Critical Period of Weed Control in Dragon's head (Lallemantia iberica Fisch. et Mey)

To determine the critical period of weed control in Dragon’s head (Lallemantia iberica Fisch. et Mey)، field study were conducted in 2011 at the Agricultural Research station of University of Tabriz. Experiment were conducted in randomized complete block design with 3 replications and treatments relevant included 13، 23، 33، 43، 53 and 63 days weeding during the growing season (free of weeds)، and 13، 23، 33، 43، 53 and 63 days without weeding (weed infested) in the growing season and includes free of weed، weed infested in the entire growing season and pure weed treatments in each block. The prevalent weed species were Setaria viridis L.، Chenopodium album L.، Acroptilon repense L.، Cichurium intybus L.، Amaranthus retroflexus L.، Xanthium strumarium L.، Anchusa italica Retz.، Convolvulus arvensis L. and Salsola kali L. respectively. These species constituted 23، 18، 15، 15، 9، 7، 6، 3 and 2% of total weed population، respectively. Analysis of variance results showed that weed dry weight with increasing duration of infection and reduce weed-free period was significantly increased. The constructed models for Critical period of weed control in Dragon’s head showed that in order to prevent grain yield loss of 10%، weeds must be removed from the field after 19 until 55 days after crop emergence، and during 36 days respectively.