Effects of Temperature and Photoperiod on the Phenological Development of Barnyardgrass

An understanding of the environmental variables influencing the phenological development of weeds is essential for simulation model development. Temperature and photoperiod are important variables governing the phenological development of weeds. Growth cabinet studies were conducted to characterize the phenological development of barnyardgrass [ Echinochloa crus‐galli (L.) Beauv.] in response to variations in temperature and photoperiod and to determine the duration of the juvenile phase and the effect of temperature and photoperiod on reproductive development. Barnyardgrass was adapted to a temperature range of 6.5 to 52°C. Phenological development of barnyardgrass was described in terms of thermal days (cumulative day degrees above a base temperature for leaf appearance, tiller appearance, and shoot elongation). For modeling purposes, three development phases of barnyardgrass at a constant temperature of 20°C were described: (i) a juvenile phase of 1.5 thermal days; (ii) a photoperiod‐sensitive inductive phase of 4.1 thermal days; and (iii) a photoperiod‐sensitive postinductive phase of 19.5 thermal days. Photoperiod sensitivity of barnyardgrass did not differ with stage of development when expressed as a rate. Interpretation of constant sensitivity to photoperiod will simplify simulation of weed phenology in mechanistic models.