A formulation is provided for application to a host plant to reduce, inhibit or impair one or more of growth and development of the host plant. A method of inhibiting growth plant growth and development is also provided as a means of controlling weedy species. The method comprises: selecting a suitable gene for growth suppression in a target plant identifying an at least one target site accessible to base pairing in the suitable gene identifying an at least one divergent site in the at least one target site designing a construct complementary to the at least one divergent site adding an at least one RNAi inducer to the construct and delivering the construct to the target plant.
