot of grape roots and all aboveground portions. It was ineffective, however, at killing roots below 1 foot soil depth. Certain grape rootstocks are more sensitive to the replant problem than others. Teleki 5C is among the more sensitive, whereas own-rooted V. vinifera appears less sensitive. We now have good evidence that Vapam at 100 gpa is a mediocre performer relative to killing old roots and that treatments with Vapam, like methyl bromide or Telone, result in a biological vacuum. By broadcast drenching at 200 gpa and then growing nonhosts for the nematodes in the next year we have in one large trial achieved nematode control and vine growth comparable to that achieved with methyl bromide. We now need to adjust the treatment rates lower to find the best rates for use in vineyards as compared to orchards. Telone or Acrolein applied via a drencher at rates equivalent to 100 gal/acre Vapam will outperform Vapam. Applied via drencher Telone volatilization can be reduced from that which occurs after conventional shank injections.

Identifying the Potential to Use Vineyard Water Status to Alter Anthocyanins and Other Phenolic Compounds in Red Winegrapes

The data from field experiments with Cabernet Sauvignon grown near Lodi show that clear differences in vine water status were obtained at different stages of development by withholding water. Although water status of vines irrigated every 2-3 days (Continual treatment) decreased until veraison, when water was withheld from the beginning of the season (Early Deficit) or from times closer to veraison (Veraison Stress and Moderate Veraison Stress) vine water status decreased significantly more rapidly resulting in differences in vine water status of about 3 bars at veraison. When water was withheld after veraison (Late Deficit), vine water status rapidly decreased to values that were about 4 bars more stressed than the Continual vines. This was sufficient stress to cause some leaf senescence and abscission. The general response to water deficits was for phenol ics and anthocyanins to increase in concentration although this is not uniformly the case. For anthocyanins, the accumulation that occurs at veraison was induced earlier in vines that were water stressed. The minor anthocyanins were more responsive to early stress, whereas the major anthocyanin compound, malvidin-3-glucoside, accumulated to the highest concentration in Late Deficit fruit. The responses of juice phenolics in general and cinnamates specifically to water stress were complex and depended on the specific compound. Some accumulated during ripening and some decreased in concentration after veraison. In general, most juice cinnamates were present at harvest in highest concentrations in Late Deficit fruit. Nonanthocyanin skin phenolics were predominately flavanoids which accumulated during ripening. The accumulation was more rapid and to higher concentrations in vines that were exposed to early stress (Early Deficit and Veraison Stress) and lowest in vines that were exposed to high water status early in fruit development. Analysis is continuing of the specific nonanthocyanin skin phenolics. A new field trial has been established in a premium Cabernet Sauvignon vineyard (Knight’s Valley). In this trial similar data will be developed but more samples will be collected late in fruit ripening for determination of the relationship of the concentration of specific compounds with Brix, TA, and “hang time” and their responses to early and late season water deficits.

Evaluation of Microsprayers for Frost Protection in California Vineyards

The experimental site was a Chardonnay vineyard located near Los Alamos, CA. Plots were established during early March 1993 and data were collected from March 11, 1993 through May 20, 1993 and March 14, 1994 through May 23, 1994. The microsprayer (Wade Pulsator?) under evaluation uses a pulsing action that produces larger diameter droplet sizes, while maintaining lower application rates as compared to those found with conventional microsprayer design. This microsprayer produces a narrow band of water (approximately 24 inches wide) directed over the cordon of the vine. Microsprayers were installed in every vine row and mounted 22 inches above the cordon on every other stake, approximately 10.5 feet apart. A five acre block of microsprayers was compared to an adjacent sprinkler block. The sprinkler block had a typical design and installation for commercial coastal vineyards. Sprinkler spacing was 50.0 feet X 42.0 feet, using a conventional impact type head and a 7/64 inch nozzle. The water source for both systems was an above ground reservoir filled by pumping ground water. Water was passed through a perforated tube filter for the sprinklers and a sand-media filter for the microsprayer system. Water use was measured by a Rockwell sealed register meter. Data collected for the microsprayer and sprinkler blocks were bud temperature, air temperature, and relative humidity. Air temperature was also recorded at 18 inches from the cordon and the middle of the vine row (at cordon height). Environmental conditions monitored outside the vineyard were air temperature, wind speed and direction, and relative humidity. Environmental data were collected with Omnidata data loggers using a series of thermocouples for bud temperatures (attached at bud locations) and Physchem RH sensors’for air temperature and relative humidity. A data logger and associated sensors were located within the microsprayer and sprinkler blocks and outside the vineyard. Due to the low number of spring freezing events in 1993 and 1994, data collection was limited at the vineyard site. During the spring freezing events which were monitored, microsprayers provided a level of frost protection which was similar to that provided by sprinklers. Also, the use of microsprayers resulted in a savings in water use of approximately 80 percent during selected freezing events. This was a preliminary experiment and further research is needed before general recommendations can be given. Continuing studies will include a series of tests under controlled freezing conditions in a cold chamber.

Clonal Testing of Wine grapes in the San Joaquin Valley

The San Joaquin Valley wine cultivar clonal evaluation study was initiated in 1987. It is an ongoing study to evaluate the most promising, virus disease-free clonal material being held or introduced as potential FPMS source material. 1994 was the sixth and last year of evaluating three selections each of French Colombard and Chenin blanc. Each cultivar comparison involves two different selections which are registered (indexed as virus free) but not heat treated. Additionally, each cultivar includes a heat treated selection. Thus, we have been studying the possible influence of heat treatment on virus-free material of French Colombard and Chenin blanc. Barbera was in its fourth year of data taking. This compares an Italian selection, Rauscedo 6 (FPMS Clone 2), with Marshall (FPMS Clone 1). The Marshall clone presently involves much of the present commercial acreage but was found to contain mild leafroll after many plantings were completed. French Colombard. Overall, all three clones were fairly similar in response for consideration in commercial plantings. However, Clone 2 could be considered to be the most favorable selection due to minimal bunch rot problems and consistency in yield and fruit characteristics over the years of study. Differences due to heat treatment were found when comparing Clone 1 (no HT) and Clone 2 (91 day HT). Clone 2 had heavier berries, fewer berries per cluster, and a trend towards lower bunch rot incidence as compared to Clone 1. There were no significant differences in wines made from the clones in 1993. All three clones are being maintained by FPMS with Clone 2 “Registered” for qualification as California Foundation Stock. Chenin blanc. Clonal and heat treatment differences were greatest with Chenin blanc. Heat treatment resulted in higher cluster numbers and yield with Clone 4 and without corresponding negative effects on fruit composition. For this reason, Clone 4 is recommended above non-heat-treated Clone 1. Clone 5 was a big disappointment. Its higher cluster numbers with smaller berries and clusters were thought to be potential characteristics for lower bunch rot and higher wine quality. However, the clusters were very compact and showed almost twice the bunch rot potential as the other clones. Also, sensory analysis comparisons of the wines in 1993 showed no significant differences. Currently, recommended Clone 4 is “Registered” for qualification as California Foundation Stock. Barbera. Clone 2 (Rauscedo 6) would appear to be the recommended choice for future planting, given its virus-free status and higher yields as compared to Clone 1 (Marshall). However, there has been some delay in fruit maturation, a higher potential for rot, and lower wine color with Rauscedo in past years. Differences were relatively minor in 1994, with no yield differences between the clones and with Rauscedo only having heavier berries and clusters as compared to Clone 1. One more year of field data and wine quality comparison will enable us to make a more definitive recommendation. The problems with Rauscedo point to the need to clean-up Marshall with shoot tip culture as well as the importation of additional Barbera clonal material. Grenache. Sangiovese. Muscat blanc. and Muscat of Alexandria. Trials with 3 clones each were established in 1993 and will begin fruiting for data collection in 1995.

A Cover Crop System for Vineyard Pest, Weed and Nutrition Management

This report describes a continuing on-farm project evaluating the use of two cover crop-based systems for pest, weed, and vine nutrition management in California vineyards. In two large vineyards, from 1992 to 1994, we compared two systems that used a winter annual, oat/vetch cover crop to a system that used clean-cultivation and conventional methods of chemical soil amendments and weed control. In one cover crop system, we used the cover as dry mulch by cutting the cover biomass and placing it on row berms for the suppression of annual weeds without the use of soil-applied herbicides. In the other cover crop system, the cover was cut and left in row middles, but as in the clean-cultivated system, weeds on berms were controlled chemically. Another vineyard was used during the 1992 season to determine the relative impact of spiders and other abiotic factors on leafhopper biology and abundance. We also initiated two additional experiments in 1993 using a merced rye/vetch cover crop, to compare a cover/mulch system with clean cultivation in a 2-acre vineyard located at the Kearney Agricultural Center. A large commercial vineyard located near Madera was used to compare clean cultivation to cover crops used as green manure or as reseed. We determined the impact of these systems on vine-nutrient status, weed suppression, and leafhopper pest and their natural enemies. We also developed operating cost budgets for each management system. The effect of cover crops on leafhoppers and their natural enemies varied between years and vineyards. Our findings to date indicate that, if properly managed, winter annual, legume/grass cover crops can reduce the use of insecticides for leafhopper control. Where leafhopper numbers were not very low and cover crops were properly maintained through early July, the presence of cover crops resulted in reduced infestations of leafhoppers. These reductions may be attributed in part to enhanced activity of certain groups of spiders, which were consistently found at higher densities in the presence of cover crops compared to the clean-cultivated systems. Trace-element marking of cover crops indicated that cover crops may also influence leafhopper populations by serving as non-host vegetation which interferes with their movement patterns and perhaps other aspects of their life history. Although cover crops may affect vine physiology (e.g., through changes in soil fertility, soil-water status, etc.) which may in turn affect leafhopper biology, the changes we have observed in vine conditions to date were not sufficient to explain the differences in leafhopper abundance between the cover crop and clean-cultivated treatments. Cage data indicated that leafhopper reproduction and survivorship were not affected by cover crop treatment The effect of cover crops on vine-nutrient status varied between years and vineyards. Cover crops produced positive effects on vine-nutrient status by the second or third year if the cover crops were managed well, but produced negative effects if the cover or vineyard was poorly managed. The positive effects were usually delayed, and were best illustrated by the results from our Fowler site where by the third year, N levels (nitrate-N in petioles) in unfertilized cover-cropped vines were similar to N levels in fertilized clean-cultivated vines, independent of the type of weed management in row berms. Potassium levels were also enhanced by cover crops by the third year at the Fowler site. We have not observed these effects in the Earlimart vineyard where the cover crop was not incorporated until Fall, while weeds were allowed to grow in row middles during the Summer. Under this ground cover management, apparently much of the nutrient content of the cover is either lost by volatilization, or used to grow the resident vegetation during the Summer. At the Kearney and Madera sites (second year), although we have not detected significant changes in vine-nutrient status in the cover crop treatments compared to clean-cultivated treatments, we have observed trends toward higher levels of nitrogen and potassium in vines associated with cover crops compared to clean-cultivated vines. 21 The amount of dry biomass produced by cover crops for weed suppression varied between vineyards. During late winter and early spring, the mulched berms received 1800 to 8,726 lbs of dry biomass per acre, with a total nitrogen content of 33 to 109 lbs per acre. To date, the results from the north coast (by C. Elmore et. al.) and from the San Joaquin valley indicate that with sufficient levels of biomass production, berm mulching should reduce the use of pre-emergence herbicides. The mulch, however, will not control all weeds equally. Perennial weeds such as field bindweed were not controlled, and we do not have enough data on yellow nutsedge to determine if mulching will be effective. We expect that in the long term, yearly accumulation of the dry mulch should incrementally increase the level of weed control resulting in substantial reductions in the use of soil-applied herbicides. ;The effects of cover crops on grape yield and operating costs depended on grape culture, and represented in a trade-off in water, fertilizer, pesticide and resource use. Although significant differences in yields have not been realized in the Earlimart (third year) and Madera (second year) vineyards, berry size and raisin yields were increased significantly higher by the second year at the Kearney site where cover crop biomass was used as dry mulch for weed suppression in row berms. Berry weight was also significantly greater by the third year in cover crop compared to clean-cultivated treatments at the Fowler site. Greater berry weights should have translated into greater raisin weights, but this effect could not be measured as the raisins at the Fowler site were badly damaged by early fall rain.. The partial cost budget indicated that the use of cover crops (despite greater water demand) may significantly reduce operating costs if savings were realized by reducing chemical inputs for insects and mites. These savings are expected to increase if cultural methods (e.g., raised beds with adjacent furrows for irrigation are used instead of flood irrigation) are modified to maintain satisfactory cover crop growth while reducing water use. Despite the encouraging results from the transition phase, several critical questions remain to be addressed in order to assess the long term impact of cover crops on several elements of grape production. At present we do not know what impact our cover crop systems will ultimately have on several elements of soil fertility and water use in vineyards. For example, we do not know if the increased yield at the Kearney and Fowler sites were due to the greater amount of water used to grow the cover crop. In this case, water usage should be controlled as an experimental variable so we can understand why higher yields were obtained in the presence of cover crops. Studies of more than three-year duration are needed to adequately determine the complex relationships between cover crops, arthropod pests, and weeds, and to evaluate their impact on soil fertility, vine nutrition, and vineyard water use. Our hypothesis is that benefits of cover crops to grapevines will increase incrementally through time, and can be measured. We are continuing our research in the Fowler, Kearney, and Madera sites, and we also initiated similar studies in Napa. We are expanding our multidisciplinary expertise to include a soil scientist (Dr. R. Miller) and a grape physiologist (Dr. L. Williams).

Wine Grape Canopy Management Practices in the San Joaquin Valley

This work is a continuation of studies conducted in the San Joaquin Valley toward determining the most effective canopy management practices for fruit composition, quality, and yield while being cost-efficient and adaptable to mechanization. Previous work was conducted on training system and trellis designs and the effects of fruit exposure on yield and fruit composition. The current study compares pruning systems which can be mechanized and are much different in crop level, vegetative development, and canopy configuration. Six systems involving bilateral and quadrilateral cordon training and hand, machine-hedge, and minimal pruning are being compared with French Colombard and Barbera. 1993 was the first year of a 3-year study. The treatments include: bilateral (Bilat.) and quadrilateral (Quad.) cordon training under both hand (Hand) and machine (Mach.) pruning; and minimal pruning (MPCT) is also being compared with and without hedging to adjust crop load after fruit set. Generally, the treatments with the lowest pruning severity (MPCT, followed by MPCT-Adjust, Quad Mach, Bilat. Mach, Quad. Hand, and Bilat. Hand) produced the most clusters of least weight. Thus, the vines tended to adjust crop loads with smaller clusters and berries. This resulted in comparable yields from all treatments except for lower fruit weights from Bilat. Hand and MPCT Adj. in French Colombard and Bilat. Hand and Quad Hand in Barbera. Fruit composition was not affected in French Colombard except for a 2-week delay in harvest from MPCT. Thus, the Bilat. Hand treatment was restrictive in overall yield potential while there was no advantage in MPCT over machine pruning or adjusting crop in MPCT. Overall, this first year of data taking indicates comparable and most favorable fruiting responses among Bilat. Mach, Quad Hand, and Quad Mach with French Colombard. Bilat. Hand and MPCT Adj were lowest in yield and both MPCT treatments showed a 2-week delayed fruit maturation. Fruit composition was affected greatly in Barbera, especially by pruning method, with the hand pruning treatments ripening earliest followed by the machine pruning and then MPCT, much later. Overall, the two machine pruning treatments — Bilat. Mach and Quad Mach — produced the highest yields with favorable fruit composition. MPCT pruning showed no improved yields over machine pruning and ripened much later. MPCT Adj did show some crop adjustment after post-fruit set hedging with heavier clusters and a 1-week earlier fruit maturity as compared to MPCT. The Quad system out-performed the Bilat. system in yields with Hand pruning. However, Hand pruning increased bunch rot in Barbera over the mechanized systems, especially with Bilat. training. For both cultivars, machine pruning with either bilateral or quadrilateral (2′ cordon separation) might be considered the most favorable system overall in this first year. For hand pruning, the quadrilateral system is best. Additional work is needed to determine long-term effects, especially if MPCT may improve over time.

Water Requirements During and After Vineyard Establishment for Chardonnay Grapevines Grown in the Carneros District

ABSTRACT: A study is being conducted to determine the water use of Chardonnay grapevines grown in the Carneros District of Napa Valley during vineyard establishment. Vineyard water use was determined by measuring soil water content with a hydroprobe and measuring applied water and effective rainfall. The arrangement of access tubes at each site allowed us to quantify the amount of water within the soil profile. A decrease in soil water content would indicate that irrigation was not meeting the water requirements of the vines while an increase in soil water content would indicate that irrigation was greater than vineyard evapotranspiration (ET). The soil water content decreased from budbreak until the middle of September and remained constant after that. This would indicate that applied water was less than vineyard ET. Soil water supplied approximately 38%of the 316 mm (12.4 inches) of water used by the vines in that vineyard. Effective rainfall supplied 36%of the water used by the vines. The depth of water extraction from the soil profile extended to greater than 2.0 m (approximately 7 ft). Midday values of leaf water potential measured throughout the season were no more negative than -1.0 MPa (-10 bars) except when maximum, ambient temperatures were greater than 27°C (81°F) . The crop coefficient ranged from 0.2 to approximately 0.7, depending upon the time of year.