Cultivar resistance and chemical, biological and fertilizer treatments for controling Botrytis leaf blight of onion

Abstract

Botrytis leaf blight, caused by Botrytis squamosa, is an important disease of onion, mainly in the Southern region of Brazil. Studies on disease management that include host resistance, chemical, biological and alternative methods are scarce in the region. This work aimed to evaluate the effect of control treatments and 40 onion genotypes with varying resistance levels on disease management. Control treatments included seven fungicides, one biocontrol agent, and a calcium phosphite treatment. Among the genotypes, Ônix and Libório cv. exhibited the lowest levels of disease severity in the 2015 experiment, while the Bola Agroecológica, Preciosa, Ônix, and Super Agroecológica cv. were least affected in the 2016 experiment. Trifloxistrobin (75 g/ha) + tebuconazole (150 g/ha); boscalid (200 g/ha) + kresoxim-methyl (100 g/ha); and fluazinam (398.4 g/ha) best controlled the disease, while dicarboximides, Bacillus subtilis and phosphorus pentoxide (600 g/ha) + calcium (120 g/ha) did not differ from the control. We updated the data on host resistance to Botrytis squamosa and report for the first time the inefficacy of iprodione and procymidone for controlling Botrytis leaf blight in Brazil.