Critical period of weed competition in onion (Allium cepa L.).
The effects of 12 weeding treatments on yield reduction in onion were studied on sandy loam soil at Mymensingh during December 1984-April 1985. The treatments were weed-free up to 12, 24, 36, 48 and 68 days after transplanting (DAT) and up to harvest as well as no weeding up to the same DAT and harvest. The major weeds were Chenopodium album, Oldenlandia corymbosa, Bonnaya brachiata, Vicia hirsuta and V. sativa. Compared to the control treatment (weed-free up to harvest; bulb yield 7.73 t/ha), bulb yield reduction was least in the plot kept weed-free up to 60 DAT (7.53 t/ha). No weeding up to harvest resulted in a 70% reduction in yield. The results indicated that the critical stage of crop-weed competition in onion is between 36 and 48 DAT.