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Field studies were carried out in 1989-1995 and 2006-2012 on plantations of sugar beet (Beta vulgaris L. subsp. vulgaris). During this period, 542 phytosociological relevés were made using the Braun-Blanquet method. In total, 46 weed species were found. In 1989-1995, the occurrence of 36 segetal species was reported. The highest cover indices were determined for Chenopodium album and Amaranthus retroflexus. Galium aparine, Echinochloa crus-galli, and Elymus repens were the dominant species, as well. Analysis of the frequency of occurrence revealed one constant species (Chenopodium album), two frequent species (Amaranthus retro- flexus and Galium aparine), and two medium-frequent species (Echinochloa crusgalli and Matricaria maritima ssp. inodora). In 2006-2012, the occurrence of 40 weed species on the sugar beet plantations was recorded. The plantations were clearly dominated by Chenopodium album, accompanied by Polygonum persicaria and Polygonum lapathifolium ssp. lapathifolium. Other dominant species comprised Setaria viridis, Galinsoga parviflora, Brassica napus ssp. napus, and Fallopia convolvulus. The Chenopodium album was a constant component of the sugar beet plantations. In turn, no frequent species were observed and six medium-frequent species were found (Setaria viridis, Galinsoga parviflora, Brassica napus ssp. napus, Echinochloa crus-galli, Amaranthus retroflexus, and Capsella bursa-pastoris). Noteworthy, the presence of previously unreported species, e.g., Abutilon theophrasti, Hyoscyamus niger, or Artemisia vulgaris, was revealed. These species are rare components in sugar beet crops. A reverse phenomenon, i.e., the disappearance of some species such as Euphorbia helioscopia, Malva neglecta, Rumex acetosella, Sinapis arvensis, or Sisymbrium officinale, was also observed. [ABSTRACT FROM AUTHOR]