They’re slow workers, but spurge-eating beetles can have a big impact on infested pastures and hay land
Having found a beetle with a taste for leafy spurge, researchers are now trying to figure out how to get the insects to gobble up more of the noxious, invasive weed.
Agriculture and Agri-Food Canada researchers from Brandon Research Centre are in the final year of a three-year study of beetles chowing down on leafy spurge at the Langford Community Pasture and the Elbow Community Pasture near Elbow, Sask. It’s part of a decade-long look at how well the beetles are doing at their job at these sites, said AAFC range management specialist Bev Dunlop.
“The main idea is to see how we can make this more effective,” said Dunlop.
The beetles were first released at the sites in the early 1990s. A decade later, researchers came by for a visit and noted spurge infestations had been knocked back by as much as 50 per cent. The decline is largely the result of plant stress inflicted in a one-two punch. Beetles lay their eggs at the base of the plant and while larvae feed on the plant’s root hairs, adults munch on its leaves.
One of the things researchers have been looking at, through weekly checks of about 60 beetle traps, is the time frame between when eggs are laid and emergence of adults. Knowing that would allow better integration with other methods of spurge control, Dunlop said.
“We’re looking at a more precise management technique with the beetles with everything else,” said Dunlop.
“We may have a better idea when to move the beetles so we’re not spraying at the same time we’re moving the beetles and stopping them from having the material to eat.”
Researchers also want to build up beetle populations and pass more insects out to landowners in Manitoba and Saskatchewan. That’s already being done in Alberta, which is also part of a Prairie-wide study of spurge-eating beetles.
“They’ve started a co-ordinated approach so that when beetles go to a particular farmer, that’s documented and monitored, and looked at in depth,” she said.
Sometimes that’s literally true — as spurge roots can go down nine metres and researchers have found larvae won’t go to those depths to get a meal. This is a problem with using beetles on sandier soils. Even under ideal conditions the trade-off from using beetles instead of herbicides is that the critters take a long time to do the job.
But there’s plenty of work for all.
A 2010 economic impact assessment by Brandon’s Rural Development Institute estimates there are now in excess of 1.2 million acres of leafy spurge in Manitoba, mostly in pastures, natural areas, hay or forage land, and roadsides. That’s triple what it was a decade ago.
The report’s authors estimated the economic impact in Manitoba at $40.2 million, including direct costs based on lost grazing capacity, nearly $5 million used for chemical applications on roadsides, and another $24.1 million in indirect costs.