Critical period of weed control in three winter oilseed rape (Brassica napus L.) cultivars

摘要

Field experiments were conducted in Tabriz, Iran, during 2004-05 and 2005-06 on winter oilseed rape cultivars Okapi, Licord, and SLM046 with 12 weed interference durations. The experiments consisted of 2 sets of treatments. In the first set, the crop was kept weed-free until the growth stages of 4-leaf, 8-leaf, stem elongation, flowering, and podding. In the second set, weeds were permitted to grow within the crop until the above mentioned growth stages. Weedy and weed-free controls were also included in the study. Different weed interference durations and cultivar x year interaction affected significantly the grain, oil, and biological yield, but not the percentage of oil. The minimum values of these traits were observed under the full weed-infestation condition. Maximum values for grain yield, oil and biological yield belonged to the weed-free control and SLM046 in both years. Regression models showed that to prevent >10% grain and oil yield loss, rape must be kept weed-free between the 6-leaf stage and initial flowering (47-110 days after emergence) and for biological yield between the 7-leaf stage and stem elongation (52-94 days after emergence)..