Effects of temperature and photoperiod on the phenological development of barnyardgrass

An understanding of the environmental variables influencing the phenologica l development of weeds is essential for simulation model development. Tempe rature and photoperiod are important variables governing the phenological d evelopment 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 det ermine the duration of the juvenile phase and the effect of temperature and photoperiod on reproductive development, Barnyardgrass was adapted to a te mperature range of 6.5 to 52 degreesC, Phenological development of barnyard grass was described in terms of thermal days (cumulative day degrees above a base temperature for leaf appearance, tiller appearance, and shoot elonga tion). For modeling purposes, three development phases of barnyardgrass at a constant temperature of 20 degreesC were described: (i) a juvenile phase of 1.5 thermal days; (ii) a photoperiod-sensitive inductive phase of 4.1 th ermal days; and (iii) a photoperiod-sensitive postinductive phase of 19.5 t hermal days. Photoperiod sensitivity of barnyardgrass did not differ with s tage of development when expressed as a rate, Interpretation of constant se nsitivity to photoperiod will simplify simulation of weed phenology in mech anistic models.