Effect of plant density on critical period of weed control in canola (Brassica napus L.)

In order to study the effect of plant density on critical period of weed control in canola (Brassica napus L.), hybrid cultivar of hyola 401, a factorial experiment was conducted using a randomized complete blocks design with three replications at Rice Research Institute of Iran (RRII) in Rasht during 2008-2009 growing season. The factors included plant density (80 and 57 plants m-2) and periods of weed management based on growth stages the crop. These periods included five levels of weed control until crop emergence, 2, 4, 8 leaf stages and emergence of flowering bud initiation and five levels of weed interference until the above mentioned growth stages. Two additional treatments including full-season weedy and weed free checks were also prepared. The critical period of weed control was determined with the use of 5 and 10% acceptable yield loss levels by non-linear regression method and fitting logistic and gompertz equations to relative yield data. The results showed that the critical period of weed control in a density of 80 plants m-2 was between emergence to flowering bud initiation and planting to flowering (31.5-108.4 and 13.5-139.4 days after planting) and In a density of 57 plants m-2 was also between emergence to flowering and planting to flowering (25.5-115 and 4-143 days after planting) considering 10 and 5% acceptable yield loss, respectively. Therefore, the critical period started earlier and was also longer in a density of 57 plants than the density of 80 plants m-2. Weeds in field due to fall product were divided into fall and spring categories. Fall weeds in order of importance (in terms of density) were Poa trivialis, Phalaris minor, Ranunculus bulbosus and Rumex crispus. Spring weeds also were Erigeron Canadensis and Lythrum salicaria. The results also showed that plant density, control and interference of weeds and their interactions had significant effects on number and dry weight of weeds. The highest weed dry weight and number were related to 57 plants m-2 on interference treatment to 8 leaf stages.