The effect of inoculum concentration and time of application of various bactericides on the control of fire blight (Erwinia amylovora) under artificial inoculation

The efficacy of various bactericides for the control of fire blight (Erwinia amylovora) in pear flowers was tested. Bactericides were applied preventively one day before, or curatively one or three days after artificial inoculation with pathogen concentrations of 104, 105 and 107 cfu ml-1. The results indicated that a) preventive sprays were more effective than curative sprays; b) the effectiveness of curative sprays decreased progressively from the first to the third day; c) the infection was proportional to inoculum concentration, both in the water–sprayed (control) and in the bactericide–sprayed flowers. There was also significant interaction between bactericide and inoculum concentration. Best results were achieved with streptomycine (Agrept) at 0.5 g and 1 g l-1 H2O; oxolinic acid (S–0208) 1.5 g l-1 H2O; and flumequine (Firestop) 2 ml l-1 H2O. Kasugamycin (Kasumin), phosetyl–Al (Aliette) and copper hydroxide (Kocide) were less effective