How to Make Biocontrol Work Against Leafy Spurge

Dave Philips, MSU Extension agricultural agent in Fergus County and MSU faculty member, says technology has made his job easier—especially the information gathering component.

Leafy spurge will soon make its annual, albeit unwelcome,appearance on everything from range land to roadsides and railroad right-of-ways.

Bob Richard, director of the USDA-Animal and Plant Health Inspection Service's Plant Protection Quarantine and Biological Control of Weeds Laboratory in Bozeman, says a lot of the success depends on how, where and when initial releases of biological control agents are made.

"We now know a lot more about how to make the initial release, which agents work best in which situations, and how many insects should be released," Richard said. "By taking a few of these things into consideration, you can significantly boost your chances of making a successful release and getting a good population of biocontrol agents established."

Richard, an entomologist, has made more than 2,000 releases of the host specific Aphthona species leafy spurge flea beetle in a variety of habitats spread across 19 states during the past 12 years. More than 80 percent of those releases have resulted in established populations that are now contributing to leafy spurge control.

"Establishment is absolutely the key," Richard said. "If you don't get good establishment, you can't expect good control."

Don Kirby, a professor of Animal and Range Science at North Dakota State University said people also need to understand that biological control is a sustainable, long-term solution but not a "quick fix."

"Some people just aren't patient enough, and that's easy to understand - if you've got a leafy spurge problem, you want to get it taken care of NOW," Kirby said. "But biological control isn't going to work overnight - it's something you start with now to achieve inexpensive, permanent control in the future."

Some of the flea beetle release sites Kirby is studying are eight years old, but he said the results have been worth the wait.

"It's pretty impressive," he said. "We've seen dramatic reductions in leafy spurge stem densities - in some cases from 218 plants per square meter to five - and a corresponding increase in the production of desirable grasses."

The sites also provide a good example of why it's important to consider the long-term benefits biological control can provide, he added.

"Leafy spurge will never again be a deterrent to livestock production on these sites because the flea beetles will always be there," he said. "The flea beetles and spurge have reached a natural balance - if the spurge increases, flea beetle populations will increase and keep it under control.

The bottom line is simple: The sooner you get started, the sooner biological control will work."

Richard and Kirby offered the following generalities for increasing the chances of making a successful release of flea beetles:

  • Site location:

    Drier and sunnier is better, and some slope (to provide drainage) is a plus. "Flea beetles will move into shady, moist locations after a population is established, but we've learned that these are not good places to make an initial release," Richard said. There is also some variation according to species, he added. "Aphthona nigriscutis prefers a dry, sunny site while Aphthona lacertosa will tolerate a much broader range of locations."

  • Timing:

    Insects must be released before they lay eggs! "If you release insects too late in the season, they won't reproduce and there won't be any insects next year," Kirby said. Although timing depends on several factors, including geography, elevation and climatic conditions, anything later than mid-July is considered too late, Richard said.

  • Number of insects released:

    More is better. "Early releases generally consisted of 500 or fewer flea beetles, but we're now focusing on releases of at least 1,000," Richard said. "Releasing more insects enhances the chances of establishing a population."

Another common problem, Richard said, is that people often release insects at a site with lots of spurge but none of the other ingredients needed for a successful release.

"Again, people need to understand that successfully establishing a population is the key," he said. "If you can get a population started, they'll eventually move to the places where you most want or need control. But that may not be the best place to try and get a population started."

Richard admits he gets a little defensive when people say the insects failed to work.

"Failure is generally a result of how or where the insects were released," he said. "But we can now minimize establishment failure by using all of the things we've learned over the past 10 years. If you give leafy spurge flea beetles a decent chance, they'll work great!"

While ecologically based tools such as biological control are just one tool to controlling leafy spurge, Prosser pointed out.

"We want people to give biological control a chance, but we don't want them to ignore the other control tools that are available," he said.

"Herbicides are still the preferred tool for containing and preventing the spread of spurge infestations, for example, and sheep are an excellent mechanism for controlling spurge while diversifying cattle grazing operations. Biological control is just one of the tools that are available and can be used."

Prosser, Richard and Kirby encouraged people with questions about biological control to seek out the information that can help contribute to establishing a successful biocontrol site.

"If you have questions about biological control or Integrated Pest Management strategies for leafy spurge, give Dave Phillips, MSU Fergust County Extension Agent, a call at 538-3919 or email at acx...@montana.edu.

Also see:

Leafy Spurge: Biology, Ecology and Management