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R.K. Striegler and D.R. Wineman

Selected rootstocks were evaluated for four seasons in a Zinfandel vineyard located in the northern San Joaquin Valley of California. The vineyard was drip-irrigated and vineyard spacing was 2.1m × 3.3m (vine × row). A two-wire vertical trellis system was used and row orientation was east to west. Vines were trained to a bilateral cordon and spur-pruned. Rootstocks included in the study were: AxR #1, Freedom, Harmony, Kober 5BB, and Teleki 5C. Vines grafted on AxR #1 rootstock were considered to be the control treatment.

A randomized complete block experimental design was used. There were six blocks and plots consisted of five vines. Data collected included yield, components of yield, fruit composition, bloom petiole nutrient content, shoot number, and pruning weight.

After the initial season, yields were consistently highest for vines grafted on Freedom rootstock, with yields only slightly lower on AxR #1 rootstock. Significantly lower yields were recorded for vines grafted on Kober 5BB and Teleki 5C. Rootstock did not have a consistent effect on fruit composition. Shoots/vine and shoots/meter of canopy were not significantly effected by rootstock. Dormant pruning weight was highest for Freedom and lowest for Kober 5BB.

These results suggest that rootstock selection can influence vineyard productivity in the northern San Joaquin Valley. Continued research is needed to determine long term effects of the rootstocks used in this study.

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G.T. Berg and R.K. Striegler

The availability and cost of labor are important concerns for many California wine grape growers. Greater state and federal labor regulations, increased grower liability, increased efforts to control illegal immigration, and mandated increases in the minimum wage are causing growers to investigate production systems that may reduce labor requirements and costs. The purpose of this experiment was to determine the influence of training system and mechanization on vegetative growth, yield, fruit composition, labor requirements, and production costs for wine grapes grown in the San Joaquin Valley of California. Barbera vines grafted on Freedom rootstock were used in the experiment. Treatment variables examined were training system (bilateral cordon, non-positioned vs. bilateral cordon, vertical shoot positioned) and pruning method (hand vs. machine pre-pruning with hand follow-up). The experimental design used was a randomized complete block with data analyzed as a factorial. There were five blocks and all treatment combinations were evaluated. Data were collected during the 1994 and 1995 seasons for vegetative growth, yield, fruit composition, pruning labor requirements, and machinery performance. Few treatment effects were observed on vegetative growth, yield, and fruit composition during the course of this study. When significant differences were noted for these parameters, training system had a greater impact than pruning method. In contrast, labor requirements and production costs displayed a significant response to pruning method. Machine pre-pruning reduced pruning labor requirements from 41 man-hours per acre to 24–28 man-hours per acre per year. Pruning labor requirements were reduced by ≈40% and the costs associated with pruning were reduced by ≈30%.

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R.K. Striegler and G.T. Berg

Grape growers in the southern San Joaquin Valley of California are increasingly concerned about production costs. Reduced demand for wine grapes from this district has resulted in low prices and a decline in grower profitability in recent years. Minimal pruning is a low-cost production system that was developed in Australia more than 20 years ago. This system offers complete mechanization of pruning and harvesting. In general, there is little information available on the use of minimal pruning in California vineyards. The propose of the experiment was to compare the effects of hand and minimal pruning on growth, yield, and fruit composition of `Ruby Cabernet' grapevines. This experiment was conducted in a commercial vineyard near Huron, Calif., during the 1993 and 1994 seasons. Minimally pruned vines had more shoots and fewer mature nodes than hand-pruned vines. Yield and components of yield were also significantly altered by pruning method. Minimal pruning produced the highest yield and number of clusters, while hand-pruning resulted in larger berry weight, cluster weight, and number of berries per cluster. Pruning method did not significantly affect fruit composition.

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R.K. Striegler, G.T. Berg, M. Rothberg and D. Zoldoske

Using subsurface drip irrigation (SDI) is increasing in California vineyards. Reports from growers indicate increased yield, increased water-use efficiency, enhanced soil pest control, and reduced canopy disease pressure for SDI when compared to aboveground drip irrigation (AGDI). However, little information is available in the literature regarding this relatively new irrigation technology for grapes and other perennial crops. A long-term trial was established to evaluate the performance of AGDI and SDI in a mature `Thompson Seedless' raisin vineyard. Portions of a furrow irrigated vineyard block were converted to AGDI and SDI before budburst in 1993. Vine performance, water use, and irrigation system performance data are being collected. As part of this trial, changes in root distribution were examined after harvest in Nov. 1995. Treatments included AGDI, SDI, and furrow irrigation. Root distribution was quantified using the trench profile method. Trenches were opened perpendicular to the row and ≈30 cm from the vine. Roots were mapped along the profile wall using a 1 × 1 m frame, which was divided into one hundred 10 × 10 cm sections. Roots were counted and categorized into four size classes: small (<2 mm), medium (2 to 5 mm), large (5 to 12 mm), and very large (>12 mm). Root distribution differed significantly for AGDI, SDI, and furrow irrigation. The type of irrigation used had the greatest impact on small roots. SDI had more small roots and total roots than AGDI or furrow irrigation. High root densities were observed near the emitter under AGDI and SDI. In addition, both drip irrigation treatments had higher root density near the soil surface than furrow irrigation. Root intrusion was not observed in the SDI treatment.

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R.K. Striegler, M.A. Mayse, U. O'Keefe and D.R. Wineman

Consumer concerns about pesticide residues and environmental degradation are having a significant impact on the California grape industry. Growers are using a variety of practices, from integrated pest management to certified organic production, to reduce the amount of pesticides and other synthetic inputs used in vineyards. This experiment was established to test selected sustainable cultural practices in a mature `Thompson Seedless' vineyard. Treatments included in the experiment were row middle management (cultivated vs. perennial legume cover crop) and nitrogen fertilization (compost vs. synthetic). Vine nutritional status, yield, fruit composition, pruning weight, and population levels of the variegated leafhopper were monitored each season (1992–1994). In addition, efforts were expanded during the 1994 season to include assessment of spider, herbivorous mite, and beneficial arthropod densities. Conventional cultural practices (cultivation and synthetic fertilizer) produced the highest yields during the 1992 and 1993 seasons. This result may have been due to the nutritional status of vines, which was generally better for the cultivation and synthetic fertilizer treatment, especially in 1992. In 1994, significant treatment effects on yield were not observed, indicating that legume cover crop plots had become fully established. Sustainable cultural practices had little impact on growth, fruit composition, or insect pest pressure. `Thompson Seedless' grapes were grown for three seasons without the use of insecticides or herbicides. Vine diseases were managed by cultural practices and application of sulfur.

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R.K. Striegler, J.R. Morris, P.M. Carter, J.R. Clark, R.T. Threlfall and L.R. Howard

A muscadine grape (Vitis rotundifolia) planting was established in 1996 at the Southwest Research and Extension Center in Hope, Ark., to provide information on the performance of muscadine grape cultivars in a region where cold hardiness is not a major limitation. This research evaluated harvest parameters, fruit and juice quality, and nutraceutical potential of selected muscadine cultivars grown in southwestern Arkansas. The cultivars evaluated were `Black Beauty', `Carlos', `Cowart', `Doreen', `Early Fry', `Fry', `Granny Val', `Ison', `Jumbo', `Late Fry', NC67A015-17, NC67A015-26, `Nesbitt', `Scarlett', `Southern Home', `Sterling', `Sugargate', `Summit', `Supreme', and `Tara'. Muscadine cultivars differed in productivity and fruit quality. In 2002 and 2003, juice was produced from `Carlos', `Granny Val', `Ison', `Nesbitt', `Southern Home', `Summit', and `Supreme' grapes. `Black Beauty' was also produced into juice in 2003. In 2002, `Nesbitt' grapes had the highest juice yield, 520 L·t–1 (124.6 gal/ton). `Ison' and `Supreme' juice had the highest soluble solids level. In 2003, `Granny Val' grapes had the highest juice yield, 551 L·t –1 (132.0 gal/ton). `Southern Home' juice had the highest soluble solids. The press materials of muscadine grapes were a potential source of high levels of nutraceutical compounds. Dried seeds had the highest total phenolic and oxygen radical absorbance capacity (ORAC) levels followed by the dried skins, the grapes, and then the juice. The skins of the black cultivars had the highest total anthocyanins level. `Supreme' seeds had the highest total phenolic and ORAC levels while `Ison' skins had the highest total anthocyanin levels. Based on yield, harvest, and juice quality, cultivars recommended to growers in southwestern Arkansas and other areas with a similar climate include `Black Beauty', `Carlos', `Fry', `Granny Val', `Nesbitt', `Southern Home', `Summit', and `Supreme'.

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N.O. Maness, D.R. Chrz, K. Striegler, I Wahem and T.G. McCollum

Fresh strawberries are highly perishable commodities, and berry quality at harvest delimits their potential shelf life. We are conducting harvest quality evaluations for seven commercially available cultivars. Seven different fruit characteristics were chosen to assess cultivar performance during the early, middle and late phases of the picking season: marketable berry yield, berry weight, berry firmness, berry color (“a” value), percept soluble solids, titratable acidity (percent citric acid) and the ratio between soluble solids and titratable acidity. Marketable berry yield, berry weight and berry firmness varied substantially between cultivars. A few differences were observed between cultivars for berry color. Berry flavor, as evidenced by the ratio between soluble solids and acidity, was also apparently different between cultivars with three of the seven cultivars consistently exhibiting higher ratios. The relationship of each measured parameter to quality will be discussed.