Conservationists want to kill off garlic mustard

Tuesday, February 3, 2009

Garlic mustard is threatening native plant species in Ontario woodlots and fence rows, even the mighty oak, and the Nature Conservancy of Canada recommends spraying it with Roundup and killing it.

Conservation groups usually want chemical pesticides banned, so what's with the Nature Conservancy?

It's not the only conservation group to suggest this, says the Conservancy's science and stewardship co-ordinator Mhairi McFarlane, based in London, and garlic mustard is indeed that bad. Using Roundup "is the least damaging way to kill it off, believe or not," she says.

Some attempts to remove garlic mustard may actually help spread it. For example, disturbing earth by uprooting it tends to bring seeds to the surface, where they germinate.   

Uprooting is a five- to 10-year project best done in a garden setting "or you will never get rid of it," McFarlane says. Clipping flowers at the right time can prevent seed set, but must also be repeated. And clipping at the wrong time can spread the seeds.

Garlic mustard stays green and active in low temperatures, when native plants are dormant. Spraying directly on the plant is best done in winter months. There should be no snow, McFarlane says, and temperatures should be above freezing. Stream banks should be avoided, she says, because of scientific evidence that Roundup affects water fauna. Garlic mustard doesn't just crowd out native species, it poisons them. Chemicals in the ground surrounding the plants prevent normal plant growth. "Acorns won't germinate if they fall in a garlic mustard patch," McFarlane says.

A single plant produces many tiny black seeds which are easily carried on shoes, in pant cuffs, and even in the treads of vehicles.

If an all-terrain vehicle drives through a garlic mustard patch with ripe seeds, there will typically be a trail of garlic mustard plants along the path the vehicle took, McFarlane says. BF