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Effect of Sodium Bicarbonate and Oils on the Control of Powdery Mildew and Black Spot of Roses. R. K. Horst, Professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. S. O. Kawamoto, and L. L. Porter. Research Support Specialist, and Research Assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. 76:247-251. Accepted for publication 23 August 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0247.

Powdery mildew, caused by Sphaerotheca pannosa var. rosae, and black spot, caused by Diplocarpon rosae, were significantly controlled by weekly sprays of 0.063 M aqueous solution of sodium bicarbonate plus 1.0% (v/v) Sunspray ultrafine spray oil on Rosa spp. Control of powdery mildew was evaluated on cultivars Bridal Pink, Gold Rush, Lavande, Prive, Samantha, Sonia, and Royalty in greenhouse experiments, and control of black spot was evaluated on cultivars Mr. Lincoln and Pascale in field experiments. The chemicals were eradicative when applied individually or in combination; however, for powdery mildew control, treatment in combination was better (P = 0.0002). These results indicate that sodium bicarbonate and oil appear to be effective biocompatible fungicides for control of powdery mildew and black spot of roses. Differences in response to powdery mildew among the cultivars ranged from complete resistance in Gold Rush to high susceptibility in Samantha.