High nutritive content, using in various industrial sectors and adaptation of various regions of sunflower ( Helianthus annuus L.) have allowed of cultivation and consumption at high scale. One of the important problems of sunflower prevalently cultivated in Marmara and Central Anatolia Regions is weeds. Among the weeds, common cocklebur ( Xanthium strumarium L.) is very important because it has a competitive character, and there is only one herbicide registered to control this weed. The field study was carried out to determine the economic threshold of common cocklebur in sunflower from 2013 to 2015 in Ankara. According to the three-year study values, the highest sunflower plant length (138.33 cm), head diameter (14.4 cm) and 1000-seed weight (85.03 g) were obtained from the control parcels while the lowest plant length (104.17 cm), head diameter (10.41 cm) and 1000-seed weight (62.81 g) were taken from the parcels consisted of 16 common cocklebur plants. The economic thresholds were calculated using the current sunflower price and the herbicide, imazamox (40 g l -1 SL), price. The economic threshold in 2013, 2014 and 2015 were computed as 1.22 plant m -2 (Y=-7.139x+142.23), 0.61 plant m-2 (Y=-8.041x+145.84), 1.97 plant m -2 (Y=-9.78x+140.26). To control common cocklebur economically in Ankara herbicide applications should be done when the intensity of common cocklebur reaches the values, 0.61-1.97 plant m -2 .
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