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.

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.