critical period of weed control in corn (zea mays l.)

abstract the critical period of weed control (cpwc) is a period in the crop growth cycle during which weeds must be controlled to prevent yield losses. in order to determine the critical period of weed control (cpwc) of corn in hamedan, an experiment was conducted in 2007 at agricultural research station of bu-ali sina university of hamedan. the experiment was carried out as a randomized complete block design with three replications. the trial included twelve treatments consisted of six initial weed-free periods in which plots were kept free of weeds for 0, 15 , 25, 35, 45 and 55 days after crop emergence (dae), and then weeds were allowed to grow until harvest and six initial weed-infested periods in which, weeds were allowed to grow for 0, 15, 25, 35, 45 and 55 dae, after which the plots were kept free of weeds until harvest. each plat consisted of four rows (six meter per row) with a row spacing of 75 cm. . weed sampling carried out in first series of treatments at the end of growth season and in second series of treatments at the4 end of infested periods. the results showed that beginning of cpwc ranged from 124 to 204 gdd, at 5% and 10% ayl, which equates to 8 and 16 days after crop emergence (3 and 5 leaf), respectively. the end of the cpwc varied from 395 to 289 gdd, at 5% and 10% ayl, which equates to 31 and 24 days after crop emergence(10 and 7 leaf), respectively. total dry weight of weeds increased as the duration of weed infested period increased and it was decreased with increasing duration of the weed-free period. grain yield of corn increased with increasing duration of the weed-free period and decreased as the duration of weed infested period increased.