The article presents data that reveal the phases of dithylenchosis in potato tubers infested by the nematode Ditylenchus destructor, the density of parasitic nematodes, saprophytic and the type of popular in the infested plant tissue. It has been established that in the potato tubers infested in phases 1 and 2 of dithylenchosis, the monotypic primary populate of tubers with this parasite takes place. By density are distinguished: larval forms (L2, L3, L4 -50% of the total units / gram of infested tissue), eggs (17.45%), males (16.83%) and females (15.72%). In these phases of dithylenchosis, infested tubers are the main source of the nematode D.destructor spread in Solanaceae crops, because the external symptoms are not visible even by careful selection.