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Full-Spectrum Warfare

Getting rid of the estimated 340,000 acres of leafy spurge in Manitoba, which costs ranchers and municipalities an estimated $19 million a year in control efforts and lost grazing, requires full-spectrum warfare.

That’s because the Eurasian invader, with a root system up to 26 feet deep and 15 feet across, can recover quickly from anything, including spraying, and repeated tillage or mowing. Each plant produces up to 140 seeds per stem which remain viable for up to eight years in the soil. In hot, dry weather, pods literally explode, scattering seeds up to 15 feet away.

Spraying can knock out small patches of the weed, but for larger patches, herbicide application must be well timed and used repeatedly to ensure control.

It doesn’t, however, kill the seeds, so it is important to scout early and nail spurge patches before they can get established. Non-selective herbicides such as Amitrol 240 is good for one season of control, but since it kills everything, the reduced competition could make it easier for leftover seed to spring up. Dicamba (Banvel II) offers similar results.

Two applications of 2,4-D amine in spring and fall can suppress the weed over time. Tordon 22K (Picloram) can kill 90 per cent of the spurge the first year. It leaves a residue that is effective for up to five years, but in sandier soils, it can leach into groundwater and has been detected in wells after years of repeated use. MCPA works in crops, but is not registered for pastures or rangelands.

Mowing every two to four weeks to prevent flowering can help.

Repeated cultivation every two or three weeks at a four-inch depth from early spring until fall can suppress spurge, but using this tactic on small patches can cause root fragments to spread, and buds along the roots may sprout and create new seedlings.

Hand picking in early spring can help. All leafy spurge plants and roots should be burned.

Multi-species grazing with sheep or goats has been shown to work, but may take years to eradicate large populations. Source: Leafy Spurge Stakeholders Group

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