RELATIVE EFFECT OF WEEDS ON TOPPING AND RATOONING RAPESEED (BRASSICA-NAPUS L)

Experiments were conducted with Westar rapeseed (Brassica napus L.) to determine the effect of weeds at different growth stages on topping dry matter and seed yield of ratooned crop. Dry matter yield of weed-free plots was greater than that of weedy plot; this was most pronounced with topping at the bud stage and at first flower. At the earlier topping stages, the crop dry matter was more than that of the oats, indicating greater early season growth of the rapeseed than of the oats. Early topping between pre-bud and bud stage allowed competition from the weeds for the longest period of time and resulted in the lowest seed yield and highest weed dry matter as compared to crop topped late at first flower (3/4 plant cut) or removal of secondary branches, even lowest in the check plots (un-topped). The removal of secondary branches produced highest seed yield overall treatments including check plots under both weedy and weed-free conditions but was worst for topping dry matter.