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 import ance in the major pear production areas of Europe. To obtain information co ncerning control measures and disease origin, chemical control trials were performed which included bactericides (kasugamycin and copper), phosphonate s (fosetyl-Al and ethephon), and nutrient amendments (boron, calcium, and m icroelements). Although Cu levels in bactericidal treatments and microeleme nts in nutrient amendments increased significantly in trees, there was no s ignificant effect on disease control. However, incidence of disease was red uced 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 sc hedule 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 wa s evaluated in 31 field trials performed in commercial orchard plots from 1 989 through 1998. In the year after the treatment, average disease incidenc e decreased in 30 of 31 trials. The decrease of disease incidence was signi ficant in 71% of the trials (average decrease of 46%). Neither the presence nor the population levels of P. syringae were consistently related to dise ase levels nor to the fosetyl-Al treatment effects on blast incidence of do rmant flower buds.