Evaluate the Efficacy of pelargonic acid and lemongrass essential oil for the control of different weed species

Natural herbicides can contribute to reduce the use of chemical herbicides but information on their efficacy is still limited. Greenhouse and field experiments were conducted to evaluate the herbicidal efficacy of pelargonic acid and lemongrass essential oil on several weed species under different environmental conditions. Lemongrass essential oil had almost no phytotoxic effect, but it was not possible to assess whether this inactivity was due to the specific chemical composition or formulation of the essential oil used in this study. Pelargonic acid achieved a partial herbicidal effect, with different species-specific sensitivity levels among the tested weeds. Grass weeds, in particular A. myosuroides and L. rigidum, were more tolerant to pelargonic acid, with no mortality and limited biomass reduction even at the highest application doses. The large difference in sensitivity was observed also among dicots weeds, with P. oleracea and A. Theophrastus being more tolerant than C. sumatrensis and S. nigrum, on the base of specific leaf traits as leaf angle, leaf hairiness, or wax layer on the cuticle. Furthermore, environmental conditions have been proven to affect the herbicidal efficacy of pelargonic acid in different simultaneous ways. Hot and dry conditions can indeed promote weeds leaf traits that reduce sensitivity to pelargonic acid and reduce the persistence of spray droplets on the leaf surface, limiting herbicide penetration inside weed leaves and consequently hindering its efficacy. Despite its high cost, pelargonic acid can therefore be a useful tool in a multi-tactic strategy for sustainable weed management while its use as a stand-alone tactic is less recommendable.