Biorational treatments to manage dryberry of blackberry caused by Peronospora sparsa

Abstract

Downy mildew caused by Peronospora sparsa Berk is one of the most important diseases of blackberry in Mexico, causing losses of up to 70%. Although disease management programs have been previously evaluated, no information on the effect of biological and biorational compounds is currently available. The objectives of this study were to evaluate the pathogenicity of P. sparsa on the cultivars Tupi and Kiowa and to evaluate the effect of biological fungicides, sanitizing agents, potassium phosphite and plant resistance inducers. The experiments were conducted in commercial fields in 2009, 2010 and 2012 in Los Reyes and Ziracuaretiro municipalities in Michoacán State, Mexico, from bud brake to fruit ripening. Commercial formulations of Bacillus subtilis, citrus seed extract, copper sulfate, glutathione-oligosaccharins, harpin protein, hydrogen peroxide, potassium phosphite, and Trichoderma harzianum were sprayed every 10–14 days. Pathogenicity tests confirmed infection in the Tupi and Kiowa cultivars producing the typical symptoms on leaflets at 12 and 16 days after inoculation, respectively. There were significant differences between the treatments (P < 0.001). The incidence of dryberry in the controls was 27, 24, and 18% in 2009, 2010 and 2012, respectively. The treatments that were based on potassium phosphite and glutathione-oligosaccharins resulted in the lowest incidence (0.66–13%) compared to that of the control in the 3 years of testing. B. subtilis, T. harzianum, copper sulfate, citrus seed extract and hydroxide peroxide provided the lowest level of control (15–19% incidence) compared to that of the control.