Mainly because of the climate change an increased spreading of phytoplasma transferring insects and therefore of the phytoplasma itself is observed. Since these plant pathogens can cause enormous economic losses and no direct control is possible, the aim of this project is to find successful and
practical control strategies using the commercially important grapevine yellows Bois Noir and grapevine flavescene dorée as model diseases. It is known that after infection with phytoplasma an increase of
the flavonoid biosynthesis occurs as a defence mechanism. It should be evaluated if an additional modification of the flavonoid biosynthesis a reduction of phytoplasma titer or even complete cure of the plant can be obtained. This additional modification can be achieved with prohexadione-Ca (Regalis©) at different concentrations and/or different application intervals. Prohexadione-Ca is currently used for inducing fire blight resistance in pome fruit production. In the case that only very high concentrations of prohexadione-Ca are able to reduce phytoplasma titer where also phytotoxic affects could occur, derivatives of the modified plant flavonoids could be used directly for spray application to avoid this phytotoxicity. Results of this one-year project the induction of plant defence mechanisms enable a target-orientated, practical, immediate and holistic phytoplasma control strategy.