Population-based threshold models describe weed germination and emergence patterns across varying temperature, moisture and oxygen conditions.
Opportunities for diversifying the management of weedy populations may be enhanced through accurate predictions of seedling emergence, because the timing and success of control measures often hinges on the timing of weed emergence. We used population-based threshold models to establish the temperature, moisture and oxygen conditions for optimum germination of herbicide-resistant and -susceptible Echinochloa phyllopogon, a weed of temperate paddy rice, and applied them to predict emergence from field soil. We combined hydrothermal time for germination, accounting for within-population variation in base water potentials (Ψb), with thermal time for early seedling growth to predict the quantity and proportional size of the emergence flushes that constitute final recruitment. Emergence in field soils was reduced by moisture stress and flooding, especially for the resistant population. In all populations, germination rates increased between 9.5 and 31°C, Ψb was <-1.0 MPa, and there was no sensitivity to oxygen supply. Synthesis and applications. Population-based threshold models produced physiologically meaningful germination parameters, which are useful in defining the environmental constraints to germination, and predicting Echinochloa phyllopogon germination and emergence in field soils. By exploring the effects of temperature, water stress and flooding on germination and emergence, we predict irrigation regimes for optimising recruitment and the timing of weed control.