Essential oils for preventative treatment and control of Asian soybean rust

The objective of the work was to evaluate the effect of essential oils as a preventive treatment to control Asian soybean rust. Initially the fungitoxic effect of the essential oils of Hyptis marrubioides, Aloysia gratissima and Cordia verbenacea was tested on the urediniospores of Phakopsora pachyrhizi, through in vitro tests. The in vivo test was set up in a greenhouse, using cultivar MGBR-46. The treatments consisted of the three oils at different concentrations, a fungicide based on pyraclostrobin + epoxyconazole and a control. To verify the potential of the essential oils in preventive treatment, inoculation was conducted at 0, 6, 12 and 24?h intervals, after application of the treatments. All treatments inhibited 100% of Phakopsora pachyrhizi germination. In the in vivo test, it was observed that all of the oils were efficient in controlling soybean rust, by preventive treatment, mainly at the higher concentrations. Efficiency of the oils was reduced with the increase of the interval between the application of the treatments and the onset of the pathogen. The essential oils, at the tested dosages, were not as efficient as the pyraclostrobin + epoxyconazole based fungicide.