Twenty-two essential oils were tested over three years to examine how effective they were in controlling powdery mildew of flax when they were used as foliar sprays in an outdoor pot experiment. Certain oils exhibited an inconsistency trend across years with some were effective in controlling the disease and others were not. None of the tested oils failed in controlling the disease in all tested years. The cluster analysis grouping of the oils was unrelated to the taxonomic position of their plant sources. Onion, caraway, celery, and black cumin oils were promising for commercialization due to two reasons; firstly, they significantly reduced incidence and severity of disease each year, and secondly, they had no negative effects on seed and straw production.