Herbicidal potential onLolium rigidumof nineteen major essential oil components and their synergy

The phytotoxicity of nineteen major components of essential oils was determined using a perlite-based bioassay with rigid ryegrass (Lolium rigidum Gaudin). Specifically, germination and root length of rigid ryegrass under different concentrations of trans-anethole, thymol, linalool, carvacrol, carvone, fenchone, thujone, eugenol, trans-2-decenal, decanal, estragole, methyl cinnamate, eucalyptol, ocimen, limonene, myrcene, α-pinene, β-pinene or p-cymene were compared. Furthermore, the possible synergy or antagonism between these components was investigated. The phytotoxic dose–response effects of essential oils components were assessed by the Whole-range assessment method. Carvacrol, carvone, thymol, trans-anethole and linalool were the most phytotoxic components completely inhibiting rigid ryegrass germination and root length at 160 nL/cm3 or above. Fenchone, estragole, thujone, eugenol and trans-2-decenal provided intermediate inhibition, while myrcene, β-pinene, α-pinene, limonene, ocimene and p-cymene were slightly phytotoxic. Synergy between carvacrol, thymol, trans-anethole or linalool with carvone, thujone, fenchone, eugenol or eucalyptol was also observed. The results indicated that essential oils containing high concentration of specific components assessed in this work, such as carvacrol, carvone, thymol, trans-anethole or linalool, could be used in future as natural herbicides in the development of new weed control strategies. Also, these components activity could be further improved due to synergy with less phytotoxic components.