More than 50% of the 3.6 million tons of winegrapes grown in California each year come from the SJV. Even though SJV grapes are a staple of California’s wine industry, the increasing costs of labor present an economic risk for SJV winegrape vineyards. The cash market price for commercially acceptable winegrapes in Crush District 13 of California averaged $279.97/ton (California Department of Food and Agriculture, 2012) with an average yield of 14.7 tons/acre, while total operating costs were $5007.00/acre (Verdagaal et al., 2008). Therefore, winegrape growers are looking for ways to reduce their labor costs, while maintaining yield and fruit quality parameters as demanded by winery contracts.
With narrow profit margins, the majority of the growers do not apply the principles of canopy management because of cost and time constraints (Terry and Kurtural, 2011). To remain profitable, growers tend to retain too many nodes during dormant pruning, resulting in out-of-balance vines with less than desirable fruit quality at the farm gate. Many growers preprune their vines with a mechanical prepruner to a bearing surface height of 8 inches (≈250% of the nodes required by balanced pruning) and return to adjust shoot numbers at Eichhorn–Lorenz (E–L) growth stages 17 to 19 (Coombe, 1995). However, adjusting shoot numbers manually is expensive and requires rigorous crop estimation. The practice of mechanical prepruning and manual shoot removal leads to unbalanced vines because of time constraints to adjust the shoot numbers. This has become a greater problem as the labor supply declined. Unbalanced vines tend to develop large leaf canopies with a high water demand and an undesirable microclimate leading to a lower proportion of fruitful buds in subsequent seasons and fruit of inferior quality and a lower price. It has previously been shown that vine balance can be achieved in ‘Syrah’ (Vitis vinifera) grapevine grown in the SJV when they were mechanically box-pruned to a 4-inch hedge and shoots thinned to a density of seven count shoots per foot of row, and irrigation was reduced to 50% of daily evapotranspiration (ETo) between fruit set and veraison (Terry and Kurtural, 2011). Bates and Morris (2009) recently reported a 56% to 80% per acre decrease in labor costs for ‘Concord’ grapevine (Vitis labrusca) when mechanical canopy management was used compared with traditional HP to produce a marketable crop.
A key component of the efficient use of the mechanical canopy management is to achieve balanced cropping along with a favorable canopy microclimate (Morris, 2007; Terry and Kurtural, 2011). Balance in vineyards can be measured with the Ravaz index. The Ravaz index is not a direct measurement but a ratio between vegetative and reproductive measurements expressed as crop yield per dormant pruning weight with optimum values between 5 and 10 (Kliewer and Dokoozlian, 2005). Balanced cropping aims to achieve equilibrium between vegetative and reproductive growth of the grapevine, and thus ensures sustainable vineyard production. Canopy management, whether applied by conventional or mechanical methods, may include the following practices: 1) dormant pruning, 2) shoot thinning, 3) shoot positioning, 4) cluster thinning, 5) leaf removal, and 6) hedging/skirting. The effects of various canopy management practices are varied depending on the macroclimate, cultivar, and irrigation requirement of a vineyard. The effects may include reduced vegetative growth (Smart, 1985, 1988), a favorable light regime in the defined fruit zone (Dokoozlian and Kliewer, 1995; Gladstone and Dokoozlian, 2003), enhanced fruit composition (Kurtural et al., 2006; Petrie and Clingeleffer, 2006; Smart, 1988; Terry and Kurtural, 2011), and balanced vines for sustained commercial production (Morris, 2007; Reynolds and Wardle, 1993; Terry and Kurtural, 2011).
While there have been numerous attempts to quantify the labor costs associated with mechanical canopy management in California, there are no published reports of replicated trials in this area. The objective of this study was to compare the viticulture and economic characteristics of traditional HP, mechanical prepruning plus manual shoot thinning, and mechanical box-pruning plus mechanical shoot thinning in the SJV of California. The measurements used to quantify the effects of these three canopy management practices included canopy architecture and microclimate, yield components, fruit composition, and labor costs.
Bates, T. & Morris, J. 2009 Mechanical cane pruning and crop adjustment decreases labor costs maintains fruit quality in New York ‘Concord’ grape vineyards HortTechnology 19 247 253
California Department of Food and Agriculture 2012 Grape crush report Final 2011. 1 Apr. 2012. <http://www.nass.usda.gov/Statistics_by_State/California>
Dokoozlian, N.K. & Kliewer, W.M. 1995 The light environment within grapevine canopies I. Description and seasonal changes during fruit environment Amer. J. Enol. Viticult. 46 209 218
Flaherty, D.I., Christensen, D.I. & Lanni, T. 1992 Grape pest management. Univ. of California Agr. Natural Resources. Bul. 3343
Giusti, M.M. & Wrolstad, R.E. 2001 Characterization and measurement of anthocyanins by UV-visible spectroscopy, p. F1.2.1–F1.2.13. In: R.W. Wrolstad (ed.). Current protocols in food analytical chemistry. Wiley, New York
Gladstone, E.A. & Dokoozlian, N.K. 2003 Influence of leaf area density and trellis/training systems on the microclimate within grapevine canopies Vitis 42 123 131
Harbertson, J.F., Picciotto, E.A. & Adams, D.O. 2003 Measurement of polymeric pigments in grape berry extract and wines using a protein precipitation assay combined with bisulfate bleaching Amer. J. Enol. Viticult. 54 301 306
Keller, M. 2010 The science of grapevines: Anatomy and physiology. Academic Press, Burlington, MA
Keller, M., Smithyman, R.P. & Mills, L.J. 2008 Interactive effects of deficit irrigation and Cabernet Sauvignon grapevines in an arid climate Amer. J. Enol. Viticult. 59 221 233
Kliewer, W.M. & Dokoozlian, N.K. 2005 Leaf area/crop weight ratios of grapevines: Influence of fruit composition and wine quality Amer. J. Enol. Viticult. 56 170 181
Kurtural, S.K., Taylor, B.H. & Dami, I.E. 2006 Effects of pruning and cluster thinning on yield and fruit composition of “Chambourcin” grapevines HortTechnology 16 233 240
Kurtural, S.K & O’Daniel, S.B. 2008 Crop estimation in vineyards. Univ. of Kentucky Coop. Ext. Serv. Bul. HO-86
Levene, H. 1960 Contributions to probability and statistics. Stanford University Press, Palo Alto, CA
Petrie, P.R. & Clingeleffer, P. 2006 Crop thinning, grape maturity and anthocyanins concentration: Outcomes from irrigated Cabernet Sauvignon in a warm climate Aust. J. Grape Wine Res. 12 21 29
Reynolds, A.G. & Wardle, D. 1993 Yield component path analysis of Okanagan Riesling vines conventionally pruned or subjected to simulated mechanical pruning Amer. J. Enol. Viticult. 44 173 179
Smart, R.E. 1985 Principles of grapevine microclimate manipulations with implications for yield and quality: A review Amer. J. Enol. Viticult. 36 230 239
Smart, R.E. & Robinson, M. 1991 Sunlight into wine: A handbook for winegrape canopy management. Winetitles, Adelaide, Australia
Terry, D.B. & Kurtural, S.K. 2011 Achieving vine balance of Syrah with mechanical canopy management and regulated deficit irrigation Amer. J. Enol. Viticult. 62 426 437
U. S. Department of Agriculture 2011 Soil survey staff Official soil series descriptions. 1 Apr. 2011. <http://soils.usda.gov/technical/classification/osd/index.html>
Verdagaal, P., Klonsky, K.M. & De Moura, R.L. 2008 Sample costs to establish a vineyard and produce winegrapes ‘Cabernet Sauvignon’ Crush District 11 of San Joaquin and Sacramento counties. Univ. of California Coop. Ext. Serv. Bul. GR-VN08
Waterhouse, A. 2002 Determination of total phenolics, p. 11.1.1–11.1.8. In: R.W. Wrolstad (ed.). Current protocols in food analytical chemistry. Wiley, New York
Zabadal, T.J., Vanee, G.R., Dittmer, T.W. & Ledebuhr, R.L. 2002 Evaluation of strategies for pruning and crop control of Concord grapevines in southwest Michigan Amer. J. Enol. Viticult. 53 204 209