The article demonstrates the results of the molecular analysis of 'Candidatus Phytoplasma solani' presence in some weed species, possible reservoirs of infection. During the study, the optimal conditions for the determination of phytoplasma in weeds were selected. The research was carried out over three years. The presence of the pathogen 'Ca. P. solani' was found in the plants of Solanum nigrum and Convolvulus arvense. Also, as a result of the study, it was established that the method of isolation by boiling in alkaline solution is the most efficient and allows to obtain truthful results compared to other methods used.