A model to evaluate the consequences of GM and non‐GM segregation scenarios on GM crop placement in the landscape and cross‐pollination risk management

Under European regulations, a product is labelled as GM (genetically modified) if more than 0.9% of one of its ingredients originates from GM material. During collection, crops from many fields are combined to fill a silo. To avoid the risk of mixing GM and non‐GM harvests, it is possible to dedicate a silo to a given crop or to define specific times for GM and non‐GM product delivery to silos. To evaluate these scenarios for the maize supply chain, we propose a combination of a model of farmers’ varietal choice (based on profit evaluation at the field level, taking into account transport costs as well as price and cost differences between GM and non‐GM products) and a spatially‐explicit gene flow model. Consequences of different segregation strategies for collection zone organization can therefore be compared while using the percentage of GM grain in non‐GM crops due to cross‐pollination. The ‘temporal’ strategy leads to a uniform area of GM or non‐GM maize, depending on the prices and the weather risks. The ‘spatial’ strategy leads to areas of either GM or non‐GM crops surrounding the corresponding collection silo. GM presence in non‐GM batches depends on the size of the non‐GM zone and on the prevailing wind. We show how divergent commercial strategies of grain merchants could have consequences on GM presence in non‐GM batches.