response of barnyardgrass [echinochloa crus-galii (l.) p. beauv.] and velvetleaf (abotilon theophrasti medicus.) to glyphosate and nicosulfuron herbicides under greenhouse condition

abstract to study the efficacy of glyphosate and nicosulfuron herbicides on barnyardgrass [echinochloa crus-galii (l.) p. beauv.] and velvetleaf (abotilon theophrasti medicus.) control and to find the ed50 index, experiments were conducted as factorial arrangement of treatments 2×7 based on completely randomized design with six replications for each weed in 2008-9 at research greenhouse, ferdowsi university of mashhad. glyphosate and nicosulfuron herbicides applied to 3-4 leaves of weeds as post-emergence at 0, 0.125, 0.25, 0.5, 1, 2 and 3 lha-1 product (0, 51, 102, 205, 410, 820, 1230, and 0. 5, 10, 20, 40, 80, 120 gai ha-1, recpectively). the results showed significant effect of herbicide dosages on visual assessment, survival percentage, plant height, leaf area, and shoot dry weight of weeds (p≤0.01). dose response curves of barnyardgrass biomass for both herbicides were similar, but velvetleaf biomass showed different responses to herbicides. so that, 50 percent reduction of velvetleaf biomass (ed50) required 1.6 fold nicosulfuron herbicide incomparison with glyphosate herbicide. also, control percentage curves of weeds changed with glyphosate higher slope than nicosulfuron, that emphasized the results of dose response curves. based on the amount of ed50 obtained for each herbicide in greenhouse conditions that is differ from the farm reports, it can be concluded that the effect of herbicides under field and controlled conditions was not the same and can not be recommended from dosage for greenhouse tests. according to the proper correlation between the mean of shoot dry weight and weed control percentage (r2=0.98**), it seems that using the values of this index (based on visual assessment) for evaluation of herbicides effect on weeds instead of dry biomass could be useful as well.