Burndown systems with residual activity for fallow areas infested with fleabane

This work aimed at evaluating the burndown efficiency of sequential applications of herbicides on Conyza spp. in areas that remained in fallow during the winter, as well as at monitoring the residual effect of herbicides in soil on weed control within soybean cycle. The experiment was carried out in a field where soybean was the previous summer crop and that remained non-cultivated during the winter. All herbicide treatments were composed by two burndown sequential applications: the first by spraying a tank mixture of glyphosate+2,4-D and the second by tank mixtures composed by glyphosate plus one or more herbicides with residual activity in the soil (chlorimuron-ethyl, flumioxazin and diclosulam). Evaluations included the burndown efficiency on emerged fleabane (plants ≥ 20 cm and plants < 20 cm) and the residual effect of herbicides on the new fluxes of morningglory and sida. Soybean was sowed five days after the second burndown application. One single application of glyphosate+2,4-D was sufficient to control completely fleabane plants < 20 cm. For plants ≥20 cm, tank mixtures of glyphosate plus either chlorimuron-ethyl or diclosulam in the second application prevented the occurrence of fleabane regrowth, without however eliminate them. Treatments containing herbicides with residual activity in soil (chlorimuron-ethyl, flumioxazin, chlorimuronethyl+ flumioxazin and diclosulam) were in suppressing the development of morningglory and sida.