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Invasive garlic mustard under fire in Minnesota

By John Myers / Duluth News Tribune

Garlic mustard may sound like a condiment at a sandwich shop, but it’s really one of the most noxious of the foreign invading plant species that have spread across Minnesota in recent years.

So far there are only two known outbreaks of the European invader in Duluth, both in eastern neighborhoods, and plant experts are asking for the public’s help in getting rid of them.

Volunteers are asked to meet Thursday from 5:30-6:30 p.m. at the corner of East 11th Street and Sixth Avenue East. Experts will explain how to identify garlic mustard and how best to get rid of it. A second effort at the same time is set for June 13, meeting at the corner of North Seventh Avenue East and Kelly Street above Skyline Parkway.

Experts caution that there may be more patches than they are aware of and say eradication efforts may take a lot of work over a long period, sometimes years of attacking the same patch.

“This is a long-term problem,” said Mark Tomshack, one of five unpaid invasive species management interns serving with the city of Duluth this summer. “Getting rid of even a single patch is a multi-year effort.”

The interns are working on multiple invasive species this summer, including buckthorn, bamboo and developing a long-term invasive species removal plans for the city.

Usually, garlic mustard flowers arrive in late April to early May, but with the unusually cool spring, Duluth’s patches have held off until June this year.

It’s one of the few troublesome invasive species that thrive in shaded areas.

Garlic mustard, which is spread by its seeds, usually is obvious as the only blooming white plant of its size in forested areas at this time. A plant that doesn’t grow fast until its second year, garlic mustard has single stems that are 12 to 36 inches high in its second year, when it flowers and produces hundreds of seeds per plant.

The plant can quickly dominate the forest floor, causing a dramatic decline of native plant cover within just a few years. That affects habitat for native insects, birds and mammals, according to the Minnesota Department of Natural Resources.

Management methods include hand removal, herbicide treatments and repeated burning, although little can be done to control large infestations. The best chance is to catch garlic mustard when infestations are small and plants or stems can be removed before seeds disperse.

“At first glance, one might mistake it for Creeping Charlie,” Tomshack said. Garlic mustard has small, round, scalloped-edged evergreen leaves in its first year. Second-year plants have larger, arrow-shaped leaves. The second-year plants also grow fast and produce a small, white, four-petaled flower. ”Other giveaways are that the leaves and stems will smell like onion or garlic when crushed, and when you gently pull up its root, it has a quirky bend to it.”

The DNR and the University of Minnesota have been testing how European insects might be used to kill garlic mustard. They’ve had good success, but so far federal regulators are prohibiting releasing the bugs in the wild.

“They say there are too many other species related to garlic mustard that might be affected. They don’t want to take the chance,” said Luke Skinner, deputy Parks and Trails director for the DNR. “It’s expensive to keep testing, so we need to decide whether to keep trying or give up on biological control.”

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