Information on weed flora composition in agricultural fields is of important value in weed management decisions. The rapeseed (Brassica napus L.) was introduced in the cultivations in west of Iran recently. Subsequently, some weeds such as Phelipanche aegyptiaca are becoming increasing problem. Therefore, the study was conducted to study weed flora and determine the relationship between weeds and climatic, soil and agronomic factors in rapeseed fields in Mehran and Dehloran counties of Ilam province in Iran during 2019-2020. The weeds survey was done in 83 randomly selected rapeseed fields from five areas. Weed abundance and coverage were determined based on the Braun-Blanquet scale. Canonical correspondence analysis (CCA) was used to analyze the relationships between weed species coverage data and regions, production area, altitude, last year crop, soil texture, mean yearly precipitation, total rain current year, total rain current month, mean yearly temperature, mean temperature current year, mean temperature current month and sources of irrigation water. Totally, 14 weed species were found including 78.6% dicot and 21.4% monocot species. In addition, 71% and 29% of the weeds were annual and perennial, respectively. Malva sylvestris showed the highest frequency (100 %) and mean coverage (2.05%). The most important variables affecting weed coverage based on direct gradient analysis CCA were the last year crop, mean temperature current month, mean yearly precipitation, regions, total rain current year, mean yearly temperature, altitude, mean temperature current year, and sources of irrigation water. The first axis of CCA showed the highest correlation with the last year crop, altitude and mean temperature current month and had a positive and consistent correlation with the distribution of a weed Phelipanche aegyptiaca. In the negative part of the first axis and the positive part of the second axis, mean yearly precipitation, total rain current month and mean yearly temperature had the greatest effect and had a positive correlation with the distribution of Sorghum halepense, Alhagi maurorum, Hordeum sp. and Portulaca oleracea. In the negative part of the first and second axes total rain current year, mean temperature current year, region and source of irrigation water had the greatest impact. Malva sylvestris and Gundelia tuornefortii were placed in this section. In overall, the results showed that there is a significant correlation between the relative cover of weeds in rapeseed fields and climatic, soil and agronomic factors. Thus the results can be used to adapt weed management strategies in the cultivation.
