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grapegrowing agement programs. The risks associated with this material are the viticultural risks described above. The legal use of gibberellin, like all registered growth-enhancing chemicals, requires the written recommendation of a licensed pest control advisor. With their guidance you can avoid the risks and achieve the benefits of this material. Labeled application concentrations for specific winegrape varieties and sprayer tank volumes are given in Table II. These solutions will elongate clusters and minimize bunch rot with negligible undesirable side effects when applied during the cluster elongation period. For consistent results, thoroughly wet the entire foliage with the specified solution. Gibberellin is only one component of a comprehensive bunch rot-management program for tight-cluster wine grape varieties. To ensure minimum bunch rot, use gibberellin with additional practices and materials that effectively address the other components of the disease triangle. Conclusion Gibberellin application is a low-cost, efficacious method to minimize bunch rot in compact clusters, especially when used in conjunction with vineyard management practices that optimize air movement in the fruit zone and reduce bunch rot inoculum. Gibberellin must be applied at the proper time and in the proper concentration to avoid undesirable side effects related to fruit yield both during the year of application and the following year. Application concentration is varietyspecific because varieties differ in their sensitivity to gibberellin. Properly applied foliar applications of gibberellin will enhance normal physiological processes during rapid cluster elongation. Apply gibberellin only with the assistance and written recommendation of a pest control advisor. PWV The author is grateful to John Baranek for his advice and guidance regarding gibberellin application for bunch rot control in wine grapes and also extends many thanks to Mid Valley Agricultural Services and Barbara Grant. This article is dedicated to the memory of Mike Vail, one of California's finest viticulturists. Bibliography 1.Agrios, G.N. 1988 Plant Pathology. San Diego: Academic Press. 2.Baranek, J. Personal communication. 3.Baranek, P. "Gibberellin – a management tool in wine grapes." 1980 pp. 64-75. In Dinsmoor, A.W. (Ed.). University of California, Davis Grape Centennial Symposium. 4.Collins, C. and B. Rawnsley. 2008 "Effect of gibberellic acid and paclobutrazol on the incidence of primary bud necrosis in cv. Syrah." Am. J. of Enol. & Vit. 59: 83-87. 5.English, J.T., C.S. Thomas, J.J. Marois, and W.D. Gubler. 1989 "Microclimates of grapevine canopies associated with leaf removal and control of Botrytis bunch rot." Phytopathology. 79: 395-401. 6. Gabler, F.M., J.L. Smilanick, M. Mansour, D.W. Raming, and B.E. Mackey. 2003 Table II. PROGIBB 4% application rates for varying quantities of water per acre targeted gibb concentration (ppm) water PROGIBB Varietal Recommendation1 per acre 4% per acre (gal) (fluid ounces) 2.5 50 0.5 2.5 75 0.7 2.5 100 0.9 7.5 50 1.4 7.5 75 2.1 7.5 100 2.8 20.0 50 3.8 20.0 75 5.7 20.0 100 7.6 Sauvignon Blanc Barbera, Carignane, Chardonnay, Chenin Blanc, Colombard, Pinot Noir, Petite Sirah, Tempranillo, Zinfandel 1. Source: Pro-Gibb 4% label, Valent BioSciences Corp., 2011. 74 p racti c al w i ne ry & v i ne yard MAY 20 13 Grenache "Correlations of morphological, anatomical, and chemical features of grape berries with resistance to Botrytis cinerea." Phytopathology. 93: 1263-1273. 7. Galet, P. 2000 General Viticulture. Oneoplurimedia, Chateau de Chaintre, France. 8. Grant, R.S. "Effect of timing and rate of gibberellin acid application." Unpublished report submitted to California Department of Pesticide Regulation, Oct 24, 1991. 9. Gubler, W.D., J.J. Marois, A.M. Bledsoe, and L.J. Bettiga. 1987 "Control of bunch rot in grape with canopy management." Plant Disease. 71 (July): 599-601. 10.Hed, B., H.K., Ngugi, and J.W. Travis. 2009 "Relationship between cluster compactness and bunch rot in Vignoles grapes." Plant Disease. 93: 1195-1201. 11.Marois, J.J., A.M. Bledsoe, L.J. Bettiga. 1992 "Botritis bunch rot and Miscellaneous secondary invaders and sour rot." In Grape Pest Management. Flaherty, D.L.; L.P. Christensen, W.T. Lanini, J.J. Marois, P.A. Phillips, L.T. Wilson (Eds.). Univ. Calif. Div. Agric. Sci, Oakland. 12.Marois, J.J., J.K. Nelson, J.C. Morrison, L.S. Lile, and A.M. Bledsoe. 1986 "The influence of berry contact within grape clusters on the development of Botrytis cinerea and epicuticular wax." Am. J. of Enol. & Vit. 37: 293-296. 13.Mullins, M.G., R. Bouquet, and L.E. Williams. 1992 Biology of the Grapevine. Cambridge, Cambridge University Press. 14.Percival, D.C., J.A. Sullivan, and K.H. Fisher. 1993 "Effect of cluster exposure, berry contact and cultivar on cuticular membrane formation and occurrence of bunch rot (Botrytis cinerea Pers.: Fr. with three Vitis vinifera L. cultivars.)" Vitis. 32: 87-97. 15.Salisbury, F.B. and C.W. Ross. 1978 Plant Physiology, 2nd edition. Belmont, CA: Wadsworth Publishing Company. 16.Stapleton, J.J. and R.S. Grant. 1992 "Leaf removal for non-chemical control of the summer bunch rot complex of wine grapes in the San Joaquin Valley." Plant Disease. 76: 205-208. 17.Vail, M.E. and J.J. Marois. 1991 "Grape cluster architecture and the susceptibility of berries to Botrytis cinerea." Phytopathology 81: 188-191. 18.Valent BioSciences Corporation. 2011 ProGibb 4% Plant Growth Regulator Solution. Document 2011-PG4%-0001. 19.Weaver, R.J., A.N. Kasimatis, and S.B. McCune. 1962 "Studies with gibberellin on wine grapes to decrease bunch rot." Am. J. of Enol. & Vit.13: 78-82. 20.Wilcox, W. 2007 "Understanding and controlling Botrytis." Practical Winery & Vineyard Mar/Apr, pp. 30-38. 21.Winkler, A.J., J.A. Cook, W.M. Kliewer, and L.A. Lider. 1974 General Viticulture. Berkeley: University of California Press. 22.Wolf, T.K., A.B.A.M. Baudoin, and N. Martinez-Ochoa.1997 "Effect of floral debris removal from fruit clusters on botrytis bunch rot of Chardonnay grapes." Vitis 36: 27-33.