Studies thoroughly during 47 years on weed species in the Republic Moldova have done. It was established that in our country are over 500 species of weeds, of which the dominant crops are 10-20, their degree of hazard for agricultural crops being different. Some of the species (C. cyanus L.) at the low weeding level increased harvest of wheat and rye. Genus Centaurea comprehend 550 species, including 26 species spread in the Republic Moldova. For folk medicine, rarely scientific, different species of genus Centaurea have particular importance in this type (C. cyanus L., C. jacea L.). Generally, studies in chemistry on therapeutic action of the species are diverse and very fragmented. Deeply scientific studies are necessary in the future. From this standpoint, weeds should not be totally destroyed, but kept a low negative impact on crops (threshold (limit) of biological damage) protected and even cultivated for medicinal proposes..