As we experienced with the Taro Leaf Blight outbreak in the 1990s, the introduction of exotic pests or diseases into Samoa can have disasterous effects on our people and on our economy.

Water lettuce is a free floating aquatic plant in rosettes of green leaves, rosettes occuring singly or connected to others by short stolons whose origins are uncertain. It forms large, dense floating mats. The plant can adapt to life in ponds, dams, lakes and quiet areas of rivers and streams, but cannot withstand salt water. Still continue with observation whether it is to survive in winter.

Poster or infographic on invasive plants in the Cook Islands.

Wedelia, creeping oxeye, or the trailing daisy, a deceptively beautiful, bright emerald-green creeper with bright yellow daisy-like flowers, is one of the world's most aggressive weeds and is listed among these other destructive organisms as one of the worlds 1000 worst invasive alien species. IT is now firmly established in Melanesia and throughout the Pacific islands.

As our global economy grows and the boundaries between nations shrink, we face new social, environmental, and economic challenges.

The papers in this volume were, with a few exceptions, presented at the third Island Invasives conference, held in Dundee, Scotland in July 2017. The papers demonstrate up-scaling in several aspects of eradication operations – not least in ambition, land area, operational size, global reach and of course financial cost. In the space of a few decades, the size of islands treated for invasive species has increased by five orders of magnitude – from a few hectares to over 100,000 ha or 1,000 km2.

Biological control of introduced weeds in the 22 Pacific island countries and territories (PICTs) began in 1911, with the lantana seed-feeding fly introduced into Fiji and New Caledonia from Hawaii. To date, a total of 62 agents have been deliberately introduced into the PICTs to control 21 weed species in 17 countries. A further two agents have spread naturally into the region. The general impact of the 36 biocontrol agents now established in the PICTs ranges from none to complete control of their target weed(s).

Invasive weeds are one of the most serious threats to biodiversity and sustainable development in the Pacific region. Biocontrol is likely to be the only feasible way of managing many widespread weeds, but is not always appropriate or successful. With so many weed species to tackle and inevitably limited resources, prioritising where to direct control efforts most effectively is of key importance. Landcare Research recently developed a framework for the Australian government that allows the best and worst weed targets for biocontrol to be identified.