The Regulation of Fruit Growth, Fruit Composition, and Wine Composition by Water Management

This project quantified the role of cluster microclimate in water stress responses, tested the importance of stress at veraison, and extended what we learned about seasonal water stress in hillside Cabernet franc and Sauvignon blanc production in Napa Valley to additional sites and varieties. Soil and vine water status is readily controlled in drip-irrigated vineyards of Pinot noir (Carneros) and Cabernet Sauvignon (Lodi). Changes in vineyard water status, yield, and fruit and wine composition caused by pre- (Early Deficit) and post-(Late Deficit) veraison stress were similar to our earlier results. Thus, those results, showing control of yield and fruit composition, can largely be extrapolated to valley floors and are not indicative only of hillside vineyards with shallow soils and high exposures. The results also show the utility of drip irrigation for control of vine water status and the prevalence of water deficits in winegrape production in the North Coast. Thus, many growers can control vineyard water status and, because of this, color, phenolics, malate, and amino acids, and other compounds in the fruit. Light penetration into the canopy increased in Early Deficit vines early in the season compared to other treatments. After veraison light penetration increased slowly in C vines and rapidly in Late Deficit vines, in part due to differences in the rate of leaf drop. The role of microclimate in the stress responses of fruit development was investigated with reciprocal treatments that, e.g., created in some well-irrigated vines a canopy that mimicked the canopy of Early Deficit vines and vice versa. Temperature in the cluster zone did not differ significantly among any treatments, and, therefore, was unlikely to explain the differences that we observed in fruit and wine composition. However, differences in the light environments were important in establishing part (less than 50%) of the decreased pH and and increased color of Early Deficit wines. This shows that water deficits can be used to improve canopy structure. Water stress at veraison was not found to be critical for controlling fruit composition. However, the timing of the water stress was important in determining sensory attributes because judges could easily discriminate between wines made from Early Deficit and Late Deficit vines.

Spiders in Vineyard Agro-Ecosystems

The overall goal of this research project is to continue to elucidate the ecological roles, along with the potential economic value, of spiders in vineyard agro-ecosystems. Key objectives include determining which spider species may be directly associated with vineyard cover crops, and further delineating the patterns of abundance and distribution of important spider species in vineyards. One clear pattern beginning to emerge is an inverse relationship between spider and leafhopper densities in vineyards. Our findings in this and other studies agree with several other vineyard spider researchers in demonstrating that when spiders are abundant, leafhoppers generally tend to stay below economically damaging levels. The two most abundant spiders sampled from mid-June to the end of November in 1992 belonged to the family Clubionidae (two-clawed hunting spiders): Trachelas pacificus and Chiracanthium inclusum. Juveniles for these two species were roughly three times as abundant as adults in samples taken throughout the season. The next most abundant spider was Theridion (family Theridiidae), which was also of particular interest by being detected only in the grapevine canopy (i.e., almost never from the cover crops between vine rows). It should be noted that the most abundant spiders commonly detected in both cover crops and canopy were Trachelas and the micryphantids. Another particularly noteworthy discovery during the 1992 season involves an apparent correlation between western grapeleaf skeletonizer (WGLS) mortality and Trachelas pacificus occurrence. Corrugated cardboard bands wrapped around the base of vines are very effective in concentrating WGLS larvae seeking pupation sites. Bands which individually contained up to 70 WGLS pupae typically were found to be free of spiders. However, it was also not uncommon to find bands with only 5 to 10 WGLS pupae; in virtualy all these cases a large number of Trachelas juveniles were also found residing in those bands. Additional data collected in “round-the-clock” sampling trials during 1992 indicated that in estimating population densities for several important spider species, the actual time of day when samples are taken can be of considerable importance.

Influence of Windbreaks on the Vegetative and Reproductive Growth

Spring and summer months in the Salinas Valley are characterized by strong daily winds. It is widely held that vine growth and productivity in this region are reduced due to the presence of excessive wind. Chardonnay, the major wine grape cultivar of this region, appears to be particularly sensitive to excessive winds. Salinas Valley wine grape growers have recently expressed interest in the use of windbreaks to increase vegetative and reproductive growth. The long-term effects of windbreaks on vine vegetative growth, yield components, fruit composition, and wine quality have not been adequately investigated. A study was initiated in spring of 1991 to determine the effects of windbreaks on the vegetative and reproductive growth of Chardonnay grapevines in the Salinas Valley. Grapevines grown in artificial wind shelters were compared to grapevines exposed to ambient wind (control). Wind speed was reduced by up to 50%within the shelters, depending upon sensor distance above ground. Marked differences in the vegetative and reproductive growth of sheltered and non-sheltered vines were observed in both seasons. Sheltered vines had significantly larger primary and lateral leaves, and greater primary and total leaf areas compared to the control vines. The specific weight (mg dry weight-cm’2 leaf area) of both primary and lateral leaves was greater for the control than for sheltered vines. The number of nodes per shoot was similar for both treatments, however, the internode length of sheltered vines was significantly greater than the internode length of non-sheltered vines. The rate of shoot growth was also significantly greater for sheltered vines than for non-sheltered vines. Stomatal conductance and carbon assimilation rate were slightly greater for sheltered vines than for unsheltered vines, while no difference was found in leaf water potential between the treatments. Significant differences in vine yield components were not observed between the treatments in 1991. However, in 1992 cluster number, cluster weight, and fruit yield of sheltered vines was greater than for non-sheltered vines. Fruit and must composition were similar for both treatments. The results indicate that sheltered vines produced higher yields than non-sheltered vines due to their greater vegetative growth and vine capacity. Sensory evaluations of wines produced in 1991 and 1992 will be performed in the upcoming season.

Influence of Potassium Deficiency and Temporary

Executive Summary The aim of the proposed research was to study several sites with a history of potassium deficiency using a rapid screening procedure for putrescine levels that we developed in previous work on this project. The objective was to validate our screening procedure and provide recommendations regarding sampling time so that putrescine screening can be used routinely for managing potassium deficient vineyards. During the 1992 season we analyzed leaf samples for putrescine by HPLC and a recently developed TLC screening procedure that increased sample throughput by an order of magnitude. Results show that our screening procedure can certainly be used for Cabernet sauvignon and Chardonnay and can probably be used with other varieties. The screening procedure can be used to detect elevated putrescine in leaves at bloom whether or not leaf symptoms are present. The screening procedure is equally useful at veraison and after harvest. In all cases when samples were scored by TLC as having increased putrescine, the result was confirmed by HPLC. False positives and false negatives were not observed. Putrescine in leaves as estimated by the screening procedure correlated well with a subjective evaluation of the degree of potassium deficiency suffered by the vine. Results obtained during the 92/93 season served to validate of our screening procedure. We can now provide specific recommendations regarding sampling time so that putrescine screening can be effectively used for managing potassium deficient sites. In addition we have identified several “ideal” locations to apply the procedures we have developed. Interestingly, we found one site in our study that did not fit the typical potassium deficiency syndrome. This site provides an opportunity to characterize other disorders besides potassium deficiency that can lead to increased putrescine levels in the leaves.

Evaluation of Winegrape Clones

Thirteen clones or selections of Pinot noir were harvested for sparkling wine. Large differences were seen in maturity. Plots picked at 19 Brix were harvested over a 3-week period from August 21 through September 10. Yield was correlated more with cluster wt and cluster number than with berries/cluster. Among the clones, large differences were seen in virtually all measured parameters, including pruning wt, the several yield components, and in juice yield/ton of fruit. Duplicate wine lots were made from each clone or selection. Three clonal wines were rejected (both lots): one clone was defective in its aroma and two clones were lost because they underwent malo-lactic fermentation. The remaining 10 clones or selections are undergoing duo-trio analysis and further evaluation by cooperating winemakers. Further analysis of previous years’ data from two Chardonnay plots and one Cabernet Sauvignon plot reveals a close correlation of yield with cluster wt, more so than cluster number. For both varieties, there was a slight negative trend of pruning wt with yield, indicating that some yield increases were obtained at the expense of growth or that the yield:prunings ratio could have been altered by formula pruning, i.e. adjusting the buds retained at pruning based on the pruning wt. The Zinfandel clonal trial suffered heat damage and fruit shriveling prior to harvest skewing the data and resulting few reliable differences. Other trials with Merlot, Cabernet Sauvignon and Chardonnay are maturing and will be available in the near future.

Clonal Testing of Winegrapes in the San Joaquin Valley

An on-going San Joaquin Valley wine cultivar clonal evaluation trial was initiated in 1986 and planted into the first trial block in 1987. Location is the University of California Kearney Agricultural Center, Parlier where cultural conditions and practices can be closely monitored. All of the selections are indexed FPMS sources, most of which are registered. None have ever been compared in clonal studies in California. Thus, industry would benefit from performance information on available selections. This study utilizes 15 single-vine replicates in randomized complete blocks for each cultivar. 1992 was the fourth year of comparison for three selections each of French Colombard and Chenin blanc. Each cultivar compares two different selections which are registered (indexed as virus free) but not heat treated. Additionally, each cultivar includes a heat treated selection. Thus, we are studying the possible influence of heat treatment on virus-free material of French Colombard and Chenin blanc. Barbera was in its second year of data taking. This compares an Italian selection, Rauscedo 6 (FPMS Clone 2), with Marshall (FPMS Clone 1). Barbera Clone 1 presently involves much of the present commercial acreage but was later found to contain mild leafroll. French Colombard. Clone 5 was the only selection to show significant differences in 1992, with higher yields due to heavier clusters. The heavier clusters were due to more berries per cluster. This higher yield also contributed to lower fruit soluble solids of about l°Brix as compared to Clones 1 and 2. These results were different from those of past years when Clone 1 and Clone 5 were highest and lowest in yield, respectively. Clone 2 was the best overall selection in previous years but showed no benefits in its performance in 1992. Therefore, two more years of data taking are anticipated in order to better determine long-term differences. Chenin blanc. Clone 5 again produced the smallest berries and clusters of earliest maturity. However, rot also continues to be highest with this selection. Clone 4 continues to appear to be the best selection as it has had the highest yield and lowest rot incidence in the past. It was also more fruitful than Clone 1 in 1992. Clone 4 is a heat treatment of Clone 1. This is an interesting comparison, as the heat treated selection (Clone 4) has more favorable vine yield characteristics than Clone 1. 10-1 Barbera. These two selections were included to compare the widely planted Clone 1 (Marshall) with the only registered and recently introduced Clone 2 (Rauscedo). Because of its virus-free status, Clone 2 would appear to be the recommended choice for future planting. However, its larger berry size and higher yields contribute to later fruit maturity and lower fruit anthocyanin content. Thus, harvests in future years will be made at the same stage of fruit maturation rather than calendar date. This will enable us to more accurately compare fruit composition effects on wine quality. Wines were made from all of the selections in 1992. These results will be reported at a later date when sensory analyses have been completed. Zinfandel was eliminated in 1991 due to inclusion of a misnamed selection. Grenache, Sanqiovese, and Muscat blanc trials were established in 1993 with 3 selections of each cultivar.

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

Large scale replicated trials were initiated in the fall of 1991 on three farms in the San Joaquin Valley. The first year’s data was collected during the 1992 season. In general, we observed an increase in the activity of natural enemies, especially spiders which resulted in a suppression of leafhopper numbers in some vineyards. The numbers of leafhoppers during the 1992 season were too low to observe a strong effect of cover crops on their numbers. Whole-vine spider exclusion and spider caging with leafhoppers indicated that the most common spiders in vineyards are important predators of leafhoppers. Continued monitoring of our vineyards is necessary to determine the long term effect of cover crops on the numbers of pests and their biological control agents. Our results on weed suppression with dry mulch is variable. However, our studies and those conducted by C. Elmore in north coast vineyards indicate that yearly accumulation of biomass in vine rows should provide sufficient weed suppression to minimize the use of herbicides. In table and wine grape vineyards, cover crops left to dry in row middles can suppress weeds, conserve soil moisture, decrease mowing costs, and reduce dust problems. The data on the nutritional status of vines did not show any treatment differences. This is not surprising, however, since the effect of cover crops on mineral nutrition of vines is a delayed effect, often not detectable until the following year. Our initial budget for alternative floor management systems indicates that the use of cover crops for weed management may increase the cost of grape production, primarily due to the added cost of cover crop seeds. This increased cost, however, should turn into savings when insecticide and fertilizer costs are included in the enterprise budget. It is anticipated that our cover crop system will reduce insecticide, herbicide, and fertilizer inputs. In the long term, seed costs should also be reduced, since the cover crops used in our studies are self-seeding.

Impact of Fungicide Use on Wine Quality

The purpose of this continuing research project was to investigate the use of combinations of sulfur and commercial fungicides to determine, if control of powdery mildew could be achieved with minimum or no sulfur residues remaining on the grapes themselves or in wine produced from those grapes. The judging panel could distinguish all of the white wine lots and two of the red wine lots from the control indicating some “sulfur” problems. These results indicate that late season applications of sulfur dust, in conjunction with the use of a fermenting yeast known to produce larger amounts of hydrogen sulfide, have the potential to produce off aromas in both red and white wines.

Improving nitrogen fertilizer efficiency in winegrapes

This was a four-year study on the effects of N fertilizer timing and rate on vine N status, fruit composition and quality, and vine yield in four wine cultivars important to the San Joaquin Valley — Barbera, Grenache, French Colombard, and Chenin blanc. It was initiated as a follow-up to previous studies in raisin and table grape vineyards which demonstrated the influence of N fertilizer timing on N availability and utilization and possible improvements in N fertilizer efficiency. Similar studies are needed in wine grape vineyards to determine N timing response as well as effects on vine tissue N levels, fruit composition, and vine yields. N fertilizer treatments included budbreak (BB), berryset (BS), veraison (V), and postharvest (PH) timings at 50 lb. N /ac, BS at 100 lb. N/ac, and check, no N (CKO). N status, as determined by bloom and veraison petiole N03-N and NH4-N (inorganic N compounds) levels, varied among the cultivars and was influenced by rate (0, 50, and 100 lbs. N) and the proximity of fertilizer application prior to petiole sampling date. Grenache and Barbera were the high and low extremes, respectively, in vine N status and responsiveness to N fertilizer application; Chenin blanc and French Colombard were intermediate. Generally, CKO and BS100 were the high and low vine N status treatments through the experiment. PH50 resulted in bloom N levels equal to BB100 and sometimes higher than BB50, suggesting that postharvest timing was the most efficient in supplying N between budbreak and bloom. Otherwise, timing effects on vine N status were minor. Petiole N03-N was more sensitive than NH4-N to N fertilizer treatment differences. However, the sum of the two analyses (expressed as “total inorganic N”) provided the most clear separation among treatment differences and thus could be considered as a useful tool in grapevine N fertility research. Grape soluble solids was the most responsive fruit parameter to N treatment. Generally, N fertilizer tended to decrease soluble solids, irrespective of timing, and with the highest N rate of 100 lbs. resulting in the largest decrease. Titratable acidity differences were mostly inverse to soluble solids. Grenache was the only cultivar with significant yield differences due to N fertilization, suggesting a N-deficient status with this cultivar. All of the N treatments in Grenache, with the exception of V50, increased vine yield over CKO. This result, as well as other negative effects of the V50 treatment, ie.lower titratable acidity and higher pH in Grenache and more cluster rot in French Colombard and Chenin blanc, indicate that veraison may be the least desirable of the timings studied here. The detrimental effects of the high 100 lb.N treatment were also demonstrated, primarily through delayed fruit maturation and some increased cluster rot incidence. The bloom petiole N03-N levels reported here should provide supportive data toward establishing critical vine tissue levels in the wine cultivars studied here.

New technology for determining vine water status and controlling vineyard

We confirmed that ultrasonic acoustic emissions occur in field-grown grapevines subjected to water deficits. The appropriate sensor and frequency for adequate detection was determined. Although we can record acoustic emission rates in the field, we are not satisfied with the present sensor attachment. For Cabernet Sauvignon vines in the Lodi area, differences in the rate of acoustic emissions at the onset of veraison were easily resolved between vines receiving irrigation every other day and vines from which water was withheld up to that point. The rate of acoustic emissions from the stressed vines was two to five times greater than from the irrigated vines at midday. When water was withheld (at 50%veraison) from some vines for only six days, there were again large differences (up to five-fold) in the rate of acoustic emissions at midday. The results suggest that the water status of a vineyard may be estimated daily and automatically without grower labor input.