Leafy spurge (Euphorbia esula) is a state-level noxious weed in South Dakota that can be found in nearly every corner of the state. Landowners are obligated to control noxious weeds, and the best strategy for weed control is an Integrated Pest Management (IPM) approach. Some of the most successful IPM programs for controlling leafy spurge rely heavily on biological control.
This article focuses on the use of biological control for leafy spurge management. However, The SD Department of Agriculture recommends spraying or mowing the perimeters of spurge patches if necessary during the establishment phase of biological control (see below). It is also recommended that neighbors cooperate on an IPM program for noxious weed control to reduce unnecessary input expenses and to improve the chances for successful biocontrol. For more information on leafy spurge control or other noxious weeds, visit the SD Department of Ag website or view SDSU Extension’s 2016 Noxious Weed Control Guide.
Figure 1. South Dakota leafy spurge distribution 2015.
Figure courtesy of the SDDA.
General Facts About Leafy Spurge
- Leafy spurge is a non-native species of Eurasian origin.
- Leafy spurge is a perennial, long-lived plant.
- Leafy spurge can grow in many soil conditions and can mature as a short stature plant on dry hill sides or as a robust plant up to 3 feet tall in more favorable areas.
- Leafy spurge can reproduce both by roots and seeds. Roots contain pink buds that can produce new roots and shoots. The plant also has a unique ability to ‘shoot’ seeds up to 15 feet when its dry seed capsules explode. Seeds are viable in the soil for several years.
- Leafy spurge can be identified by its green clustered stems, yellowish-green flowers, and alternate leaves. Leafy spurge has a milky white juice found throughout the plant.
More information on leafy spurge can be found in the USDA’s Plant Guide for Leafy Spurge.
Leafy Spurge Biological Control
The benefits of utilizing biological control in an IPM system for leafy spurge are clear. Successful biological control can dramatically reduce populations and input costs in labor and chemicals while retaining pasture plant community diversity by reducing or eliminating non-target chemical impacts to desirable native broadleaf plants such as native flowers and legumes. Labor and monetary savings can then be invested into overall pasture management, including managing the biocontrol program by annually moving biocontrol agents into the pasture.
By far, the most successful biocontrol agents for leafy spurge in South Dakota have been the leafy spurge flea beetles (Apthona spp.). Over the last 20 years, many State, Federal, and private organizations have worked closely with landowners to collect and distribute flea beetles for leafy spurge control and to establish a series of ‘insectories’ on private and public lands for future collection and redistribution.
Flea beetles control leafy spurge through foraging on the roots as larva and through foraging on the host plant as adults. Flea beetles are generally collected by hand via simple sweep nets in late spring and early summer prior to the female beetles laying eggs in order to have females lay eggs at the new release site to build a new population.
Figure 2. Leafy spurge flea beetle (Apthona spp.). Photo courtesy of USDA.
Establishing a Successful Leafy Spurge Biological Control Program
Biocontrol is a proven method of managing spurge populations. However, not all biocontrol programs meet with immediate success, and in certain cases biocontrol with flea beetles simply will not work. Biocontrol requires that the spurge beetles have a population of spurge to feed on, thus the beetles will never completely eliminate spurge in the pasture. Rather, biocontrol is aimed at reducing the leafy spurge population to an acceptable level. It can take as little as 1 year or as many as 6 years for a released population to firmly establish and significantly impact the spurge, with 3 to 5 years being common.
How can Landowners Participate in Leafy Spurge Biological Control?
Today, the South Dakota Department of Ag in partnership with County Weed Supervisors coordinate the majority of public collection and redistribution of leafy spurge flea beetles. Landowners can call the South Dakota Department of Agriculture 605.773.3796 or their local county Weed Supervisor to be placed on a contact list.
In most cases, landowners who actively participate in a collection day will receive a few packages of beetles for release, depending on how well the collection goes. Each landowner who attends a collection will participate in sweeping and/or sorting and packaging beetles. Generally collection days require about 2 – 4 hours of time investment. Participating landowners should bring a cooler with cold ‘blue’ ice that can be purchased at any store where camping supplies are sold. Landowners will be sent home with instructions for handling and release of the beetles.
Managing Beetles During and After Release
There are two basic strategies to releasing flea beetles in leafy spurge. The first relies on distributing fewer beetles over several patches in a pasture, typically a few thousand beetles at each site. This strategy works well if there are many smaller scattered patches over a larger area. The second relies on releasing tens of thousands in a single release area or within 1 large patch. This strategy works well if spurge is fairly contiguous over large areas and if the desire is to create a collectable population quickly for redistribution. The risk here revolves around the susceptibility of the entire release population to a single catastrophic event such as a hailstorm or a chemical overspray that kills the spurge patch or the beetles directly. In any event, sweeping and moving your own beetles in subsequent years is necessary for long-term success. This can be a very rewarding experience and is generally an enjoyable way to spend a day out in the pastures!!
Characteristics of a Successful Release
- Adequate spurge of various stages of maturity but not overly dense. Sites easy to walk through are a good benchmark
- Open exposure, not shaded.
- At least an acre or two of fairly contiguous spurge
- Generally well drained soils, but not sandy. Sandy soils have generally proven to be a hindrance to population establishment.
- Once established, beetles will move into less favorable habitats such as thick or shaded spurge patches. Movement can be dramatically enhanced through active collection and re-distribution in subsequent years.
Spurge Flea Beetle Biocontrol:
Guide to Successes & Failures
There is no way to know for certain whether your release will be successful. However, the chart below provides information from several sources in South Dakota where successes and failures have been predictable and repeatable. The first step to a successful biocontrol program is to reach out to neighbors and agency staff who have participated in biocontrol programs in your area. Ask about such factors as soils, slopes, and general information that can guide you to a successful release.
|Action or Event||Best Case Scenario||What to Avoid|
|Release||Larger patches, moderate density patches, full sun exposure, well drained, ‘heavier’ soils||Very dense or very sparse patches, shade, sandy, overly wet|
|Redistributing beetles annually||Look for larger patches. Sweep until an adequate number of beetles in net and re-release immediately into target patch. Package and cool only if necessary.||Do not redistribute into areas listed above.|
|When to collect/redistribute||Warm, sunny, low wind days in from about mid-June to early July||Do not collect after about the second week in July as most females will have already laid eggs.|
|Grazing||Avoid grazing new release sites in the first year during June and July if possible.||Heavy grazing, compaction in any area where beetles are present|
|Winter||Residual vegetation structure adequate to capture snow and insulate soil (good grazing practices!!!)||An open winter with little snow and little residual vegetation cover can allow frost depths to penetrate deeper, possibly killing larva in the roots.|