Otherwise known as mikania micrantha, mile a minute is an invasive vine which can grow up to 9cm a day in summer, and has been a constant thorn in the ministry’s side.
But just before Christmas, ministry scientist Maya Poeschko and Quentin Paynter and Chantal Probst of Landcare Research made a discovery that made them extremely happy.
“We were releasing a new bio-control agent called puccinia arechavaletae, which was to control the balloon vine. It’s the first time that it’s been used as a bio-control agent anywhere in the world,” Paynter said.
“And whilst we were releasing this bio-control agent, we stumbled across the mile a minute rust, at one of the release sites where we released it in January this year.
“So even though we thought it hadn’t established, it obviously had, and it’s quite scattered and low-density at the moment, except one patch we came across where it was really devastating, and clearly it’s only just started going after the recent rains.”
Poeschko admitted that she had been giving up hope, so when Paynter and Probst found that the bio-control agent (puccinia spegazzinii) was successful they were dancing and screaming and hopping along the road.
“They were saying ‘Maya, you won’t believe it’. It was amazing. I must admit that I was giving up,” Poeschko said.
“Quentin never gave up, even though the last time we released it in the field was January. It was a great feeling.”
Previous surveys to check whether it had become established failed to detect the rust, which is easily overlooked when populations are at low density.
The rust is currently thinly spread over about 1ha, but a small patch was discovered where the disease was at very high levels, indicating that the population could be about to explode following recent rains.
One of the reasons that Paynter points to as to why there was trouble rearing the fungus was the heat, as it would struggle if the temperature did not drop below 25 degrees.
“Rust fungi do spread around in the weather. In fact, interestingly enough, whilst we were releasing the balloon vine rust, we stumbled across some cocklebur plants, and that was one of the other bio-control agents in this project.
“They were infected, and quite a long way from any of the release sites. So once the rust fungus is well established, it spreads around quite well in the wind.”
Paynter did point out that although the rust fungus will spread around the island, it will not make any impact on any unrelated species of plant.
The long testing and permit process, as well as the mile a minute rust fungus being the most heavily tested in the world, ensures that only the target weed will be affected.
Paynter said that they have been redistributing the rust fungus around different parts of the island, with aim of accelerating its spread.
“I would expect it to spread fairly quickly, although people might need to wait a year or two. It’s not something that you can rely on happening really, really rapidly.
“People just have to be a little bit patient. Based on what’s happened in other countries like Vanuatu, in a year or two, the mile a minute vine should be really sick throughout the island.
“It is a huge relief getting the mikania rust established, because mile a minute isprobably is the most important weed that we’ve been targeting in the Cook Islands.
“So knocking that one out is hugely satisfying.”