Moldavian balm (Dracocephalum moldavica L.) essential oil content and composition as affected by sustainable weed management treatments

Abstract

In sustainable production of medicinal and aromatic plants, reduction in herbicide application rate and using straw mulch could be used as strategies for integrated weed management. The field study was carried out to evaluate the effects of herbicides reduced rate integrated with straw mulch on sustainable weed management, essential oil (EO) content and composition of Moldavian balm (Dracocephalum moldavica L.). The experiment was done in Agricultural Research Station of University of Tabriz, Iran, from April 2016 to July 2017. The treatments were consisted of two herbicide rates including recommended rate (R) and reduced rate (50 % R) of trifluralin and pendimethalin, integration of all herbicide treatments with mulch application (5 t ha−1) and mulch application alone. The effect of weed management treatment was significant on weed density and biomass and Moldavian balm dry weight and EO yield. Among the weed management treatments, the lowest weed biomass (17.1 g m-2) and the highest EO yield (22.51 kg ha−1) were observed in trifluralin R + mulch (TR + M) treatment. Integration of all herbicide treatments with straw mulch reduced the weed density and biomass and increased the Moldavian balm dry weight and EO yield, significantly. Generally the weed control efficacy of trifluralin was higher than that of pendimethalin. Gas chromatography - mass spectrometry analysis showed that the main constitutes of EO were geraniol, geranial, geranyl acetate, neral, nerol and neryl acetate. The contents of main components were influenced by weed management treatments, differently. The highest content of geraniol (41.4 %) and geranial (24.7 %) were obtained in TR + M and pendimethalin R + mulch (PR + M) treatments, respectively. Integration of all herbicide treatments with straw mulch increased the geraniol content and reduced the geranyl acetate content in EO. The weed density and biomass and Moldavian balm EO yield in trifluralin 50 % R + mulch (T50R + M) treatment were not significantly different with those in trifluralin R (TR). Therefore TR treatment could be replaced with T50R + M and recommended to medicinal plants growers as a more sustainable weed management method in Moldavian balm production.