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Reduction of Powdery Mildew and Other Diseases by Over-the-Trellis Applications of Lime Sulfur to Dormant Grapevines. DAVID M. GADOURY, Senior Research Associate, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. ROGER C. PEARSON, Professor, DUANE G. RIEGEL, Technician, ROBERT C. SEEM, Associate Professor, and CHRISTOPHER M. BECKER, Research Associate, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456, and JAY W. PSCHEIDT, Assistant Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Plant Dis. 78:83-87. Accepted for publication 3 September 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0083.

From 72 to 96% of the ascospores within cleistothecia of Uncinula necator were killed in the spring when exposed to lime sulfur (calcium polysulfide), copper sulfate, copper hydroxide, or copper oxychloride for 5 min in laboratory assays. Dinocap reduced viability in the same assay when the exposure time was more than 1 hr. Neither sulfur nor triadimefon significantly reduced viability. Cleistothecia collected in fall were not affected by the above fungicidal compounds in a 5-min exposure. One hour of exposure to lime sulfur or 8 hr of exposure to copper sulfate was required before ascospore viability was significantly reduced in the fall. Aqueous solutions of lime sulfur at a concentration of 120 ml/L, applied as over-the-trellis sprays at 2,800 L/ ha (336 L/ ha of lime sulfur) to dormant grapevines in spring, killed cleistothecia of Uncinula necator on the bark of the vines and delayed the development of epidemics of powdery mildew. A lower rate of application was not effective against powdery mildew. The delay of the epidemic ranged from a few days to several weeks, depending upon the rate of toxicant used, the resistance of the host to powdery mildew, and the favorability of environmental conditions for disease development. In vineyard trials, the severity of fruit infection was reduced from 43.1 to 14.1% in 1986, from 4.6 to 0.1% in 1988, and from 41.4 to 27.2% in 1989 by a single eradicant treatment of lime sulfur to the Vitis interspecific hybrid cultivar Rosette, which is highly susceptible to powdery mildew. The same rate of lime sulfur reduced the severity of powdery mildew from 30.8 to 0.3% in 1988 on the more resistant cultivar Vilis labruscana 'Concord'. The incidence of angular leaf scorch (Pseudopezicula tetraspora) and Phomopsis cane and leaf spot (Phomopsis viticola) was also decreased by over-the-trellis applications of an aqueous solution of lime sulfur at a concentration of 40 ml/L and 120 ml/L. The incidence and severity of black rot of grapes (Guignardia bidwellii) was reduced by 120 ml/L of lime sulfur in 1991, but not in 1992.

Keyword(s): Oidium, eradication, sanitation