The study of weed flora dynamics in agricultural crops is a complex and never-ending process which requires the continuous inventory and monitoring of problem weeds that cause the greatest damages on crops, according to which the most effective fighting strategies are established. The mapping action was carried out in fields cultivated with winter wheat in crop rotation and in monoculture crop from Ilfov, Giurgiu and Constanta counties. Weed files have been drawn up for each fields and they have shown the density, participation and constancy of each weed species. The analysis of the data shows that the dominant species in the fields where the wheat was cultivated in crop rotation system were: Veronica hederifolia, Veronica persica and Setaria pumila in Giurgiu county, V. hederifolia and V. persica in Ilfov county, V. hederifolia Polygonum convolvulus in Constanta county. In monoculture system the number of weeds was higher and several species appeared, including weeds on the list of invasive species: Ambrosia artemisifolia and Coniza Canadensis. Regarding the distribution of weed species by botanical groups, the largest group was the one of the annual dicotyledonous and among the perennial dicotyledonous the most important species were Cirsium arvense and Convolvulus arvensis. From the group of annual monocotyledonous, the most important species were those of the genre Setaria and broad-leaved cockspur (Echinochloa crus-galli), species that invades all cultures in our country and is found in all areas and is also considered to be an invasive species. The dominant species in both crop rotation and monoculture system belong to the Veronica genre, exceeding an average density of 100 plants/m(2.)
