This research aims to estimate the base temperature (Tb) and field emergence of eight Echinochloa crus-galli populations. Seeds from E. crus-galli populations were collected from maize fields from Denmark, Latvia, Germany, Czech Republic, France, Italy, Greece and Spain during summer 2023, and sent to Lleida (Spain). For each population, 50 seeds were placed in Petri dish and incubated on filter paper with distilled water at constant temperatures of 5, 8, 11, 14, 17, 20, 23, and 26 ºC, with 12h:12h photoperiod; four replicates were used. The germination of the seeds was followed daily, and germinated seeds were removed. The cumulative germination was plotted against time, and a sigmoid logistic model was applied to estimate time to 50 % emergence (T50) at each constant temperature. The inverse of T50 was plotted against temperature and a linear regression was applied. The point where the regression line intercepts the x axis will be the Tb for each respective population. Additionally, 100 seeds per population were sown in November 2023 in the experimental fields of the University of Lleida with four replicates. A manual soil disturbance was done in late March, following the typical seedbed preparation for maize in the area; however, E. crus-galli emergence was first observed in February. Seedling emergence was monitored every three to four days from February to May 2024. The cumulative emergence was plotted against hydrothermal time (HTT), using the estimated Tb for each population, and considering -2.0 MPa as base water potential. The estimated Tb was within the range estimated in previous research, being lowest in France (7.5 ºC), followed by Italy and Greece (9.6 ºC), Germany (10.1 ºC), Czech Republic (10.5 ºC), Denmark (10.6 ºC) and Latvia (11.5 ºC). The estimated Tb for the Spanish population was unexpectedly high (15.9 ºC), likely due to low germination percentages, and requires further confirmation. Regarding field emergence, two population groups could be distinguished: those that emerged mainly during winter, before soil disturbance (Central and North European populations from Latvia, Czech Republic, Denmark and Germany), and those that emerged after soil disturbance (Italy, Spain and France). Regarding the Greek population, only 1% of emergence was observed before soil disturbance. The emergence of all populations could be described with Gompertz or Weibull sigmoid functions. The results show that most European populations have similar Tb values, around 10 ºC, but also highlighted the existence of at least two main groups according to their emergence behaviour.
