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Marrying classical with inundative weed biological control

Marion Seier: CABI

<div>Traditionally, classical and inundative weed biocontrol have been considered as two separate approaches. The former targets invasive alien weeds by releasing exotic, co-evolved and host-specific natural enemies from the weed’s native range to achieve self-perpetuating control; whilst the latter aims to increase the efficacy of a native agent by repeated mass application of high concentrations of infective propagules to create an epiphytotic. However, this distinction can become blurred when a classical agent is applied inundatively against an invasive weed, such as the rust <em>Maravalia cryptostegiae</em> against rubbervine (<em>Cryptostegia grandiflora</em>) in Australia, or when a pathogen strain from one country is licensed as a bioherbicide in another. The leaf-spot pathogen <em>Mycosphaerella polygoni-cuspidati</em> on Japanese knotweed, however, represents a unique example of marrying the classical and inundative approaches. This Japanese fungus had been considered as a classical agent for the weed in both the UK and Canada, but was disregarded due to potential impacts on native plant species. However, <em>M. polygoni-cuspidati</em> is heterothallic, lacking an asexual morph and able to infect via mycelial fragments. This offers the opportunity for mass production and targeted single-mating type inoculum application, whilst preventing reproduction, persistence and spread of the agent in the environment.</div>