INFLUENCE OF TEMPERATURE, PHOTOPERIOD, AND IRRADIANCE ON THE PHENOLOGICAL DEVELOPMENT OF COMMON RAGWEED (AMBROSIA-ARTEMISIIFOLIA)

Implementation of an integrated weed management system requires predic tion of the effect of weed competition on crop yield. Predicting outco mes of weed competition is complicated by genetic and environmental va riation across years, locations, and management. Mechanistic models ha ve the potential to account for this variability. Weed phenological de velopment is an essential component of such models. Growth cabinet: st udies were conducted to characterize common ragweed's phenological res ponse to temperature, photoperiod, and irradiance. Ragweed development occurred over a temperature range of 8.0 to 31.7 C, and this response to temperature was best characterized using a nonlinear funct ion. A maximum leaf appearance rate of 1.02 leaves d(-1) occurred at 31.7 C. Ragweed has a short juvenile phase, during which it was not sensitive to photoperiod. Following this juvenile phase, sensitivity to photoper iod was constant and continued until pistillate flowers were observed. Photoperiods of 14 h or less were optimal and resulted in maximum rat es of development. Irradiance level affected ragweed phenological deve lopment only when combined with the additional stress of low temperatu res. Data generated in this study can be used for the development of m echanistic weed competition models.