Root-knot nematodes constitute a major constraint to agricultural production worldwide. They are particularly devastating in the vegetable industry in the tropical world. Management strategies such as cultural, biological, physical and host resistance have peculiar limitations. Chemical control however is most effective, but the effect of synthetic pesticides on the environment raises serious ecological concerns. Active ingredients identified in the African marigold have nematicidal properties and highly lethal to root-knot nematodes. In this study, the effective stage of the African marigold in managing root-knot nematodes was investigated in plant house, laboratory and micro plots experiments. In all cases, the effective stage of the antagonistic plant corresponded to 8-11weeks of growth during which period population reduction was maximum, hatching inhibition was greatest and root gall index was lowest. This information is useful for integrated pest management (IPM) formulation and implementation. Agricultural researchers, extension agents, students and farmers would find this book most useful.