Assessment and management of risks associated to transgenic crops cultivation require a quantification of the various processes involved in the spread and persistence of transgenes outside of cultivated fields. Oilseed rape (Brassica napus L. ssp oleifera) is a 'sensitive' crop since it can cross, more or less easily, with wild relatives and can colonise natural or semi-natural habitats in the vicinity of the cultivated fields. The persistence of feral plants outside of fields is an important component of risk assessment and management since feral populations could be reservoir and/or corridors for genetic pollution between GM and GM-free productions. At the scale of an agricultural landscape, we performed a study (collaborating with CETIOM and INRA) to determine spatial distribution and dynamics of feral populations. This study shows (i) that relict plants of now unmarketable cultivars persist at least 8 years after their last cultivation (likely in the seed-bank), (ii) that feral populations persist also by local recruitment and (iii) that the spatial distribution of feral populations is partially related with carrying traffic of harvests from fields towards the silo.