Natural herbicides approved in organic agriculture are primarilynonselective burn-down essential oils applied POST. Multiple applicationsare often required due to their low efficacy. To address this problem, thein vivo herbicidal activity of manuka oil, the essential oil distilled frommanuka tree (Leptospermum scoparium J.R. and G. Forst), wastested on selected broadleaf and grass weeds. While manuka oil exhibitedgood POST activity when applied in combination with a commercial lemongrassoil–based herbicide, it ultimately demonstrated interesting PRE activity,providing control of large crabgrass seedlings at a rate of 3 L ha−1. Manuka oil and its main active ingredient,leptospermone, were stable in soil for up to 7 d and had half-lives of 18and 15 d, respectively. The systemic activity of manuka oil addresses manyof the current limitations associated with natural herbicides. Additionally,its soil persistence opens up a multitude of new possibilities for the useof manuka oil as a tool for weed management and may be a potential bridgebetween traditional and organic agriculture.
