A field experiment using a randomized complete block design with three replications was conducted during the 2017 cropping year to determine (i) the critical periods of crop-weed competitions in roselle production and (ii) effects of weed competition periods on roselle growth and yield performance. The experiment consisted of 14 treatments in two series, including increasing duration of weedy periods (IDWP) and increasing duration of weed-free periods (IDWFP), which were compared with a weedy check (WC) and weed-free check (WFC). Weeds were permitted to compete with the roselle for 15, 30, 45, 60, 75, and 90 days after transplanting (DAT), and throughout the growing periods along with a WFC. Weed density and dry biomass increased, whereas crop parameters were decreased in IDWP. The reverse was true in IDWFP both for weed and crop parameters considered. The highest fresh and dried calyx yields were obtained from WFC, followed by 90 DAT in IDWFP; while the lowest was from WC, followed by 75 and 90 DAT in IDWP. Overall, to reduce the yield loss by more than 5% and realize a higher economic return, weeds must be kept free within 20 to 75 DAT as this is a critical period of weed-crop competitions.

Keywords: Critical period, dried calyxes, fresh calyxes, IDWFP, IDWP, roselle