The rust called Uromyces pencanus was introduced in a controlled release programme by Landcare Research firstly near a vineyard in Marlborough’s Blind River area and then at another site near Cheviot earlier this month.
This follows a long process including gaining a permit from Argentinian authorities to export the rust from its native range and then it being approved for release by the Environmental Protection Authority (EPA) in July.
Chilean needle grass is a weed from South America with sharp penetrating seeds that can cause blindness in livestock, pelt and carcass damage, and the loss in pasture quality leads to farm production taking a financial hit.
If allowed to spread to its full range, specialists estimate it would cost the economy up to $1.1billion a year with its potential climatically suitable range covering 3.96 million hectares.
Infestations are confirmed in Hawke’s Bay, Canterbury and Marlborough.
Landcare Research says the rust fungus only attacks the strain found in Marlborough and Canterbury with another fungus yet to be uncovered for Hawke’s Bay populations.
Biocontrol knowledge broker Dr Rowan Sprague said a small population was successfully released near a vineyard near Blind River and then near Spotswood in North Canterbury on October 15.
"Only just recently we have done the first release and we’re pretty sure this is the world-first release of rust fungus biocontrol for Chilean needle grass."
The biocontrol release would be followed by a return to the site likely in autumn to check if it had successfully established and for signs of new infections, she said.
"It’s an infection process with the rust going inside Chilean needle grass leaves and as it grows it will burst through the leaf surface to produce these dark brown powdery rust pustules. As the rust is growing inside the leaf it’s draining energy from the plant and when it bursts through it releases spores. The idea is especially in dry sites the wind will spread the spores around and they will land on new Chilean needle grass leaves and start the infection process all over again."
The natural process was free of herbicides with the sites kept spray-free of herbicides or mowing as the host plants needed to be unharmed so it could be at its most effective, she said.
"As with all biocontrol it’s not the only solution and it’s not the silver bullet, but it can help control and limit the plant so it won’t be such as huge problem. We are hoping it will keep Chilean needle grass more in check."
Bags are creating shelter for the rust spores to keep the area moist and help with its germination.
Further biocontrol agents are not on the horizon at this stage.
Dr Sprague said Chilean needle grass was a big animal welfare concern and a production pest as it invaded and out-competed pasture species.
She said the programme had been a long time in the making over 30 years.
"It started back in the 1990s in Australia. Australia was looking into biocontrol agents for Chilean needle grass and nassella tussock and agents in the native range of Argentina. New Zealand joined the programme in the early 2000s and there were quite a few challenges."
Among them, stubborn fungi resisted cultivation for host range testing and by the time EPA’s predecessor approved the release of the rust fungus in 2011, Argentinian export regulations prevented export of the rust to New Zealand.
Dr Sprague said the export permit authorised by Argentina in 2023, followed by rigorous host testing to make sure the biocontrol agent would not attack other plants and approval by the EPA had been a breakthrough.
Host testing included three native grasses closely related to Chilean needle grass.
The overall work was funded by the National Biocontrol Collective and the Ministry for Primary Industries.
Future work would focus on finding effective strains for North Island populations.
