Herbicide resistance is a desired trait for sugar beet (Beta vulgaris L.) production because it is a low-competitor crop that requires careful weed management. However, gene flow to weed beet (also B. vulgaris) could jeopardize the weed control strategy by causing the emergence of resistant weed beets; it could also lead to further adaptation of weed beet as a troublesome weed for other crops by selecting more competitive plants. To evaluate the hazard that such a selection process represents, apart the herbicide resistance, we investigated the morphology and reproduction of progeny of weed beets having inherited a herbicide resistance gene. First-generation resistant weed beet exhibited traits likely counter-selected. But such crop traits rapidly disappeared with backcrossing to weedy relatives: no biologically relevant difference was noted between resistant and susceptible near-isogenic siblings in the various experiments. In the absence of resistance selection, our data indicate low chances for weed beet to evolve more competitive forms than present weed beet populations. However, they also suggest that there is no fitness cost limiting transgenes spread.