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Larry E. Williams, Rudy A. Neja, Jewell L. Meyer, Lori A. Yates, and Eddie L. Walker

1 Associate Professor, Univ. of California, Davis. 2 Farm Advisor, Riverside County. 3 Extension Specialist. 4 Extension Statistician. 5 Vineyard Manager. The cost of publishing this paper was defrayed in part by the payment of page charges

Open access

James A. Schrader, Diana R. Cochran, Paul A. Domoto, and Gail R. Nonnecke

. Nursery-grown vines of ‘Arandell’, ‘Corot noir’, ‘Frontenac’, ‘La Crescent’, ‘Marquette’, ‘MN 1189’, ‘MN 1200’, ‘MN 1220’, ‘MN 1235’, ‘MN 1258’, ‘Petit Ami’, and ‘St. Croix’ were received from Double A Vineyards, Inc. (Fredonia, NY) as part of the NE-1020

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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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Bruce P. Bordelon and Jill Hubertz

In a previous study to determine the feasibility of using herbicide desiccated cover crops for weed suppression during vineyard establishment, we found that weed suppression is excellent for about 6 to 8 weeks after desiccation in fall-planted rye. By the end of the season, however, weed growth in rye plots was similar to weedy control plots. Vine growth was reduced in rye plots compared to weed-free bare ground plots. Because of the experimental design, no follow-up weed control was performed in the rye plots and weeds eventually became well-established. So, it was impossible to determine if reduced vine growth was due to weed competition or allelopathy from the rye residues. A second study was conducted to determine the effects of follow-up weed control (with glyphosate) in fall-planted rye plots and weedfree bare ground plots. Results indicate that vine shoot number, shoot length, leaf area, and top growth dry weight was greatest in weedfree bare ground, less, but not significantly so in rye with follow-up weed control, and significantly less in rye without follow-up weed control. Root dry weight was reduced in rye with and without follow-up weed control compared to weedfree bare ground. Root dry weight was reduced 37% in rye with follow-up weed control and 63% in rye without follow-up weed control compared to weedfree bare ground. These results suggest that weed competition is not the primary cause of vine growth reduction in herbicide desiccated rye cover crops, so there is likely allelopathic effects of the rye residues on grapevines, which would limit using rye as a desiccated cover crop during vineyard establishment. However, there may be some value in using rye in established vineyards to reduce vigor.

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N.S. Lang, R. Smithyman, L. Mills, R.L. Wample, J. Silbernagel, and E.M. Perry

Blackleaf (a.k.a. chocolate leaf) is of worldwide concern in Vitis due to its negative impact on fruit ripening, yield reduction and overall stress on grapevines. Research suggests blackleaf is induced by high levels of UV radiation and overall light intensity, which induce color changes (purple-brown-black) in exposed leaves, resulting in >50% reduction in photosynthesis. The ability to detect blackleaf symptoms before expression can provide insight into metabolic stresses and the possibility of the use and/or timing of management practices to reduce its impact. Remotely sensed imagery and spatial analysis may elucidate reflectance-related processes and symptoms not apparent to the un-aided eye. In this research we mapped canopy growth (leaves/shoot and shoots/vine), metabolic triggers (photosynthesis, leaf water potential, soil moisture), and percent blackleaf expression within vineyards using global positioning system (GPS), infrared gas analyzer, and digital remotely-sensed images. Each image and data record was stored as an attribute associated with specific vine location within a geographical information system (GIS). Spatial maps were created from the GIS coverages to graphically present the progression of blackleaf across vineyards throughout the season. Analysis included summary statistics such as minimum, maximum, and variation of green reflectance, within a vineyard by image capture date. Additionally, geostatistics were used to model the degree of similarity between blackleaf values as a function of their spatial location. Continuing research will be aimed at identifying spectral characteristics of early season stresses due to UV light, water stress, and reduced photosynthetic capacity. Spatial relationships between early season stress and later blackleaf expression will be assessed using joint spatial dependence measures. Overall, information obtained through digital image and spatial analysis will supplement site level information for growers.

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L.E. Williams and F.J. Araujo

A study was conducted to compare three measurements of determining water status of grapevines (Vitis vinifera L.) in the field. Predawn leaf water potential (ΨPD), midday leaf water potential (Ψl), and midday stem water potential (Ψstem) were measured on `Chardonnay' and `Cabernet Sauvignon' grapevines grown in Napa Valley, California late in the 1999 growing season. Both cultivars had been irrigated weekly at various fractions (0, 0.5, and 1.0 for `Chardonnay' and 0, 0.5, 0.75, and 1.5 for `Cabernet') of estimated vineyard evapotranspiration (ETc) from approximately anthesis up to the dates of measurements. Predawn water potential measurements were taken beginning at 0330 hr and completed before sunrise. Midday Ψl and Ψstem measurements were taken only between 1230 and 1330 hr. In addition, net CO2 assimilation rates (A) and stomatal conductance to water vapor (gs) were also measured at midday. Soil water content (SWC) was measured in the `Chardonnay' vineyard using a neutron probe. Values obtained for ΨPD, Ψl, and Ψstem in this study ranged from about -0.05 to -0.8, -0.7 to -1.8, and -0.5 to -1.6 MPa, respectively. All three measurements of vine water status were highly correlated with one another. Linear regression analysis of Ψl and Ψstem versus ΨPD resulted in r 2 values of 0.88 and 0.85, respectively. A similar analysis of Ψl as a function of Ψstem resulted in an r2 of 0.92. In the `Chardonnay' vineyard, all three methods of estimating vine water status were significantly (P < 0.01) correlated with SWC and applied amounts of water. Lastly, ΨPD, Ψl, and Ψstem were all linearly correlated with measurements of A and gs at midday. Under the conditions of this study, ΨPD, Ψl, and Ψstem represent equally viable methods of assessing the water status of these grapevines. They were all correlated similarly with the amount of water in the soil profile and leaf gas exchange as well as with one another.

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Sanliang Gu, Carlos H. Crisosto, R. Scott Johnson, Robert C. Cochran, and David Garner

Fruit from 8 `Hayward' kiwifruit vineyards in central California were harvested at 2 week intervals after soluble solids content (SSC) reached 6% and subjected to 4 and 6 months of storage at 0°C in an ethylene free environment. Fruit characteristics at harvest and postharvest performance varied considerably among locations. Fruit stored for 6 months had the same fresh weight, less flesh firmness and higher SSC, than the 4 months storage. Later harvested fruit had greater fruit flesh firmness and higher SSC after storage. SSC after storage was predictable based on ripe soluble solids content (RSSC) at harvest. Summer pruning reduced while soil nitrogen application increased fruit SSC.

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C.L. Gupton

A muscadine vineyard planted at McNeil, Miss., in 1990 included 23 cultivars and a planting in 1992 included nine cultivars. Each entry was evaluated for eight useful traits over 4 years. The regressions of certain traits on others were performed to determine relationships that might be useful in selecting for valuable traits such as phyto-chemicals in seed. Ranges among cultivars for the traits were: harvest date—20 days, yield—33 kg per vine, berry weight—11.2 g, percent dry scar—38, °Brix—5, pH—0.5, seed per berry—1.2 and seed weight—5.5 g. The best relationship was between berry weight and seed weight.

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Stephen J. Stringer, Donna A. Marshall, James M. Spiers, and Blair J. Sampson

Muscadines are grapes indigenous to the Southeastern United States, and they are highly prized for their unique fruity flavors. Factors including skin color, berry size, skin thickness, flower type, productivity, etc., vary among muscadine grape cultivars, making some cultivars more desirable for fresh market while others are better suited for processing and prodction of juice, jelly, and wine. A muscadine grape research vineyard was established in McNeil, Miss., in 1992 containing 37 named cultivars and numerous breeding lines. Performance of these cultivars was evaluated in 2001–2003 and results of these trials are presented.

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Justin R. Morris

Interest in grape juice has risen as the public becomes more aware of natural foods and the specific evidence of healthful benefits of grapes. Among major preharvest conditions that influence quality of grape juice are climate, soil, cultivar, vineyard management, and maturity. Each of these factors exerts its own influence, but complex interactions among these factors must be recognized. For mechanically harvested juice grapes, cultivar takes on special importance to quality and yield as do the production system, harvest machines, postharvest handling systems, and processing method. Grape juice composition has been extensively studied, and production and processing methods have improved over the years. The following discussion deals with developments in grape juice production.