control of redroot pigweed in greenhouse with oxyflourfen and determining the rate and time of this herbicide in controlling soybean weeds

in order to investigate the efficacy of split, reduced and whole rates of oxyfluorfen in controlling redroot pigweed (amarnthus retroflexus) and also to evaluate possible soybean (glycine max) injuries a experiment was conducted in research greenhouses of karaj collage of agriculture, university of tehran in 2005. treatments included oxyfluorfen doses at 0.25, 0.5, 0.75 and 1 l/ha in one stage spraying (3-4 foliage redroot pigweed, v2 soybean) and split values 0.25+0.25, 0.35+0.35 and 0.5+0.5 of this herbicide in 2 stages spraying (first stage was before noted time, and second stage was 2 weeks after first spraying). results revealed significant differences between herbicides treatments with redroot pigweed dry weight, soybean biomass and yield, and percentages of injury 2 weeks after treatment. the highest reduction for all above attributes was observed at 1 lit/ha. oxyfluorfen at this dose controlled redroot pigweed by 90%, but also reduced biomass and yield of soybean by 50%. all split rates reduced weed biomass as much as whole rates did. however, soybean yield reduction was lower at split rates than those of whole rates. reduced rate of 0.25 l/ha had no significant effect on both weed and soybean. applying split rate of oxyfluorfen at 0.35 l/ha twice at biweekly interval was the most efficient treatment. herein, although the dry weight of weed was reduced by 80%, soybean yield decreased only 20%. in addition, in order to investigate the appropriate rate and time of application of oxyfluorfen for soybean weed control a field experiment was conducted at the research farm of collage of agriculture of university of tehran during 2004-2005. treatments included oxyfluorfen at 0.75, 1 and 1.25 l/ha at soybean growth stages of v2, v3 and pre emergence (pre). weed free and weedy treatments were also included. there were significant differences between treatments with weed density and dry weight. oxyfluorfen applied pre at 0.75 l/ha had the lowest efficiency (72%) to reduce weeds dry weight, followed by oxyfluorfen at 1.25 l/ha when applied at v2 soybean growth stage. in most treatments due to the phytotoxic effects of herbicide on soybean, the seed yields even were lower than whole season weed infested treatment. finally, the highest seed yield (1972 kg/ha) was achieved at 0.75 l/ha when applied at v2 soybean growth stage.