A revised weed prioritisation tool

In 2022, our framework for prioritising weed biocontrol targets was redeveloped to incorporate a new system for scoring weed importance alongside previous developed scoring tools that predict the potential impact and cost of a biocontrol programme. This resulted in a 3-factor decision making system for weed biocontrol target prioritisation in New Zealand based on:

Weed importance. Scored according to a weed’s distribution (i.e., widespread weeds score more than localised species), socio-political pressure to control, ecosystem impacts summed across a variety of habitats (species that can transform ecosystems scoring highest), and ease and cost of control using conventional methods such as chemical and mechanical control (weeds that are difficult and expensive to control are considered more important targets than weeds that can be easily and cheaply managed with existing tools).
Likeliness of Biocontrol success. This was estimated using the plant traits model
Cost of implementing biocontrol. Pioneering programmes cost about 4.2 times more than repeat programmes (programmes that have already been implemented against the same weed overseas), and costs increase as the number of agents required increases.

The prioritisation tool was used to rank 158 weeds using a formula that multiplied the weed importance score by an overall biocontrol score that predicts ‘bang for buck’ (i.e., biocontrol success score divided by the cost of implementing biocontrol score). It provides a far superior system to what was previously used to guide funding decisions for weed biocontrol. But the tool is only as good as the information provided. It is crucial that information used to rank weeds is kept up to date and the rankings regularly reviewed, since these could change dramatically with new information such as the success of new programmes overseas. By following and refining this prioritisation approach it is hoped to see a tangible benefit through increased cost-effectiveness and transparency around target selection for biocontrol work in the years to come.

A revised weed prioritisation tool

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