The present invention relates to the novel use of an isothiazolecarboxamide of the formula (I) (common name: Isotianil) for controlling "Candidatus" Liberibacter spp and/or "Candidatus" Phytoplasma spp, preferably, "Candidatus" Liberibacter solanacearum and/or "Candidatus" Phytoplasma americanum, more preferred "Candidatus" Liberibacter solanacearum, in plants of the Solanaceae family, preferably in potatoes.