Gene flow via seed or pollen is a basic biological principle of plant evolution. The genetic and ecological consequences of gene flow depend on the amount and direction of gene flow as well as on the fitness of hybrids. In Europe, wild relatives of cultivated beet are important plant genetic resources; the conservation of wild beet diversity has become an important task inbiosafety research. We have recently shown that a century of gene flow from Beta vulgaris ssp. vulgaris has not altered the genetic diversity of wild Beta vulgaris ssp. maritima in the Italian sugar beet seed production area. The assessment of potential risks of transgenic plants also has to take into account that conventional crops cross with wild plants. Unintended products of these crosses are weed beets that bolt and flower during their first year of planting. Weed beets cause harvest delays and yield losses. Gene flow is hard to control in wind-pollinated plants. At the same time, wild and weed beet populations undergo evolutionary changes and may expand their geographical distribution areas. The precautionary approach to risk management necessitates monitoring the local wild and weed populations that might be affected by transgene escape. Here, we present the methodology used for monitoring the geographical distribution and diversity of Beta populations in California and Italy. Future research should focus on the evolution of wild beet populations in comparison to baseline data. Two monitoring models are presented showing how endpoints can be measured: 1) 'Prior-After' crop commercialization against today's baseline and 2) 'Parallel' to crop commercialization against GMO-free reference areas/populations. Model 2 has the advantage of taking dynamic changes into account. Model 1 is superior if gene flow is so strong that unaffected areas/populations will not be found. Any assessment should be carried out realistically in comparison to natural variation of plant population parameters.