Vineyard Management Strategies for Potassium Nutrition and Optimum Winegrape Quality

There has been some clear progress on the potassium (K) fertility issue in symptomatic North Coast vineyards. These vineyards are typically on soils with K fixing clays (some also with high Mg), and often have “not responded” to earlier conventional applications of potassium sulfate. We have used high rates of potassium sulfate (81bs or greater of potassium sulfate per vine) and supplemental irrigation (2 to 4 times the standard rate) to decrease K fixation and increase the availability of K for root uptake. This has successfully increased vine K status and maintained high K status beyond veraison. The genetic approach to managing these soils also looks promising. For Chardonnay vines on low K soil, vine K status was significantly greater on 5C and St. George rootstocks than on four other root systems. Applications of K to these vines increased juice pH on some rootstocks and decreased the concentration of malate on all rootstocks.

The Effect of Application and Timing of Cryolite on Fluoride Levels in Red and White Wines

The main purpose of this experiment was to determine the level of fluoride in red and white wines from grapes sprayed with Cryolite at specific rates and application times. A four-year study at CSU Fresno has conclusively shown that Cryolite increases fluoride levels in red and white wines. From 1990 to 1993, many different rates and timing combinations were tried in order to clarify the role of Cryolite in wine fluoride. In 1993, a 6-pound full bloom rate was the basis for an application and timing trial tested on seven different vineyards in the San Joaquin Valley. The objective here was to determine the minimum Cryolite that would be efficacious and yet produce the lowest fluoride levels in wines. The experiment was conducted at 7 different vineyards in three general areas of the San Joaquin Valley. Zinfandel, Barbera, French Colombard, and Thompson Seedless varieties were studied (Table 1). At CSU Fresno, a replicated experiment was performed on Thompson Seedless, Zinfandel, and French Colombard. The treatment schedule is listed in Table 2. In addition, a second experiment focused on the role of surfactants with Cryolite on fluoride levels (Table 3). Treatments were applied at each vineyard using grower-supplied equipment; at CSU Fresno, applications were made with a single row over-the-vine boom sprayer. Insect populations were monitored frequently by growers and researchers during the growing season. No plots received applications of other non-fluoride containing products, but all other normal cultural practices were performed. At harvest, grapes from each treatment were made into wine. The wines were bottled and analyzed for fluoride by the Ion Selective Electrode method. The results from the 1993 research show that untreated grapes (Tl) had the lowest wine fluoride levels. In most cases, grapes treated at bloom and again 15 days later (T6) had the highest fluoride levels (Table 4). These results confirm earlier research that showed that wines which received Cryolite applications had significantly increased fluoride levels. The low rates applied at bloom, pre-bloom, and shatter caused small variations in fluoride levels, but the differences between treatments are very small. A replicated experiment at CSU Fresno showed no significant differences between any treatments (Table 5). In the surfactant study, applications of Cryolite with either a spreader or a sticker-spreader had no significant affect on wine fluoride levels. Most fluoride levels were exceptionally low in 1993, leading to the conclusion that the 6-pound full bloom rate will produce wine fluoride levels below the restrictive 1 ppm limit. Insect populations were monitored but counts remained low. No conclusions concerning efficacy can be made.

Influence of Windbreaks on the Vegetative and Reproductive Growth

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 conditions (control). Wind speed was reduced by up to 50%within the shelters, depending upon ambient wind velocity. 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 per vine. The specific weight (mg dry weight ? cm 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 internode length of non-sheltered vines. Total yield per vine for the windbreak treatment was 10%greater than the control in 1991, and 20%greater than the control in 1992. Yield differences were a result of increased berry number per cluster and cluster weight in the windbreak treatment. Fruit from the treatments did not differ significantly in berry weight, soluble solids content, titratable acidity, or pH at harvest in either season. Stomatal conductance and carbon assimilation rate was slightly greater for sheltered vines than for unsheltered vines. The results indicate that windbreaks augment vine capacity by increasing total leaf area and magnifying cluster weight fruit via their effects on vegetative growth and cluster weight.

Influence of Trellis-Training System and Rootstocks

The first year’s data from four-year-old Cabernet Sauvignon vines grown at the South Oakville Experimental Vineyard (OEV) comparing in-row vine spacings of 1. 2, and 3 meters showed average crop yields of 4.4, 3.7, and 2.7 tons/acre, respectively, when data of seven trellis systems and two rootstocks were averaged together. Closer vine spacing reduced the number of clusters per vine and slightly reduced the number of berries per cluster and cluster weight but had little effect on berry weight. The greater number of vines and clusters per acre, as a result of closer vine spacing, more than compensated for the fewer clusters per vine and berries set per cluster, accounting for the higher crop yield of closer vine spacing. Decreasing the distance between vines from 3 to 1 m significantly increased the level of titratable acidity and malic acid in fruit at harvest, but °Brix, pH, K, and anthocyanins in berry skins did not differ between vine spacing treatments. With wider vine spacing, there was an increase in the number of shoots, leaf area and pruning weight per vine, but a reduction in leaf area and pruning weight per meter of row length. With an increase in vine spacing from 1 m to 3 m there was a 33%decrease in average shoot length and also a reduction in number of leaves/shoot, internode length, primary and lateral leaf area per shoot and percentage of total leaf area accounted for by lateral leaves, resulting in a reduction in canopy density. The amount of leaf area per gram of fruit was also significantly less at 2 and 3 m vine spacing than at 1 m vine spacing. Data obtained in 1993 comparing the performance of 039-16 and 110R rootstocks grafted to Cabernet Sauvignon at vine spacings of 1, 2, and 3 m showed that 110R rootstock produced significantly more shoot growth, pruning weight, and crop yield than 039-16. UOR stock produced 20%more shoots per vine than 039-16 and shoot length was also about 20%longer on 110R grafted vines compared to 039-16. Pruning weights per vine of 110R stock was more than double that of 039-16. The yield/pruning weight ratio of vines on 110R stock was significantly less than 039-16 for each of the seven trellis systems. Cabernet Sauvignon on 110R stock produced 3.8 tons/ac compared to 2.87 tons/ac on 039-16. Wider vine spacing generally resulted in wines of lower pH and titratable acidity for all trellis systems. However, vine spacing had no significant effect on the level of ethanol and wine color. Duo-trio taste comparisons of wines made from the in-row vine spacings revealed that 1 m vine spaced wines could be distinguished from 3 m vine spaced wines for two of the four trellis systems, namely the GDC and Shoot Positioned Vertical trellises. Wines made from the V-trellis showed that 2 m vine spaced wines differed from 3 m vine spaced wines. In no case was the taste panel able to show significant differences between 1 and 2 m vine spaced wines.

Improvements and Replacements for Pre-Plant Soil Fumigation

High-pressure steam, hot air, hot water, and two years of solarization are ineffective fumigation replacements because heat cannot be distributed adequately through soil. Deeper placement and lower treatment rates with MB can deliver effective nematode control while reducing somewhat the MB volatilization, but control of weed seeds will be lost. Our soil drenching experiments show greatest potential as a replacement. Soil pest control and kill of old peach roots is equivalent to that attained with Telone or MB when 200 gal/ac Vapam is used. However, plant growth following 200 gal/ac does not keep pace with that of MB, Telone, or 100 gal/ac Vapam. One immediate spin-off from the drenching work is that growers already having drippers or planning to install them prior to replanting can use our drenching recipes today. Evaluation of the use of Roundup prior to tree and vine removal indicates that for Nemaguard rootstock the treatment can work well but not for plum roots. Our grape work involves Garlon, 2, 4-D, and Roundup. Rotation crops may have some value if complimentary methods of root kill become usable. Forty days and nights of flooding will not kill nematodes or old roots oiPrunus. Cabernet Sauvignon on Teleki 5C does not grow as well in a replant site as Cabernet on its own roots. It also did not respond as well to the Vapam drench (first year).

Evaluation of Microsprayers for Frost Protection in California Vineyards

Reduction in water use or increased water use efficiency are important concerns for wine grape growers. However, conservation of water must not reduce productivity, wine quality, or increase production costs. Targeted systems have been used in tree fruit and citrus production to provide frost protection while reducing the amount of water used. Potential benefits of a targeted system, such as microsprayers, for frost protection in vineyards include: reduced water use; less reservoir capacity is required; lower equipment costs for installation (smaller pumps and pipe); and less energy use. The purpose of this experiment was to investigate the use of microsprayers for frost protection in a commercial vineyard. The experimental site was a Chardonnay vineyard located near Los Alamos, CA. Plots were established during early March 1993 and data was collected from March 11, 1993 through May 20, 1993. The objectives of this experiment are to determine if an alternate method of frost protection (targeted microsprayer system) for California grapes is feasible and to determine if this method is less water consumptive than current practices demand. The microsprayer (Wade Pulsator?) being evaluated uses a pulsing action that produces larger diameter droplet sizes, while maintaining lower application rates than those found with conventional microsprayer design. This microsprayer produces a narrow band of water (approximately 0.6 meters wide) directed over the cordon of the vine. Microsprayers were installed in every vine row and mounted 0.56 meters above the cordon on every other stake, approximately 3.6 meters apart. A 2 ha block of microsprayers was compared to an adjacent sprinkler block. The sprinkler block is a typical design and installation for a commercial coastal vineyard. Sprinkler spacing is 15.6 meters X 12.8 meters, using a conventional impact type head and a 2.78 mm 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. 30 Data collected for the microsprayer and sprinkler blocks were bud temperature, air temperature, and relative humidity. Environmental conditions monitored outside the vineyard were air temperature, wind speed and direction, and relative humidity. Environmental data was collected with Omnidata data loggers using a series of thermocouples for bud temperatures(attached at bud locations) and Psychem 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. Radiational freezing events occurred on 28 April and 14 May 1993. Data collected on these dates suggests that microsprayers were as effective as overhead sprinklers for frost protection. A second year of data was collected during the spring of 1994 to further quantify the level of frost protection provided by microsprayers and the amount of water savings.

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

This report describes the 1993 results of continuing, large replicated trials in three San Joaquin Valley vineyards where we are studying the impact of three vineyard floor management systems on pests, weeds, and vine nutrient status. The experiments consisted of three main treatments: (1) an oat/vetch (two vineyards) or a merced rye/vetch mixture (one) vineyard planted in row middles, with row berms treated with preemergence herbicides, (2) the same as in 1, but the cover was cut and blown on berms for weed suppression (with only postemergence herbicides applied during late winter), and (3) cover crops were not planted, but row middles were clean-cultivated (control), and berms were treated with herbicides for weed suppression. An additional trial was established on a two-acre vineyard at the UC Kearney Agricultural Center. This vineyard included only treatments 2 and 3, and a treatment where we attempted to evaluate the impact of berm mulching on weed suppression without the use of preemergence and postemergence herbicides. During the 1993 season, the presence of cover crops did not affect the number of leafhoppers on vines in any of the four vineyards, but there were large differences between vineyards in the size of leafhopper infestations, levels of leafhopper-egg parasitism, and abundance and species composition of spiders. In general, two vineyards (7 and 10 years old) supported larger numbers of leafhoppers (11-15 nymphs per leaf) compared to the other two vineyards (more than 30 years old) where leafhopper numbers were lower than one nymph per leaf during the peak of the second generation. We do not really know the cause of these differences, but it appears that factors associated with vine age may have a significant impact on leafhopper abundance. The proportion of leafhopper eggs parasitized by Anagrus were also higher in the ‘young’ compared to ‘old’ vineyards, probably resulting from higher densities of leafhopper eggs in these vineyards. Parasitism in cover plots was similar to control plots, but there was a trend toward higher egg parasitism in cover plots during the second leafhopper generation. There were also large differences between vineyards, and between cover treatments within vineyards, in the abundance and species composition of spiders occurring on grapevines. In the ‘older’ vineyards, there were significantly higher populations of spiders on vines in cover crop and mulch plots compared to vines in control plots. Leafhoppers were too low in these vineyards for any effect to be observed during the 1993 season. The differences in spider abundance between cover and control treatments were only obtained in the old’ vineyards where spiders were predominantly of the web-building species. In the two young’ vineyards, where spiders were predominantly of the non-web-building (or hunting) species, we did not observe a significant effect of cover crops on spider abundance on vines. Initial 16 results from marking studies indicated that the cover crops are increasing the spider’s food abundance, and are providing an alternative foraging habitat for the spiders, but it is possible that not all spider species are similarly affected in this manner by the cover crops. Further results of these marking are pending. Results from experiments on weed suppression with dry mulch are variable. However, our studies and those conducted by C. Elmore in north coast vineyards indicated that yearly accumulation of biomass in vine rows should provide sufficient weed suppression to minimize the use of herbicides. The data on the nutritional status of vines showed that petiole tissue analysis for nitrate-nitrogen and potassium varied considerably between vineyards. In this first year of comparing fertilized and unfertilized plots (in the two ‘old’ vineyards) in the presence and absence of cover crops, we did not observe any significant impact of cover crops on nitrate-nitrogen status; but there was a trend toward higher potassium levels during veraision in the cover plots compared to control plots in the two ‘old’ vineyards. In the two ‘young’ vineyards, nitrate-nitrogen levels were reduced in the presence of cover crops, but no changes occurred in potassium levels. These effects were probably caused by factors related to the cover crop stand and weeds growing on berms. It is also possible that young’ vineyards are less competitive with cover crops than are ‘old’ vineyards. We are continuing to monitor changes in vine nutrient status which may not be reliably detected until the following year. Our initial budget for the three floor management systems indicates that the lowest cost is incurred in the absence of cover crops and when the commonly applied herbicides are used to control weed in the vine rows. We expect, however, that the overall benefit of using cover crops in vineyard production will be increased the cost of insecticides and fertilizers are incorporated into the cost/benefit analysis. Our findings are being disseminated to the scientific community and farmers in meetings and field days.

Wine Grape Canopy Management Practices in the San Joaquin Valley

Recent wine grape vine training and trellising studies in the San Joaquin Valley have demonstrated the influence of cordon height, foliage support wires, and quadrilateral training on vine yield, fruit composition, and wine quality. Concurrent studies in other districts have also demonstrated the beneficial effects of cluster exposure through leaf removal and other canopy management practices on grape composition and reduced fungal disease incidence. The purpose of this study was to determine the influence of several leaf removal techniques and shoot hedging on wine grape cultivars and trellis systems suitable to the San Joaquin Valley. Three leaf removal treatments — Hand, Window, and Hedge — and a check, no leaf removal were compared with French Colombard and Barbera. Leaf removal increased fruit zone light exposure in French Colombard temporarily due to its continued vigorous growth. This resulted in no fruit zone light environment differences at veraison and harvest. There were no significant fruit composition or bunch rot effects from any of the treatments in this cultivar. Hand leaf removal reduced vine yields, presumably due to berry loss from sun exposure soon after the treatment was imposed. Greater treatment effects were measured with Barbera. This could be explained by the more extreme and persistent effects of leaf removal in this less vigorous cultivar. Window leaf removal increased sunlight exposure through veraison while hand leaf removal was effective through harvest. However, this improved fruit exposure was not accompanied by any benefits in fruit composition, including soluble solids, pH, or anthocyanin content. The only treatment effects on fruit composition were reduced berry weight and titratable acidity in the Window and Hand treatments, respectively. The only positive effect was a reduction in bunch rot incidence from all of the leaf removal treatments as compared to Check. This included Hedge which did not improve fruit zone light environment at any time. This would suggest that hedging may provide adequate air circulation to reduce bunch rot while not changing the fruit zone light environment. Overall, the results further demonstrate that canopy management leaf removal has the potential to reduce bunch rot in the San Joaquin Valley. However, the rapid regrowth of vigorous French Colombard may reduce or eliminate this effect unless practiced at a later date during fruit ripening. The mechanical methods of Window and Hedge were as effective as Hand, cluster-region leaf removal in reducing rot. Thus, they would be preferable under San Joaquin Valley conditions due to economics. Leaf removal did not improve fruit composition as has been reported in cooler, coastal region studies. In fact, some leaf removal methods reduced berry weight, and titratable acidity in Barbera and yield in French Colombard. This was especially true of the more severe Hand leaf removal treatment where fruit exposure in this hot region caused berry burn. Thus, leaf removal canopy management practices in the San Joaquin Valley can be recommended for bunch rot control but are of questionable, if not detrimental, benefit to fruit composition and yield.

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

A study is being conducted to determine the water use or vineyard evapotranspiration (ET) of Chardonnay grapevines during 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 were grafted onto two different rootstocks (110R and 5C) to determine if there were differences in water use between the two. The rootstocks were planted in June of 1990 and Fall chip budded with the Chardonnay scion. Vineyard water use was determined by measuring soil water depletion and monitoring the addition of water via irrigation or measured rainfall. Soil water content was measured with a neutron probe (also called a hydroprobe or soil moisture gauge). Access tubes,. needed to measure soil water content, were placed at eight sites throughout the vineyard (four sites per rootstock). At each site six access tubes were places such that the soil water content in one quarter of an individual vine’s root volume could be quantified down to a depth of 3 m (approximately 10 ft) . The tubes were placed equidistant from one another: two tubes in the vine row, two tubes midway between rows and two tubes midway between the four tubes mentioned previously. The tubes also extended midway between v\Lnes within a row. The year 1992 represented the third growing season for this vineyard. Soil water content decreased rapidly early on in the growing season until the end of May. After this time soil water content remained constant until the end of October. The depth of water extraction from the soil extended down 1.3 m (4.25 ft). The constancy of the soil’s water content from June until October indicated that the water applied via irrigation equaled the amount of water used by the vineyard. The average seasonal water use of both rootstocks was 236 mm (9.3 inches) of water. This is equivalent to approximately 750 1 (200 gallons) of water per vine. The amount of water used by the vines supplied from the soil resevoir was 42%of the total amount used. Midday leaf water potentials were measured every two weeks during the season. Leaf water potential is a measure of a vine’s water status and would give an indication as to whether the vine experienced stress at any time. Of the eleven times measurements were taken, leaf water potential readings on nine dates indicated that the vines were not under stress (values were less negative than – 0.8 MPa or -8 bars) . However, on two of the dates leaf water potentials became more negative than -1.0 MPa. Values more negative than -1.0 MPa are associated with vine water stress in mature vines. It should be pointed out that on both of those dates ambient temperatures were greater than 32°C (90°F) and relative humidities were quite low. This information would indicate that irrigation amounts should have been increased during those periods when evaporative demand was greater than normal. One of the primary objectives of this study is to determine crop coefficients for vines grown in a cool climate during vineyard establishment. The crop coefficient for this vineyard started out at 0.5 and decreased thereafter until day of year 220 (approximately the first week in August) when the crop coefficient reached a minimum of 0.2. Subsequent to this date the crop coefficient increased and reached a maximum of 0.4 at the end of the growing season. The relatively high crop coefficient early in the season could have been due to the percolation of water below the depth of the access tubes (which would have been measured as vineyard water use) and the fact that a natural cover crop had been established during the winter months. The cover crop would have used a considerable amount of water until the vine rows started drying out. The increase in the crop coefficient from August until the end of the growing season was due to the continued growth of the vines up to November. An increase in the crop coefficient up to the end of the season has previously been reported for vines grown in the San Joaquin Valley during the second year of vineyard establishment.

Water Conservation in Wine Grape Production

An infrared thermometer (IRT) was used to schedule irrigation and impose selected levels of stress in two vineyards during the 1992 season. Cabernet Sauvignon vines in Paso Robles, CA and French Colombard vines in Ripperdan, CA were used in this project. Water was applied to drip irrigated vines only when IRT measurements indicated a certain level of water stress. If vines were below that stress level, water was withheld until stress increased to the selected level. Treatments were imposed from berry set to harvest. Water use was reduced during the berry set to harvest period by up to 50.3% and 39.0%, respectively for Cabernet Sauvignon and French Colombard vines. Treatments which exposed vines to moderate levels of stress for the entire berry set to harvest period produced the greatest reductions in water use. Irrigation scheduling treatments had no significant effect on yield or dormant pruning weight of Cabernet Sauvignon vines. However, growth and yield of French Colombard vines were significantly reduced by all programmed water stress treatments. Fruit maturity was generally advanced by increasing water stress but differences were often not statistically significant. These results are preliminary and several more years of data collection are required before equilibrium results are obtained. The Wade Manufacturing Pulsator microsprayer was subjected to further developmental testing in the Center for Irrigation Technology sprinkler testing laboratory to refine its application pattern. A commercial plot was established in a Chardonnay vineyard near Los Alamos, CA and field testing of the Pulsator occurred this spring. Analysis of data is not complete but it appears that the Pulsator microsprayer was as effective as overhead sprinklers for frost protection.