Leafy spurge biocontrol season is here
The cool wet spring has impacted just about everything, including growth of desirable and undesirable pasture plants like leafy spurge. Leafy spurge (Euphorbia esula) is a noxious weed in South Dakota that can be found in nearly every corner of the state. Landowners are obligated to control their noxious weeds, and the best approach to 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 using spurge beetles (Apthona spp.).
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 leafy spurge populations and input costs in labor and chemicals while retaining pasture plant community diversity by reducing or eliminating non-target impacts to desirable native broadleaf plants such as native flowers and legumes. Labor and monetary savings can then be applied toward a greater investment into overall pasture management, including managing the biocontrol program by annually moving spurge beetles in the pasture.
The most successful biological control agents for leafy spurge in South Dakota have been the leafy spurge flea beetles (Apthona spp.). 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, ensuring eggs will be laid at the new release site to build a new population.
Acquire the bugs now
The South Dakota Department of Ag in partnership with the county weed agents coordinate the majority of public collection and redistribution of leafy spurge flea beetles. Landowners should call the SD Dept. of Ag at 605-773-3796 or their local county Weed Supervisor to be placed on a contact list.
Landowners must actively participate in a collection day to receive beetles for release. Each landowner who attends a collection day will participate by sweeping and/or sorting and packaging beetles. Generally collection days require about 2 – 4 hours of time investment.
What to bring to a collection day
1. Participating landowners should bring cooler with cold ‘blue’ ice that can be found at any store where camping supplies are sold. Landowners will be sent home with instructions for handling and releasing the beetles into proper spurge beetle nurseries.
2. Sweep nets if you have one. Generally, extra nets are available at collection days to borrow.
3. Something cool to drink
4. Bug repellant
Managing your own leafy spurge program can be simple?
There is no way to know for certain whether your release will be successful. However, in South Dakota we’ve found that 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.
Things to consider when releasing beetles
1. Adequate spurge of various stages of maturity but not overly dense. Sites easy to walk through are a good benchmark
2. Open exposure, not shaded.
3. At least an acre or two of fairly contiguous spurge.
4. Generally well drained soils, but not sandy. Sandy soils have generally proven to be a hindrance to population establishment.
5. Avoid heavily grazed sites
6. Once established, beetles will move into less favorable habitats such as thick or shaded spurge patches.
Too many people have become convinced that they need to attend a collection day to get bugs. The other alternative is to spend a sunny afternoon on your place or your neighbors place sweeping and moving bugs around with a ATV (or even a horse for those hard to reach areas). Simply sweep for a half hour or so, drive to a nearby patch, and gently release. As long as the bugs don’t get to hot, the will be fine. If everyone spent a bit of time moving their bugs, it would all but assure that we’ll have strong populations in the future.
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. Consequently, the beetles will never completely eliminate spurge, but rather reduce the 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 3 to 5 years is common.
While this article focuses on the use of biological control, landowners must take steps to ensure that noxious weeds do not spread on their property or that of neighbors. The SD Department of Agriculture recommends spraying or mowing the perimeters of spurge patches if necessary during the establishment phase of biological control. 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 control. Contrary to belief, herbicide that is used for leafy spurge control does not kill the leafy spurge beetles. It does kill their food, which is the only way the beetles survive. For more information on leafy spurge control or other noxious weeds, visit the SD Department of Ag website or SDSU Extension.