INTRODUCTION

Increased demand for premium red wine grape cultivars has resulted in a substantial increase in the number of acres of red wine grapes in California (Alder, 1997; Hilton, 1996; Striegler, 1996). For example, in 1992, 10,004 acres of Merlot existed (199 7 Grape Crop Acreage Report). By 1997, 32,883 acres of this cultivar had been planted, and it has been estimated that an even greater planting rate has occurred than is being reported (Bedwell 1998). Other red wine grape cultivars that have been planted e xtensively in recent years are Cabernet Sauvignon, Syrah, and Sangiovese. Much of the increased acreage of red wine grape cultivars has resulted from plantings in the San Joaquin Valley. Soil types and environmental conditions differ significantly between the San Joaquin Valley and coastal vineyard districts where these cultivars have more commonly been grown. Consequently, the success of "new" red wine grape cultivars in the San Joaquin Valley will require that information on cultural practices specific to this region be developed.

Leaf removal and shoot thinning are canopy management practices which are commonly used in coastal vineyard districts. These practices can reduce excessive canopy density (Bledsoe et al., 1988; Percival et al., 1994a; Reynolds et al., 1994a; Reynolds e t al., 1994c; Smart, 1985; Smith et al., 1988) increase yield (Bledsoe et al., 1988; Hunter et al., 1995; Percival et al., 1994b; Reynolds et al., 1994a; Reynolds et al., 1994c; Smart, 1988; Smith et al., 1988), reduce the incidence of disease (English et al., 1989; Gubler et al., 1987; Mayse et al., 1995; Percival et al., 1994b; Stapleton et al., 1992; Stapleton et al., 1995; Zoecklein et al., 1992) and insect pests (Stapleton, 1990), improve fruit composition (Bledsoe et al., 1988; Crippen and Morrison, 1986; Percival et al., 1994b; Zoecklein et al., 1992; Zoecklein et al., 1998), and increase wine quality (Reynolds et al., 1994b; Reynolds et al., 1996; Smart et al., 1990).

Little information is available in the technical literature on the use of leaf removal and shoot thinning under San Joaquin Valley conditions. Therefore, the purpose of this experiment is to evaluate the response of six red wine grape cultivars to basa l leaf removal and shoot thinning under warm climate conditions.

MATERIALS AND METHODS

This experiment is being conducted in the California State University, Fresno campus vineyard. Harmony rootstock were planted in San Joaquin Loam soil in 1991 and grown for two seasons. Rootstocks were field-grafted in 1993 to selected scion cultivars. Row orientation is east-west and vineyard spacing is 7 feet X 12 feet (Vine x Row). Irrigation is supplied to vines through a drip system. The trellis system consists of a six-foot stake at each vine with a cordon wire at 40 inches and a foliage wire at 58 inches above the soil surface. Vines are trained to a bilateral cordon and fruiting wood is retained as two-bud spurs. Vines are balance pruned in this experiment to retain 16 buds per pound of dormant cane prunings (Jordon et al., 1981). All other cul tural practices (except those under evaluation) were standard for the San Joaquin Valley.

Treatments used in the experiment were cultivar and canopy management practices. Cultivars under evaluation were Syrah, Sangiovese, Cabernet Sauvignon, Zinfandel, Barbera, and Merlot. All cultivars are being evaluated for their use in production of red table wines. Canopy management practices used were no canopy manipulation (control), shoot thinning, leaf removal, and shoot thinning plus leaf removal. Shoot thinning is accomplished before bloom when shoots are approximately 6 inches in length by remov ing all non-count shoots. This commonly consisted of removing secondary shoots, tertiary shoots, and shoots from base buds at each spur position, as well as any shoots arising directly from the cordon. Leaf removal consists of the removal of all main and lateral leaves from the shoot base to one node past the apical cluster at two weeks post bloom (berry set).

The experimental design used is a randomized complete block. There are four blocks and experimental plots consist of two vines. One hundred berries were collected from the apex of representative clusters within each treatment and replication just prior to harvest. Berry samples were stored at 34°F until analysis. All samples were analyzed within two days of sampling. At the time of analysis, berries were crushed and the resulting juice filtered through cheesecloth. Soluble solids were measured using an Abbe refractometer (Lecia Mark II). A Corning pH/Ion analyzer (model 350) was used to determine titratable acidity, and pH (Zoecklein et al., 1995). Berry color was determined by measurement of anthocyanin content of fruit (Kliewer, 1977).

At harvest, yield and cluster number were determined. During the dormant season vines were pruned, and one-year wood was collected for each vine and weighed with a field spring-loaded scale. All data were organized and subjected to a factorial analysis of variance, with cultivar and canopy managment technique as factors (Little and Hill, 1978). Means were separated by Duncan's multiple range test at the five-percent level.

RESULTS AND DISCUSSION

Yield and components of yield were significantly affected by both cultivar and canopy management (Table 1). Barbera produced the highest yield while Zinfandel and Merlot produced the lowest yield. Yield of Zinfandel was impacted by incidence of summer bunch rot complex. High yield was also recorded for Syrah and Sangiovese. Cabernet Sauvignon produced good yield but was not to the level of Barbera, Syrah, and Sangiovese. Clusters per vine were highest for Syrah, Cabernet Sauvignon, and Barbera. Sangiov ese, Merlot, and Zinfandel had fewer clusters per vine than the other cultivars. The cluster number obtained for Zinfandel was reduced due to removal of clusters affected by summer bunch rot complex.

Cluster weight was highest for Sangiovese, Barbera, and Zinfandel. Syrah, Cabernet Sauvignon, and Merlot had significantly smaller cluster weight than the other cultivars. Berry weight displayed a considerable degree of diversity. Each cultivar had a d istinct berry weight which was statistically significant from the other cultivars. Berry weight was greatest for Barbera and lowest for Merlot. Grouping of cultivars was again observed for the number of berries per cluster. Syrah, Sangiovese, and Merlot h ad more berries per cluster than Cabernet Sauvignon, Zinfandel, or Barbera.

Canopy management effects on yield and components of yield were limited to the shoot thinning treatment (Table 1). Leaf removal did not differ significantly from the control treatment in any of the yield parameters measured. On the other hand, shoot th inning and the combined leaf removal plus shoot thinning treatment were significantly different than the control treatment for all parameters other than berry weight. Shoot thinning reduced yield and clusters/vine while increasing the cluster weight and b erries per cluster.

Cultivar had a significant impact on fruit composition (Table 2). Syrah, Cabernet Sauvignon, Zinfandel, and Merlot had a higher percentage soluble solids than Sangiovese and Barbera. The pH of berries was greatest for Syrah and lowest for Cabernet Sau vignon and Barbera. Titratable acidity was significantly higher for Barbera than for other cultivars. Cabernet Sauvignon berries had greater color or anthocyanin content than berries from the other cultivars. Canopy management treatment did not significan tly impact fruit composition.

Growth was significantly affected by cultivar and canopy management (Table 3). However, the impact of cultivar was greater than that of canopy management treatment. Merlot had fewer shoots per vine than Sangiovese, Cabernet Sauvignon, or Barbera. Pruni ng weight or vine capacity was highest for Syrah and Cabernet Sauvignon. Merlot and Sangiovese produced the lowest pruning weight. Nodes retained reflected pruning weight data since vines were balance pruned. Canopy management effects on growth were limit ed to shoots per vine. Shoot thinning reduced shoots per vine but did not significantly reduce pruning weight.

CONCLUSIONS

This experiment is continuing; therefore the data presented represents a report of work in progress. The results to date can be summarized as follows:

1. Cultivar had a greater impact than canopy management treatment.
2. Syrah, Cabernet Sauvignon, and Barbera have displayed the most promising data. Syrah and Barbera had high yield, good vegetative growth, and acceptable fruit composition. Cabernet Sauvignon had good yield, good vegetative growth and the best fruit co mposition. Observations on cultivars whose performance has been less promising are also important. Sangiovese produced high yield due to large cluster size. However, soluble solids accumulation was delayed somewhat and vegetative growth was poor. It appears this cu ltivar requires cluster thinning. Clonal selection may alleviate this concern. Zinfandel yield was negatively impacted by the summer bunch rot complex. The incidence of this disease appeared to be uniform across canopy management treatments (no apparent e ffect of leaf removal). Merlot produced low yield, poor vegetative growth and good fruit composition.
3. Shoot thinning reduced shoots per vine, clusters per vine, and yield but did not affect fruit composition or pruning weight.
4. Leaf removal had no significant effect on yield, fruit composition, or growth under the conditions of this study.

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CALIFORNIA AGRICULTURAL TECHNOLOGY INSTITUTE - CATI
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California State University, Fresno