Mapping Invasive Species
Nassella tussock is an invasive grass that is spreading in Canterbury and elsewhere in New Zealand. It displaces productive pastures and is unpalatable to stock. Environment Canterbury’s biosecurity team spend months inspecting properties and ensuring landowners identify and control this pest plant and control its spread – a requirement of the Canterbury Regional Pest Management Plan. Mature Nassella tussock can produce up to 100,000 seeds, so it’s important to remove all infestations prior to viable seed being produced each year.
Working closely with Environment Canterbury, Prism teamed with Lynker Analytics to train an AI program to identify the pest plant from aerial imagery collected by a small plane with the support of the landowner. The machine learning model was trained by splitting up the large image into non-overlapping 512×512 tiles. This allows the programme to learn over time to identify a pixel or group of pixels as either ‘Nassella’ or ‘not-Nassella’.
Only 70 years ago, Nassella forced some farmers to leave the land after it ran rampant, taking over entire farms, leaving no room for crops or stock.
The model has been developed and applied across multiple farms now and results show the AI to have around a 90 per cent success rate at identifying large mature Nassella tussock. More refining of the model is required to increase that identification rate.
The benefits for the land owner and regional council in having AI identify pests through imagery mean greater efficiencies in identifying unknown infestations, and reducing the need for biosecurity staff to physically inspect the land as often.