Critical Period of Weed Control in Maize
2008
Mohammadi, G.R. (Razi University, Kermanshah, Iran), E-mail: [email protected]
In order to determine the critical period of weed control in maize, field studies were carried out in 2005 and 2006 at the Agricultural Research Farm of Razi University, Kermanshah, west Iran. Twelve treatments consisted of six initial weed-free periods in which plots were kept free of weeds for 0, 15, 30, 45, 60 and 75 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, 30, 45, 60 and 75 DAE, after which the plots were kept free of weeds until harvest. Full season weedy condition led to 91.1% and 85.1% reductions in maize grain yield compared to weed-free treatment for all of the growing season in 2005 and 2006, respectively. The beginning of the critical period of weed control ranged from 3 to 19 DAE in 2005 and from 10 to 24 DAE in 2006 with respect to accepted percentage of yield loss (2.5 to 10%). These times were approximately coincided with the 1 to 4-leaf stage or 28.5 to 185.5 accumulated thermal units (ATU) in 2005 and with 3 to 7-leaf stage or 146 to 364.5 ATU in 2006. The end of the critical period for different accepted percentage of yield loss, varied from 65 to 75 DAE in 2005 (approximately 16-leaf to mid tasseling stages or 887.5 to 1070.5 ATU) and from 48 to 65 DAE in 2006 (approximately 14-leaf to early tasseling stages or 779 to 1002.5 ATU).
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