TECHNICAL
FLATTENING THE CURVE – HORTICULTURE STYLE Eve Pleydell : HortNZ risk policy advisor
Area affected
S VA IN
PREVENT
• Invasive species totally absent from environment
ERADICATE • Small number detected
CONTAIN • Increased abundance • Limit spread
N IO
E RV CU
CONTROL • Species widespread & abundant • Long-term management required
Management costs
INVASION TIMELINE
• Eradication possible
The invasion curve describes the arrival and spread of a new invasive species and the management actions required at each stage
Figure 1: An invasion curve showing how control options change as the size of an invading pest population increases over time and across larger areas of a country. In reality, knowing when eradication is no longer feasible or when long-term management is the only real option left is not straight forward. Image sourced from Invasive Species Council, Australia. Invasion-Curve – Invasive Species Council
If a new plant pest enters the country, everyone one wants to get rid of it as fast as possible but sometimes eradication is not possible. What can growers do to help flatten an invasion curve? Key points • Eradication of an invasive pest or disease is not always feasible. • Alternative options include trying to contain or manage the pest. • At all stages of the invasion curve growers can minimise the risk to and impacts on their business by using good on-farm biosecurity practices. In New Zealand we are fortunate to be free from many pests and diseases that occur in other countries. To protect this status and support our primary industries we impose some of the strictest biosecurity border controls in the world.
However, as the international movements of people, goods, and mail increases, our country is coming under greater invasion pressure from unwanted pests and diseases and it is not possible for border controls alone to provide 100 percent protection. When an invasive plant pest is detected in New Zealand for the first time, the Ministry for Primary Industries (MPI) works with the affected sector to control the local situation, assess the national situation, and decide on the best control strategy. While eradication of the pest is often the most desirable outcome, the chances of eradication being successful decreases as the length of time the pest has been here and the geographical distance it has spread over increase. Eradication is also more difficult if the pest is biologically programmed to be a successful invader. For example, pests capable of spreading across long distances fast, or that reproduce rapidly, or that are hard to detect early are likely to be more challenging to eradicate. Think of the difference between the original strain of Covid-19 that as a country we successfully eliminated
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