Phytoplasmas in pome fruit trees: update of their presence in Belgium and of the control of their vector.

Among the numerous diseases that can attack pome fruit trees, apple proliferation and pear decline, both caused by a phytoplasma (Candidatus Phytoplasma mali (AP) and Ca. P. pyri (PD), respectively) may cause important losses of quality and quantity of the crop. Until a few years ago no scientific and
reliable data on their presence in Belgium were available and so a survey was organised during 2 years to obtain more detailed information on the status of both pathogens. Root and leaf samples collected in commercial orchards were analysed using molecular detection tools and strains were identified. Additionally, the importance of PD vectors in pear orchards was assessed during the project.
In pear growing, the most abundant pest is an infestation with the psyllid Cacopsylla pyri, one of the vectors of pear decline. Simultaneous observations of its population dynamics, migration pattern and infectivity provided us with useful details of the risk of spreading the disease under Belgian climatological and cultivation conditions. Due to its fast and overlapping stadia during the same season it is often difficult to keep the infestation low or to eliminate it entirely. Based upon efficacy results of several plant protection products (integrated and biological) that were tested in field trials, spraying schedules were developed to control pear psyllids and preventing the spread of Ca. P. pyri by its vector.
Finally, the obtained status information on apple proliferation phytoplasma and pear decline is compiled in a report following the ISPM8 guidelines and transmitted to the federal authorities, together with the vector transmission risk information which was gathered. The report will contribute to a more extensive risk assessment and potential review of the regulation status of these pathogens in Belgium and the EU.