Three species of potato cultivated with or without pencycuron, an active substance of a com. seed treatment agent, were tested in 2011-2013 to assess their resistance against diseases of potato tubers induced by Rhizoctonia solani fungus and Streptomyces scabiei bacterium. Efficiency of the product was detd. by a standardized visual assessment of size damaged area. A significant decrease in damage of tubers induced by fungi was obsd. No protecting effect against the bacterium was however found.