Garlic mustard ‘diabolical’ invasive plant

A man in a county park is removing tall plants with small white blossoms in a wooded area. A couple is extracting that species from a county roadside. A group of people is doing the same thing at the Touch the Earth Natural Area. The target of all this effort is called garlic mustard, Alliaria petiolata, a member of the mustard Family with leaves that smell and taste like garlic.

It was brought from Europe and first documented on Long Island, New York, in 1868. Since then, it has rapidly spread across most of the eastern United States and Pacific Northwest. It has become one of our worst invasive alien herbs, being the only one that can dominate a forest floor.

What is so scary about garlic mustard? I have found patches of it along just about every county road I’ve been on. Those patches at the edge of a woods are the biggest problem. Because of its numerous competitive advantages, in a decade or so it can dominate the nearest part of the woods and continue spreading. That means the native woodland wildflowers are overcome by this invader, which steals their sunlight, water, nutrients and space.

At its worst, a forest floor that formerly displayed a glorious array of native red, yellow, blue and white blossoms for months will be a sea of white flower clusters for a few weeks. If that doesn’t sound bad enough, think of this: because garlic mustard is ignored by most woodland critters that depend on native leaves, pollen, nectar, fruits, seeds and roots, they must find their food elsewhere or perish. The same goes for the carnivores that feed on these herbivores. Garlic mustard fights biodiversity. Diabolical.

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Years ago, my wife and I were at Mill Race Park and discovered garlic mustard in the process of choking out a big beautiful patch of native Virginia Bluebells, so I contacted the Columbus Parks and Recreation Department and educated them on this threat. Between Sierra Club’s pulling and the parks department’s mowing, it was brought under control.

As an obligate biennial, garlic mustard must bloom its second season no matter how small it is. In its first season, it is a low cluster of roundish leaves with toothed edges. These leaves remain green over the winter. In April of its second season, the plant bolts, producing a stem that is as much as 3 feet tall when blooming and has narrow heart-shaped foliage. The blossoms are about a half-inch wide, have four white petals arranged in a cross-shape and are located in clusters at the top of the stalk. The fruits are slender pods about 1 to 3 inches long. One plant produces hundreds or even thousands of seeds. If in doubt, crush a leaf. If it smells of garlic, you’ve identified garlic mustard.

Since it only reproduces by seed, the key to eradicating garlic mustard is to prevent seed production. Eliminate it by cutting the stalk 2 inches or less above the ground, or spraying with herbicide when native plants are dormant, or by pulling. When pulling, grab it low and pull it slow. Root fragments can resprout, so try to get all of the taproot. Cut or pulled blooming or fruiting plants should be placed in trash bags, baked in the sun for a week, and then placed in a landfill.

Few people have heard of garlic mustard, and fewer know much about it. Land owners should constantly be on the lookout for all invasive plants. This is the “new normal.” Removing a few plants this year is easier than eliminating hundreds in a few years.

Doug Johnson, a student of nature for 50 years and a Bartholomew County resident, occasionally leads nature strolls. He and wife Casey care for 23 natural acres. Send comments to [email protected].