Beetle Wins Battle Against Pernicious Pasture Pest
Before and after: Landcare Research weed researcher Hugh Gourlay holds a healthy ragwort plant (right) and one attacked
by ragwort flea beetles. Thanks to these beetles, ragwort, once a serious invasive weed, has been reduced to a mere
nuisance.
Photo: Robert Lamberts, Crop & Food Research
A tiny beetle is winning the war against one of New Zealand’s most economically damaging weeds.
Ragwort (Senecio jacobaea) replaces pasture, and contains toxins that can cause fatal liver damage to cattle, horses,
goats and deer. It reduces butterfat, milk and meat production, and can taint the flavour of milk and meat, and even
honey. Ragwort can also be harmful to humans if ingested in sufficient quantities, or when weeded out by hand over an
extended period.
In the 1930s, a spate of exploding trousers ensued as farmers desperate to improve pasture production sprayed the
“miracle” weedkiller sodium chlorate – which reacts with natural fibres like wool and cotton in work clothes. Garments
detonated with the slightest heat or spark – sometimes with people inside them. But packing even more of a punch, and
much more safely, is the mighty ragwort flea beetle, introduced in 1983. Its caterpillars eat ragwort roots, thereby
killing the plants.
Landcare Research weed researcher Hugh Gourlay says field experiments found that the beetle achieved a 95% reduction in
ragwort within two to ten years of its release in both North Island and South Island sites. “Also, we started hearing
anecdotally how ragwort was disappearing, and so we asked around.
“We have had stunning reports of the flea beetle’s success from farmers and council staff around the country. We knew
the flea beetle was capable of being a great biocontrol agent. The stories we heard show how truly beneficial biocontrol
can be.” (See following testimonies.) Mr Gourlay says the success of the flea beetle represents a very high cost–benefit
return.
“A United States study has shown that for every $1 invested by the government in biocontrol $13 was returned to the
taxpayer, and that is likely to be similar here. We get the benefits of higher pasture, meat and milk production, and
improvement in the quality of milk and meat that do NOT contain toxins from ragwort.
“Also, the benefits go beyond the purely economic. We cannot put a price on an improved environment where ragwort has
been removed and native species allowed to regenerate.”
The flea beetle has succeeded around the country except for the West Coast and Southland, and to a lesser extent
Northland, for reasons not yet fully understood. Landcare Research is trialling two new insects that feed in similar
ways to the flea beetle, but are better adapted to these wetter climates.
Mr Gourlay says ragwort will never be eradicated from New Zealand entirely. “However, with vigilance it can be reduced
to a minor nuisance pest plant.”
Ragwort is at its most obvious now when its masses of bright yellow flowers can be seen on the roadsides and on farms.
Some district and regional councils send reminders at this time of year for local farmers to be particularly alert to
the need for ragwort control.
In the meantime, ragwort flea beetles are now coming out of their summer hibernation – ready to munch on any remaining
ragwort near you.
ENDS – RAGWORT REPORTS FROM COUNCIL STAFF THROUGHOUT THE COUNTRY FOLLOW. For more information, please contact: Hugh
Gourlay, Landcare Research, Lincoln, Canterbury (03) 325 6700 x 3748 021 239 2243 GourlayH@LandcareResearch.co.nz
The Beetles’ Greatest Hits – testimonials (from North to South): “Ragwort flea beetle numbers have been at good levels…
and have provided good ragwort control on most properties.” Greg Hoskins, Biosecurity Officer, Auckland Regional Council
(South-western Rodney)
“Like so many others in my line of work, I have always dreaded the holiday period because of the numerous complaints and
nasty phone calls that lovely little yellow flower caused. This year there haven’t been any, because there is no ragwort
in the Western Bay of Plenty.” Walter Stahel, Plant Pest Officer, Environment Bay of Plenty
“This season I found two areas that have been ragwort hotspots – wall to wall yellow – where no herbicide spraying was
ever done, suddenly completely devoid of ragwort plants. I attribute this collapse to the flea beetle, which was
introduced six years ago.
“The flea beetle has now reached every corner of the Opotiki district.” Tim Senior, Environment Bay of Plenty Plant Pest
Officer
“Jim Laurenson, the local biosecurity officer, released flea beetles onto my property and I said he was a fool to do so.
Ten years on, I went back to shake his hand and say thanks. I continue to spray and grub my ragwort, but it really isn’t
a problem anymore.
“I now use less than five litres a year of chemical to control my ragwort and thistle weed. My neighbours now collect
hundreds of my flea beetles for use on their own properties.” Steve Fagan, Farmer, Hangatiki, Waikato
“A combination of flea beetles, compliance with noxious plants enforcement and pasture fertility improvement has reduced
ragwort infestations to the point that the plant is not the problem weed it once was.” Brian Calkin, Inspectorate
Manager, Taranaki Regional Council
“Southern Manawatu was once a sea of yellow, but now most properties are free of ragwort.” Neil Mickelson, Plant Pest
Officer, Horizons Regional Council
“Ragwort flea beetles have been growing in numbers, and ragwort seems to be completely gone from the area.” Robert Quan,
Plant Pest Officer, Greater Wellington Regional Council
“In practical terms, ragwort, once a serious invasive plant, has been reduced to a mere nuisance.” Ben Minehan,
Biosecurity Officer, Marlborough District Council
“Before the ragwort flea beetle, ragwort was quite widespread throughout North Canterbury. The Leader and Waiau
riverbanks were thick with ragwort, as were some of the neighbouring grazed pastures. Ragwort was also a major problem
on the dairy flats of Kaikoura.
“Ragwort populations throughout North Canterbury including Kaikoura declined quite rapidly within three to five years of
the flea beetle’s release in the early 1980s.
“The ragwort flea beetle has been an amazing success story that has saved many farmers many dollars on herbicide
control, and saved our countryside from being doused with environmentally unfriendly chemicals.” Lawrence Smith,
Biosecurity Team Leader, Environment Canterbury
ENDS