Collection time againFlea beetles have a role in the fight against leafy spurge.
By: Jonathan Knutson, Agweek
Darrell Deneke remembers the initial skepticism years ago about using flea beetles to control leafy spurge, one of the Upper Midwest’s most dangerous weeds.
“But biocontrols are pretty well accepted now. People understand that they work,” says Deneke, integrated pest management program coordinator for the South Dakota State University Extension Service.
Deneke and others have begun another annual flea beetle collection for use on leafy spurge. The beetles are collected with sweep nets in June or early July in places where they’re well- established, then transferred to other places where they’re needed. Because the spring was wet and cool, the beetle collection is beginning a week or so later than usual this summer.
It’s estimated that leafy spurge infests more than 2 million acres across the Upper Midwest.
Leafy spurge, which is toxic to cattle, can completely take over large areas of land. The weed reproduces through both a deep, extensive root system and explosive seed capsules that can be thrown as far as 15 feet from the parent plant.
Chemicals can control leafy spurge, particularly in cropland. But using herbicide on leafy spurge in pastures often isn’t cost-effective, officials say.
So in the 1980s and 1990s, efforts began in the Upper Midwest to control leafy spurge with beetles imported from Europe. Leafy spurge is native to central and southern Europe.
Deneke, who was county extension agent when the bugs were introduced in South Dakota, recalls that many people thought the effort would be futile.
Today, however, North Dakota, South Dakota, Minnesota and Montana all have established programs that use flea beetles to fight leafy spurge.
The bugs don’t make a major difference right away when they’re introduced to an area infested with leafy spurge. But over time, typically three to five years, newly hatched larvae of the insect feed on the leafy spurge roots and root hairs. That hurts the plants’ ability to utilize nutrients and makes them vulnerable to disease and winterkill.
The beetles don’t permanently eradicate leafy spurge; the weeds eventually return after the beetles use up their food supply and die.
To some extent, the bugs are a victim of their own success, Deneke says.
They’re most effective in large patches of thick, dense leafy spurge; more weeds mean more food, which leads to more bugs. While plenty of leafy spurge remains (309,420 acres in South Dakota alone), “Most of the big patches of yellow (leafy spurge) are gone,” Deneke says.
With fewer big patches remaining, it’s more difficult to collect large numbers of bugs at one location and transfer them elsewhere.
Some landowners also feel less urgency in utilizing the beetles because leafy spurge patches aren’t as big, Deneke says.
On the other hand, rising land prices provide more incentive to control leafy spurge, he says.
Want more information?
To learn more about using flea beetles to control leafy spurge:
• South Dakota — Contact Deneke at 605-688-4595 or Mark Rosenberg, extension field specialist/weeds at 605-626-2870.
• North Dakota — Contact your local county extension agent or weed control officer.
• Minnesota — Call your county agricultural inspector or the Minnesota Department of Agriculture and explain that you have leafy spurge on your land and are interested in using biocontrols.
• Montana — Start with the Montana Weed Control Association, www.mtweed .org.