Effects of temperature and photoperiod on Setaria viridis

Understanding the environmental variables influencing the phenological deve lopment of weeds is essential for simulation model development. Temperature and photoperiod are important variables governing the phenological develop ment of weeds. Growth cabinet studies were conducted to characterize the ph enological development of Setaria viridis in response to variations in temp erature and photoperiod and to determine the duration of the juvenile phase and the effect of temperature and photoperiod on reproductive development Setaria viridis was adapted to a temperature range from 6.5 to 47 C. Phenol ogical development of S. viridis was described accurately in terms of therm al days (cumulative day degrees above a base temperature) and biological da ys (Bd: chronological days at the optimum temperature and photoperiod). Fou r developmental phases of S. viridis were described: (1) a juvenile (photop eriod insensitive) phase of 2.6 Ed; (2) a photoperiod-sensitive inductive p hase of 2.2 Ed; (3) a photoperiod-sensitive postinductive phase of 6.0 Ed; and (4) a photoperiod-insensitive inductive phase of 10.9 Ed. Photoperiod s ensitivity of S. viridis did not differ with stage of development when expr essed as a rate. interpretation of constant sensitivity to photoperiod will simplify simulation of weed phenology in mechanistic models.