The importance of weeds in plant biosecurity

Weeds constitute a unique biosecurity challenge. We describe the causes of plant invasion and pathways for introduction. The broad and diverse impacts of weeds are described as well as what makes them different from other types of pests for risk assessment and management along the biosecurity continuum. We offer a policy focus and a look at pre-border and post-border risk management strategies. We describe the Weed Risk Assessment approach and its increasing adoption and the importance of recognising future weed threats in the context of climate change. We describe early detection and rapid response in the context of novel plants and how to know when to eradicate versus contain outbreaks. Integrated and adaptive management options are also discussed in the specific context of the long-term perennial impacts of weeds, with a particular focus on biological control. Finally we discuss how weeds are often controversial by having both harmful and beneficial impacts across different sectors and the challenges this raises for both regulation and management. We finish the chapter with a selection of case histories aimed to illustrate the complexity and diversity of issues that surround the perceived undesirable interactions between exotic plants and societal values.