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Purging the spurge in Manitoba

Most farmers are well aware of leafy spurge. This invasive perennial plant was accidentally introduced to North America in the early 1800s. Today, according to the 2010 leafy spurge Economic Impact Assessment (www.leafyspurge.ca) this invasive plant costs the Manitoba economy over $40 million a year with over 1.2 million acres infested.

The Stanley Soil Management Association has been working hard to manage this invasive plant using biological controls, and they are seeing some fantastic results.

But first, why is leafy spurge such a problem plant? Part of what makes invasive plants so invasive is the fact that unlike native vegetation they lack natural predators. That means their growth goes unchecked while native plants are consumed by insects and livestock.

On top of this, leafy spurge reproduces at a rapid rate, producing hundreds of seeds per plant and sprouting new plants from its extensive root system. These roots are good at storing nutrients and that allows it to bounce back easily after experiencing harsh conditions. Leafy spurge forms dense stands and is not grazed by most livestock or wildlife. This plant is proficient at taking over a landscape and it needs to be controlled.

One way it can be controlled is through the use of insect biological controls. Biological control involves the intentional use of the invasive plant’s natural enemies to suppress its population. Insects from Europe, which feed only on leafy spurge, have been brought to Manitoba and are effective at weakening and limiting the spread of leafy spurge.

The most effective control agents in Manitoba have been multiple species of flea beetle (Aphthona). These little insects are capable of causing substantial damage to leafy spurge. The adults feed on the leaves during the spring and summer. In late August, the larvae emerge from their eggs and burrow below ground to feed on its roots. This stresses the plant and often infested plants won’t flower the year after larval infestation.

Stanley Soil Management Association (SSMA) has been using these flea beetles in the RM of Stanley since 1997. There have been over 200 release sites across the RM with 14 sites being monitored for effectiveness over the last five years. Overall, they have seen a 90 per cent reduction in the leafy spurge population with one patch being completely eliminated in a five-year period.

With the proper soil conditions, these biological controls can be effective but still take an effort to collect, release and monitor. It is important to take an integrated management approach when dealing with leafy spurge.

This means using the most appropriate and available chemical, physical and biological techniques in combination. And as always, prevention is vital. To limit the spread, make sure to check vehicles, livestock forage and seed stock for leafy spurge seeds and plants.

Report the presence of leafy spurge to the Invasive Species Council of Manitoba (www.invasivespeciesmanitoba.com).

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