Effect of bactericides, phosphonates and nutrient amendments on blast of dormant flower buds of pear: a field evaluation for disease control

Blast of dormant flower buds (BDFB) of pear is a disease of economic importance in the major pear production areas of Europe. To obtain information concerning control measures and disease origin, chemical control trials were performed which included bactericides (kasugamycin and copper), phosphonates (fosetyl–Al and ethephon), and nutrient amendments (boron, calcium, and microelements). Although Cu levels in bactericidal treatments and microelements in nutrient amendments increased significantly in trees, there was no significant effect on disease control. However, incidence of disease was reduced significantly with phosphonate derivative compounds, and effects were observed only the year after the treatment was performed. Additional field trials were done to determine optimum dose and application timing, and a schedule consisting of three spray applications of fosetyl–Al (240 g a.i. hl^-1) during May and June was the most effective treatment. This schedule was evaluated in 31 field trials performed in commercial orchard plots from 1989 through 1998. In the year after the treatment, average disease incidence decreased in 30 of 31 trials. The decrease of disease incidence was significant in 71% of the trials (average decrease of 46%). Neither the presence nor the population levels of P. syringae were consistently related to disease levels nor to the fosetyl–Al treatment effects on blast incidence of dormant flower buds.