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 (...)
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R. Kenneth Horst (1992) studied this question.