Tiny beetle ravages ragwort
Ragwort’s distinctive bright yellow flowers used to be a familiar sight across New Zealand farmland. But thanks to a tiny flea beetle the weed, which is particularly toxic to cattle and horses, is now largely under control saving farmers millions in control costs.
Waikato dairy and beef farmer Steve Fagan was sceptical to say the least when tiny beetles were released on his farm about 25 years ago to control ragwort.
“When Jim Laurenson, the local biosecurity officer, released flea beetles onto my property I said he was a fool to do so. I thought it was a big joke.”
But he would later eat his words.
“Ten years on, I went back to shake his hand and say thanks,” Steve said.
The ragwort flea beetle or
Sea of yellow
The weed has now almost disappeared from the Fagan’s 1000 acre Hangatiki property, but the beetles are still there.
“Six months ago I actually noticed beetles on the odd remaining ragwort,” Steve said.
His wife Maxine said the farm, which they bought 42 years ago, used to be overrun with ragwort. Looking at the lush green pastures, full of clover, it’s hard to imagine.
“We had what we would call a ragwort farm,” she said.
“We had to use a rotary crusher to cut tracks for the cows. That’s how bad it used to be,” Steve said.
The family lost several cows to the weed.
“No one wanted to buy the farm when we brought it because it had so much ragwort,” Maxine said.
The couple used to spray the weed with chemicals daily to try and get it in check. But this not only killed the weed but the grass.
“We’d milk early, milk late, and spray all day. We’d spray 2500 litres most days to try and get it under control. We thought we’d never get rid of it. It cost thousands.
“We even tried running sheep but they only made it grow thicker. It nearly broke us,” Steve said.
“These days it’s more about milking the cows. We still have the odd ragwort, but we used to have paddocks of it.”
Maxine said news of the biocontrol’s success spread fast in the community.
“Cars lined up our road all coming to get the beetle."
Hugh Gourlay, a weed biocontrol expert at Landcare Research, said seldom did a biocontrol agent work as quickly as the flea beetle.
Some areas where the flea beetle had been released were almost clear of ragwort in as little as two years, he said.
“Within about 10 years, in most drier climates around New Zealand where we had released the beetle, ragwort had pretty much disappeared. That was a huge success in terms of biological control.”
The adult flea beetle’s feed on the leaves making small round holes but the larvae actually do the most damage. They feed in the roots of ragwort and kill the plants at the rosette stage, he said.
But the flea beetle didn’t prove a solution for every region, struggling in wet areas where rainfall exceeded 1600mm/year.
As a result, the weed continued to persist particularly on the West Coast, as well as Southland, parts of Otago, and the central North Island.
Undeterred, the West Coast community rallied, and with Gourlay’s help established the West Coast Ragwort Control Trust (WCRCT). The group was granted funding by the Ministry for Primary Industries Sustainable Farming Fund to search for another biocontrol agent.
Gourlay and his colleagues discovered a plume moth that was proving successful in controlling the weed in wet conditions in Australia. In 2005, the moth was released after extensive testing.
“Three to five years later we had the same result we had with the flea beetle, ragwort populations started disappearing,” Gourlay said.
“Between the two agents almost throughout New Zealand ragwort has become relatively rare.”
Areas where ragwort continues to persist are those where the plume moth has yet to be established or spraying is preventing biocontrol agents from doing their thing, he said.
Dr Simon Fowler, who leads Landcare Research’s Beating Weeds Programme, said tales from farmers like the Fagan’s and site visits had showed the flea beetle was working. What wasn’t known was how much it was saving farmers across the country. A 2005 survey conducted by the WCRCT provided the means to find out.
The survey outlined how much farmers were spending controlling the weed using conventional methods as the flea beetle had failed to thrive in the region due to the wet climate. That figure was then extrapolated across the 12,000 dairy farms in New Zealand, Dr Fowler said.
“That gives us a costing if biocontrol hadn’t of happened,” he said.
“The figure took us all by surprise.”
The study found the flea beetle was saving dairy farmers $44 million in control costs alone every year.
“In only a few years that would cover every dollar that New Zealand has spent on weed biocontrol research many, many, many times over. And, of course, if we had figures beyond the dairy industry it would be even greater. Our study shows we could save a further $20 million a year if the plume moth is successful, and it’s already starting to look pretty good.”
Way back in the 1930s the flea beetle was rejected by New Zealand as a potential biocontrol agent because its impact was thought to be low. Back then, a few simple experimental trials would have demonstrated the potential of the flea beetle for ragwort control, Dr Fowler said.
“Our analysis shows that a small investment in science nearly 90 years ago would have saved the New Zealand dairy sector a staggering $8.6 billion.”
The quantitative study was funded by the Ministry of Business, Innovation and Employment as part of Landcare Research's Beating Weeds Programme.
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