Saturday, May 31, 2014

Goodbye Wildflowers – Hello, Garlic Mustard

Garlic Mustard flowersEver since humans invented agriculture and started moving from continent to continent, they have taken plants with them. In most cases imported, non-native plants do not spread much beyond the bounds of horticulture. But the exceptions are increasingly worrisome to biologists. Removed from the pests and diseases that kept them in check in their natural habitats, some plants multiply explosively. They can smother native ecosystems in a matter of a few years.

Some of these invasive plants, such as bush honeysuckle, Japanese knotweed, phragmites reed, and purple loosestrife, are all too familiar in our region. As if that’s not enough, we must now add a new menace to the list. The latest member of this rogues’ gallery is garlic mustard, a pungent herb in the cabbage family.

Interestingly, garlic mustard has been in the United States for a long time. It was brought from Europe to Long Island in 1868 as a remedy for gangrene and ulcers. For a century, it spread relatively slowly, by an estimated 140 square miles a year. However, from the 1970s onward, garlic mustard’s rate of expansion skyrocketed to 2,500 square miles a year. Some biologists think it is no coincidence that white-tailed deer became increasingly numerous at the same time that garlic mustard took off. Deer avoid bitter garlic mustard but love to browse native herbaceous plants, conveniently clearing space for garlic mustard to take hold.

Unlike some invasive plants, garlic mustard has few growth limitations. Many invasives take hold primarily in disturbed soil (for example, a sunny roadside bank), but garlic mustard isn’t as picky. It likes any site in shade or partial sun, even fairly dry sites. It is particularly aggressive in rich, moist, forest understories, where it out-competes other herbaceous plants – and this is what has biologists particularly alarmed. These shaded woodland areas are the stronghold of most northern wildflowers, beloved species like trillium, spring beauty, bloodroot, and Jack-in-the-pulpit. Huge swaths of these plants are lost annually to garlic mustard advances.

Garlic MustardAnd the damage isn’t limited to wildflowers. Most native insects are adapted to eat only certain plants, so a loss of plants means a loss of insects as well. The importance of insects as food for songbirds and soil dwellers like salamanders cannot be overstated.

Unfortunately, there are no native insects that successfully eat garlic mustard. Although the rare West Virginia white butterfly, which uses toothwort as its natural host plant, will lay eggs on garlic mustard, the eggs either fail to hatch or the larvae don’t develop. In short, when this weed invades, insects, birds, and salamanders all lose ground.

The success of garlic mustard is amplified by chemical warfare. To ensure distastefulness, the leaves contain cyanide, insufficient to harm people but enough to knock down insects. Its roots exude compounds called glucosinolates that prevent other species’ seeds from germinating and kill beneficial soil fungi. Since native trees depend on root associations with fungi for growth, killing fungi enables garlic mustard to out-compete hardwood tree seedlings.

So what does garlic mustard look like? It takes on two appearances, depending on its age. In its first year it forms a ground-hugging rosette of green, kidney-shaped leaves, two and half to six inches across, with scalloped edges. Second-year rosettes rapidly produce a tall, central stem with leaves in an alternating pattern. The leaves on hairy stalks are triangular with toothed edges and are up to three and a half inches across. Young leaves emit a garlic odor when crushed. By May of its second year, garlic mustard is usually the tallest blooming forest plant (often waist high or more) with a terminal cluster of white flowers, each with four petals and six yellow stamens, four short ones and two long.

Each plant produces up to 8,000 seeds in long wiry capsules. The seeds look like miniature, dark, rice grains and they are flung up to ten feet when the ripe capsules explode. Most seeds germinate in the first two years and seedling densities of 24,000 per square yard have been reported. Some seeds remain dormant and can germinate up to ten years later.

While it’s easy to become discouraged learning about the challenges of this invasive, it’s worth noting that, in our region, garlic mustard has not reached the plague proportions of Midwestern states. We have time to control this menace. Control is labor intensive but simple. Identify patches of garlic mustard in your town. Pull them up in May before they set seed. Pulled plants can still ripen and disperse seed, so bag and send them to the landfill. And here’s the hardest part: Repeat yearly till the patch is gone.

Li Shen is an adjunct professor at the Dartmouth Medical School and the chair of the Thetford, Vermont, Conservation Commission. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation: wellborn@nhcf.org

Photos: Above, courtesy Wikimedia user Sannse; below courtesy Wikimedia user O. Pichard.


Guest Contributor

The Adirondack Almanack publishes occasional guest essays from Adirondack residents, visitors, and those with a biding interest in the Adirondack Park.

Submissions should be directed to Almanack editor John Warren at adkalmanack@gmail.com.




6 Responses

  1. Bill Joplin Bill Joplin says:

    This is the best article I’ve read about garlic mustard. I have been picking the %@#& stuff for about five years in a park and another open area near where I live in Newton, Mass. I spend part of almost every day doing this every May and June, and every year I have been able to extend my range. This is because of the plant’s two-year life cycle: you pick this year’s second-year plants and ignore the nondescript, low-lying first-year plants until next year when they will shoot up and make flowers and seeds. So after two springs of hard work in any given area, your work during the following springs won’t be bad — although seeds can lay dormant in the soil for up to seven years, I’m told. And since there are seeds in the dirt clinging to the roots of the plants you pick, try not to shake them as you move them to your bag. One other thing: If people don’t want to do more than pick them, lay them on, say, a trail, and keep on going, that’s actually quite helpful.

    • Laura S. says:

      Bill, read my comments below! If not sprayed the young triangular leaves & flower buds are quite tasty & nutritious. As I pull plants, I harvest those parts & compost the rest in black garbage bags left in the sun for two years to kill the seeds. This has given me a new perspective concerning them. I still pull any I see but feel a bit better knowing that they are edible & nutritious!

  2. Wally Elton Wally says:

    But don’t forget that if the plant is already flowering the seeds can still ripen and spread if the pulled plant is left lying on the ground.

    It is widespread in the Saratoga Springs area.

  3. Marisa Muratori says:

    Thank You….Once again ….very useful information…just saw some in my yard

  4. Ellen says:

    I’ve declared war on the garlic mustard in my yard, but it is tough. Last year I managed to remove it from one part of our property, only to discover a huge new patch of it in another part this year.

  5. Laura S. says:

    It was refreshing to read an article abt invasives that did not encourage using herbicides which are far more damaging than any invasives could be. many people do not realize that some invasives are edible & actually quite tasty & nutritious if harvested at the proper time. Two of note are Garlic Mustard & Japanese Knotweed. For Garlic Mustard, harvest the flower buds & upper triangular leaves. the lower rounded leaves tend to be bitter. They can either be sautéed or used in a mixed greens salad. One local restaurant utilized them as an appetizer by stuffing the leaves. For Japanese Knotweed, harvest the young shoots before the leaves unfurl & they can be used as a rhubarb or asparagus substitute. Be sure to only harvest from areas you know are not sprayed & pull the plant inc. the roots & dispose of the rest of the plant. I put them in black garbage bags & let them sit in the sun for two years & then utilize them as compost as the heat of the sun kills any seeds. This article has some good info & there are many other articles to be found online. Just make certain you gather them where toxic herbicides have not been used & dispose of the rest of the plant properly. http://eattheinvaders.org/category/onland/