Improving environmental risk assessment of pesticides: mapping crop development as function of calendar date across the EU for use in the EU regulatory framework Establishing a link between BBCH crop growth stages, calendar dates and degree‐days for a set of selected crops in Europe

EU Regulation 1107/2009 requires environmental risk assessments (ERA) for non-target organisms exposed to active substances in plant protection products. To advance the ERA of pesticides effectively, it is important to consider and assess the relationship between crop development stages (BBCH), calendar dates and locations across the EU. Therefore, the present study aims to enhance pesticide risk assessment for non-target organisms by precisely mapping crop development stages (BBCH) across the EU. This involved extensive data collection and curation from sources like C2D2, PEP725, and TEMPO, alongside literature, creating a harmonized database of over 1.2 million phenological observations. Rigorous cleaning processes addressed inconsistencies and duplicates across these diverse datasets. Comparisons revealed C2D2's broad spatial coverage across Europe, while PEP725 concentrated in Central Europe and TEMPO in France. C2D2 and TEMPO offered observations across various growth stages, unlike PEP725 which focused on sowing, emergence, and harvest. While C2D2 and PEP725 generally aligned for cereals and sunflower, harvest dates sometimes differed significantly. Similarly, C2D2 and TEMPO showed slight variations for maize and sunflower. To address data gaps and spatial variability, the study developed models for predicting sowing dates and phenological stages. Sowing dates were predicted using a temperature-driven rule, supplemented by a median rule for regions where management practices (like irrigation) heavily influence planting, as seen with maize in Southern Europe. The WOFOST cropping system model's phenological sub-model was used to predict development stages, accounting for temperature, photoperiod, and vernalization. Calibration of WOFOST showed better results for winter crops compared to the spring crops. In conclusion, the project successfully established a comprehensive phenology database and robust modeling framework. This provides valuable, precise spatio-temporal information on crop development, significantly improving environmental risk assessment for pesticides in the EU regulatory context. Future efforts could focus on aggregated crop groups to further improve model calibration and reduce extrapolation needs.