crop rotation effects on the critical period of weed control in canola

background and objectives. integrated weed management approaches can help to decline costs weed control and improve its condition. critical period of weed control (cpwc) is defined as the best time for weeding. if cpwc is recognized we can accurately use herbicides and prevent environmental pollutions. beginning and duration of cpwc despond on some agents such as crop and weed traits, environment and agronomical factors. with respect to inexistence data about the effect crop rotation on the cpwc this study was done. materials and methods. in order to determine effect two different crop rotations (wheat – canola and soybean-canola) on the critical period of weed control in rape seed, two experimental designs were performed for the first and second rotation in 2011 and 2012, respectively. these studies did in the suburban of galugah region in randomize completely block format with three replications. treatments included periods of weed management on the canola growth stages(five weeding and competition levels up emergence , two leaf stage , four leaf stage , eight leaf stage , flowering stage plus two control treatments). results. findings showed canarygrass dominated in both rotations. species diversity in soybean-canola rotation by using shannon index (h= 0.69) was higher than wheat-canola (h= 0.45) .canola yield was 4060 and 2280 kg ha-1 in the wheat-canola and soybean-canola rotations, respectively. further yield in the first rotation can be related to positive role of organic matter which was more in the soil and its influence on the most important yield component that was number pod in each plant. the cpwc for wheat- canola rotation was between 161 and 354 days after planting(dap) (emergence to six-leaf stage) and between 65 to 920 dap(planting up maturity stage), using 5 percent acceptable yield reduction. conclusion. cpwc in soybean-canola rotation relative to wheat-canola rotation begined sooner and its duration also was longer. background and objectives. integrated weed management approaches can help to decline costs weed control and improve its condition. critical period of weed control (cpwc) is defined as the best time for weeding. if cpwc is recognized we can accurately use herbicides and prevent environmental pollutions. beginning and duration of cpwc despond on some agents such as crop and weed traits, environment and agronomical factors. with respect to inexistence data about the effect crop rotation on the cpwc this study was done. materials and methods. in order to determine effect two different crop rotations (wheat – canola and soybean-canola) on the critical period of weed control in rape seed, two experimental designs were performed for the first and second rotation in 2011 and 2012, respectively. these studies did in the suburban of galugah region in randomize completely block format with three replications. treatments included periods of weed management on the canola growth stages(five weeding and competition levels up emergence , two leaf stage , four leaf stage , eight leaf stage , flowering stage plus two control treatments).