Downey mildew, powdery mildew and black spot in the agroecological production of roses

Abstract

The rosebush is a crop with high nutritional requirements, requiring frequent replacement of fertilizers, which can lead to soil salinity. The agroecological farming is an alternative to prevent the environmental impacts provided by the overuse of fertilizers and pesticides. The objective was to assess the incidence and severity of downey mildew, powdery mildew and black spot in cultivars of roses and observe which one would have better adjustment to agroecological farming system. The experiment was conducted at EPAMIG in São João del-Rei, MG, in open fields, in two production systems: agroecological and conventional. The experimental design was randomized blocks with six treatments corresponding to the agroecological farming of six cultivars of roses plus two additional treatments corresponding to the conventional cultivation of two cultivars of rose, totaling eight treatments (6+2) with four repetitions giving 32 experimental plots. Agroecosystem were tested in six cultivars of roses, which are: Hollywood, Capri, Carola, Grand Gala, Greta and Vegas. In the conventional system were tested cultivars Carola and Vegas. Agroecosystem production management used only authorized/registered products for organic agriculture and production techniques inherent in this system. Green manures Canavalia ensiformis and Arachis pintoi were planted between the lines and bed edges and fertilization was performed with biofertilizers. Weekly samples were taken assess incidence and severity of downy mildew, powdery mildew and black spot. Incidence was determined by the presence or absence of leaves with lesions in the experimental unit. Severity was obtained with aid of diagrammatic scales. Percentages of severity and incidence were transformed into areas under the curve of progress of severity (AUCPS) and of incidence (AUCPI). It was observed that the cultivars Capri, Hollywood and Vegas in agroecological farming were more susceptible to black spot due to higher AUCPS values than the other cultivars in both agroecosystem and conventional system. For downy mildew severity cultivars Capri, Grand Gala, Greta and Vegas in agroecosystem and Vegas in conventional system had bigger AUCPS values and higher incidence was observed in cultivars Greta and Vegas in agroecosystem. For powdery mildew cultivars Carola and Vegas in conventional system had higher AUCPS values. In agroecosystem no powdery mildew was observed. Production of these rose cultivars in the agroecosystem is not feasible due to their vulnerability to most diseases evaluated in this study.