Beets are a crop of particular concern regarding invasiveness questions because they commonly become feral due to unintentional hybridization with annual forms of wild beets. In this study the performance of transgenic beets resistant to Beet Necrotic Yellow Vein Virus (BNYVV) was compared to the performance of unmodified material from the same breeding line. Both transgenic and control genotypes were also compared to a conventionally bred variety carrying a similar phenotypic trait. Field tests were developed in a step by step fashion in order to study seed emergence and competitiveness in early life stages. The tests quantified the potential ecological advantage of virus resistance under virus and non-virus infestation conditions. In experimental field releases in 1993 and 1994 in Germany, a small but increasingly clear ‘additive’ ecological advantage of the genetically engineered trait was detected. In both years and all competition treatments, the conventional tolerant variety performed best. An impact of naturalization on natural, non-agricultural habitats may appear in wild beet populations in Italian seed beet production areas. However, a survey of coastal areas of North-Eastern Italy found no virus infestation in 1994, suggesting that an increase in wild beet fitness is unlikely to occur.