| Summary: | Knowledge of the germination pattern and seed longevity of <i>Echinochloa colona</i> under field conditions could play a crucial role in effective weed management. Germination patterns of four populations (B17/12, B17/13, B17/7, and B17/25) of <i>E. colona</i> collected from eastern Australia were studied under field conditions for two years. Each population had multiple cohorts, and peak germination occurred in December 2018. Population B17/12 had a lower dormancy level compared with other populations, as 87% of the seeds germinated in the first cohort. Regression analysis revealed that populations B17/12, B17/13, B17/7, and B17/25 required 2130, 3110, 4320, and 6040 cumulative growing degree days (GDD), respectively, for 80% germination. The last cohorts of each population (100% germination) were observed in February 2020. This suggests that the populations of <i>E. colona</i> had innate dormancy, and a proportion of seeds can germinate in the next season. For the seed persistence study, seed bags of three populations (B17/4, B17/26, and B17/35) were exhumed at different intervals at two locations (Gatton and St George) over 30 months to evaluate decay components. Averaged over locations, burial duration, and burial depth, populations behaved similarly for the seed decay component. After 30 months of seed placement at Gatton, viable seeds at 1, 5, and 15 cm burial depths were 8, 26, and 15%, respectively. However, during the same time period at St George, viable seeds at 1, 5, and 15 cm burial depths were 0, 4, and 3%, respectively. These results implied that <i>E. colona</i> seeds persisted for a longer period (>2 years) in the light-textured soil (Gatton), particularly at the 5 cm burial depth. After 30 months of seed placement at Gatton, seeds decayed faster at 1 cm compared with the 5 cm burial depth. The studies demonstrated that seed persistence and germination patterns of <i>E. colona</i> may vary with different soil and agro-climatic conditions. The results suggest that management strategies should be followed to enable early control of <i>E. colona</i> over a three year period and that restricting reinfestation of weed seeds through seed rains could lead to almost complete control of <i>E. colona</i> in the field.
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