Effects of photoperiod on the phenological development of redroot pigweed (Amaranthus retroflexus L.)

Mechanistic weed models focus on determining the outcome of weed and crop i nterference. An understanding of weed phenology is essential far simulation model development. Phenological development is a major factor determining the outcome of weed-crop competition. Growth cabinet studies were conducted to characterize the influence of photoperiod on the phenological developme nt of redroot pigweed (Amaranthus retroflexus L.). Results indicated that r edroot pigweed is a quantitative short-day species. Four development phases of redroot pigweed were described according to its response to photoperiod : (1) a juvenile phase of 1.1 d; (2) a photoperied-sensitive inductive phas e of 7.9 d; (3) a photoperiod-sensitive post-inductive phase of 39.9 d; and (4) a photoperiod-insensitive phase of 2.2 d. This information is useful f or the development of mechanistic models and for comprehending the distribu tion and competitive ability of redroot pigweed with crops. The utilization of these results could help in predicting the phenological development of redroot pigweed.