Powdery mildew (Podosphaera pannosa) is a major disease of roses which reduces yield and quality through growth of mycelia on different parts of the rose plant which affects their salability. The disease is wide spread where roses are grown both in greenhouse and field. This study was carried out to evaluate the effects of Bacillus spp and sodium nitrophenolate on powdery mildew of roses in greenhouse conditions. The trial was done in an already established bush of roses in the greenhouses at Kikuyu in Kiambu County and at Naivasha in Nakuru County both are in Kenya. The experiment was conducted on a variety known as A one which is grown in different farms in Kenya. Weekly foliar application of Real subtilis® (Bacillus subtilis) at the rate of 2ml/L, Hatake (Bacillus amyloliquefaciens) 3.0g/L, Atonik® (sodium nitrophenolate) 1ml/L and Meltatox® (Dodemorph acetate) 2.5ml/L. In the second experiment, foliar application of Bacillus amyloliquefaciens was done at different concentrations and at various intervals of application as follows 1.5g/L, 4 days, 3.0g/L, 4 days, 4.5g/L 4 days, 1.5g/L, 7 days, 3.0g/L, 7 days, 4.5g/L, 7 days, 1.5g/L, 10 days, 3.0g/L, 10 days, 4.5g/L, 10 days and no treatment as control. The experiment was laid out in a randomized complete block design with four replications for each treatment in plots with 44 plants. Data was collected on incidence and severity of powdery mildew on weekly basis while data on stem length, bud diameter, bud length and marketable grade were collected daily for twenty weeks and six weeks for the first and the second experiments respectively. In the first experiment, Bacillus subtilis, B. amyloliquefaciens, sodium nitrophenolate and dodemorph acetate significantly reduced incidence of powdery mildew from 83% to 55% with dodemorph acetate posting the best results followed by B. amyloliquefaciens, sodium nitrophenolate and Bacillus subtilis. In the second experiment, at different rates and at various intervals Bacillus amyloliquefaciens reduced incidence of powdery mildew with the rate of 1.5g/L at four and seven day intervals gave better results than ten days interval. Disease severity was reduced significantly from 15.8% to 2.1% by application of dodemorph acetate and B. amyloliquefaciens while application of B. subtilis and sodium nitrophenolate did not significantly at P ≤0.05 reduce severity of powdery mildew. Applications at the rate of 1.5g/L and 3.0g/L at four days and weekly applications had the highest reduction in severity in the second experiment. Dodemorph acetate had the highest area under disease progress curve (932) followed by Bacillus amyloliquefaciens (988) in the first experiment while application of Bacillus amyloliquefaciens at the rate of 1.5g/L at the interval of seven days showed the highest AUDPC (799.8). Application of the test products did not significantly affect the yield and quality paramenters in the first experiment but in the second experiment, foliar application of Bacillus amyloloquefaciens at different rates and at various intervals improved the quality. Marketable stems significantly increased in the second experiment after the application of Bacillus amyloliquefaciens at different rates and at various intervals. Foliar application of Bacillus Spp and sodium nitrophenolate controlled powdery mildew of roses. Application of the same products did not have significant effects on quality and yield parameters of flowers such as flower bud length, stem length and bud diameter and number of stems produced in the first experiment, however, there was improvement in yield and quality in the second experiment. Growers of roses should be encouraged to apply Bacillus spp and sodium nitrophenolate in managing powdery mildew. The optimal concentration of Bacillus amyloliquefaciens should be established and how sodium nitrophenolate induce resistance to plants against phytopathogens should be investigated.

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