Tolerance of common oregano (Origanum vulgare) to seven widely used post-and pre-emergence herbicides

Herbicides are often used to support weed control in herbicide-sensitive medicinal herb productions; however, the herbicide tolerance of these plants is less known. To reduce the chemical hazard risk, a study was conducted in 2018 at Hungarian University of Agriculture and Life Sciences, Budapest, Hungary, to explore the tolerance of the cultivated oregano to seven specific and widely used herbicides. In addition, the validity and usability of the applied bioassay procedures were compared for future methodological purposes. In laboratory and greenhouse studies, we applied three different bioassay tests, in which oregano leaves or plants were treated by different herbicides (i.e., glyphosate, MCPA, bromoxynil, oxyfluorfen, phenmedipham-desmedipham, propyzamide, pendimethalin). The tissue damage represented the level of sensitivity analyzed by doseresponse curve model fitting. The post-emergence herbicides such as MCPA, bromoxynil and glyphosate imposed a much higher technological risk for the oregano production than the others, such as pendimethalin, phenmedipham-desmedipham and oxyfluorfen, primarily used in pre-emergence technology, while the propyzamide was harmless. Nevertheless, all bioassays were considered to be valid, showing high repeatability, providing consistent tolerance ranks. The pre-emergence weed control could offer more, less harmful herbicide alternatives for the oregano farmers than the post-emergence technology. The applied bioassays could support the labour-intensive toxicological studies where the rapidity, accuracy and genetic control is especially crucial.