the effect of wheat residue and trifluralin rates (%48 ec) on weed specises composition of sunflower (helianthus annuus) in birjand

abstract leaving crop residues on the soil surface may significantly affect the behavior and activity of herbicides. to probe this effect, a factorial experiment in a randomized complete block design with three replications was conducted using two factors including different rates of wheat surface residue (0, 1250, 2500 and 3750 kg ha-1 ) and different rates of trifluralin (%48 ec) herbicide (720, 1200 ,1680 g ai. ha-1) plus control (without herbicide use) in conducted at research field of agricultural faculty of birjand university in summer 2008. result showed that increasing wheat residue and also trifluralin concentrations reduced the density of hoary cress (cardaria draba), red root pigweed ( amaranthus retroflexus), common lambsquarter (chenopodium album) compared to the control during growing season. in contrast, the density of camelthorn (alhagi camelorum) was not influenced by either of experimental factors and their interaction. moreover, there was a synergistic effect between different rates of trifluralin and residue level of 1250 and also between 1200 g ai. ha-1 of trifluralin and residue level of 2500 kg ha-1 on reducing the density weeds compared to the control. residue level of 3750 kg ha-1 decreased herbicide efficacy.