Reduction in ooze formation on fruit trees after repeated fosetyl-Al treatmentsin the control of fire blight

Abstract: Recently, different molecules have been developed for fire blight control with the aimto induce plant defense reactions on the fruit trees before a fire blight infection occurs. InBelgium Vacciplant, a compound on the base of laminarin has been registered for this purposewhile in other European countries fosetyl-Al has been registered since many years. Thesemolecules have no bactericide properties as such, but can change the host susceptibility for fireblight infections. These plant defense enhancing (PDE) molecules should be applied preventivelybefore fire blight infections occur: for blossom protection this means that the treatments shouldbe placed between the green bud and begin bloom stages. In an earlier publication it was shownthat the susceptibility of immature fruits to fire blight infections can be influenced by repeatedtreatments of fosetyl-Al applied on the trees as a plant defense inducing molecule. In recent trialson apple and pear, we have seen a substantial reduction in infected area and in bacterial oozeformation on the immature fruits when the trees were preventively treated with fosetyl-Al(Deckers et al., 2011). This reduction in ooze production of the fruits is considered to be a veryinteresting factor in the fire blight epidemiology, because it can help to reduce the increase inbacterial inoculum in the orchard like it usually occurs after trauma blight under natural infectioncondition. Recent trials have been done on apple and pear to see if this reduction in oozeformation after repeated plant defense inducing treatments was also possible on other organs, likeshoots and blossoms. The results of these trials will be discussed in this paper. Finally, theinduction of an abiotic stress in fruit trees by repeated treatments of heavy metals like Cu and Mncan result in an induction of a plant defense reaction and could be helpful in a fire blight controlstrategy under orchard conditions.