Category: Plants

Why do weed warriors love to hate the garlic mustard?

The garlic mustard: From potherb
to invasive species of choice.

This is the time of year when weed warriors armed with shovels and pruning shears do battle with that subset of the plant kingdom called Invasive Plants. They march into woods and fields, fearless in confronting any leafed alien that poses a threat to our native plants. They emerge at the end of the day exhausted from their pulling and hacking, often with arms bearing badges of honor in the form of nasty scratches and cuts.

Clearly not all weed warriors fit this heroic mold. There are many others—perhaps the majority—who also believe fervently in the crusade against alien plants, but not so much in hard physical labor. They opt to express their beliefs in symbolic acts, a little like casual church-goers or Earth Day marchers.

A devil’s nursery. I recently came across what seemed like an illustration of this idea at a place near the Potomac River called Hughes Hollow. It’s a kind of “natural” area, favored by birders, where a system of canals and sluice gates control the water level of two artificial ponds covered with lily pads.

A dirt road runs across a dike at Hughes
Hollow, an unnatural area brimming
with life, both native and exotic.

A dirt service road separates the two ponds. Alongside grows a tangle of plants, nearly all of them non-native species. For a weed warrior, I’d imagine it’s like walking down the aisle of a devil’s garden nursery.

As for myself, I admired the exuberance—if not the purity—of this plant profusion. Bumble bees buzzed past my head as a yellowthroat warbler went “witchety-witchety-witchety” in a stand of willows.

A modest experiment. I walked along for a short distance, and then I came upon something curious. It was a neatly laid out stack of withering plants, followed by another, then another.

A withering bunch of garlic mustard
lies on a bed of more fortunate invasives.

The plants were garlic mustard, widely distributed in the Old World. It was brought to our shores in the middle of the 19th century to perk up the salad bowl and vegetable pot with its garlicky flavor.

Out of all of these invasive species it appeared that the weed warrior only pulled out garlic mustard. I found no sign that any of the other invasive plants along the roadway had received similar treatment. Why ?

I had a suspicion, but I needed to confirm it by performing an experiment. My method of analysis would be straightforward, requiring no replication, peer review, or even any actual data. I would simply walk down this service role and pull on every plant I encountered. I set off on my botanical adventure.

Death to dandelions! I first approached a dandelion. I admired the fierce yellow of its blooms, rivaling the sun itself. Italian immigrants once used its bitter leaves in salads. I knelt down and hooked my forefinger around the plant’s stem, right at ground level, and gave it a yank. All I came up with was a rosette of leaves oozing white sap from their base.

My next intended victim was vetch, a plant of slender vines, purple flowers, and delicate compound leaves. The nodules on its roots contain bacteria that convert nitrogen from the air into a form usable to other plants. Again I knelt down. With my fingers I traced the plant’s sinewy stem through the neighboring plants until I found where it entered the ground. This time I pulled more gently. But the results were the same.

Equal-opportunity invasive. I tried uprooting one non-native plant after the other. Some were tiny and delicate. Others were thorny and prickly. In all cases, try as I might, their roots refused to give up their hold on soil from which they sprang.

With one exception. As you have already guessed, it was the garlic mustard. I found a small patch that the weed warrior had evidently missed when he passed through earlier.

Their stems were tall and easy to spot and substantial enough that I could get a firm grip on them. I didn’t even have to kneel down to do so. I pulled, and as I knew would happen, out they came, roots and all. It was almost like these latter day pot herbs welcomed their demise.

I lay my first bunch down on the side of the roadway. I pulled up several more and lay them over the others, noting how naturally they seemed to nestle into a state of repose, like cordwood or neckties in a bargain bin.

This was all the proof I needed. Weed warriors love to pull out garlic mustard because, well, it’s easy to pull out. Science doesn’t always have to be complicated.

I don’t like purple deadnettles. It might be my age.

From their blockhouses along the Potomac River bluffs the Union soldiers keep a lookout for any movements of Confederate troops across the river in Virginia. It is 1862, a time of conflict.

I set off down the trail.
My horse remains at home.

Another conflict of sorts continues along these same bluffs, now part of the 639-acre Blockhouse Point Conservation Park on River Road. Today’s combatants are not opposing armies, but plants. Facing off on one side are the trees, shrubs, and wildflowers that are native to this area. On the other side are plant species that came from someplace else: the invasives.

If the invasives gain the upper hand, as they have in many places, they could wipe out the natives. Here in Montgomery County and around the country, people have organized to prevent this from happening.

Alien invaders. Among them is Carole Bergmann, forest ecologist with the Montgomery County Department of Parks. Passionate about her mission, she has founded the Weed Warriors, a group dedicated to uprooting and hacking down these alien invaders.

Bergmann urged me to visit Blockhouse Point as an example of a “really high quality contiguous forest,” still relatively unscathed by change. But keep your eyes open, she advised. For even here, the invasives are at work.

I parked at the little lot on River Road and headed down towards the river on a well-groomed trail. I admired the soaring beeches, oaks, and tulip poplars.

The orange-red sap of the
fragile bloodroot contains
chemicals that might help
fight bacteria and reduce

As Bergmann promised, these are beautiful woods with remarkable plants, each with a story.

My first find was a pair of bloodroot, their leaves still curled around their stems, their delicate flowers poised to open. Native Americans used this plant’s orange-red sap as a dye. Today, the plant is on the U.S. Food and Drug Administration’s list of fake cancer cures.

The trail skirted a swampy area with a stand of skunk cabbage, named for the pungent odor its leaves release when crushed. In the dead of winter, this extraordinary plant produces heat that enables it to push up through cold mud and snow. Well before other flowers open, the skunk cabbage’s hooded blooms are already attracting pollinating insects with their warmth and odor.

On a sun-bathed hillside I found a carpet of wildflowers called spring beauties. You

The skunk cabbage beats
the competition for pollinators
by flowering in the winter.

would never guess from looking at their delicate pink-veined blossoms that their roots form into grape-sized tubers. These are perfectly edible if you don’t object to the taste of dirt.

Honeysuckle taking hold. But here the plot thickens. Among the spring beauties I found snippets of dark-leaved vines poked up among the shy flowers. It was honeysuckle, introduced to the U.S. from eastern Asia. An aggressive tree climber, its dense foliage shades out the native plants living below.

Now I stood on a bluff overlooking the canal and river. Around me a multitude of tiny flowering plants poked up between fallen leaves. Among them the purple deadnettle, a

What looks like the leaves
of this spring beauty
actually belong to an
invasive honeysuckle vine.

Eurasian native that equally thrives along roadsides among the broken glass and cigarette butts.

I slid down the bluff to the floodplain along the canal. Japanese barberry, with its familiar scarlet fruits, pricked my legs. I forced my way through tangles of multiflora rose, also from east Asia, their sharp thorns grasping at my shirt and puncturing my arms and hands and leaving them covered with drips of blood.

As Bergmann explained it, the land along the canal, altered and flooded with sunlight, creates an ideal corridor for invasives. For this reason, she adamantly opposes any proliferation of trails through the park. Her nightmare scenario would be a full-scale assault by Vietnamese stiltgrass. “If we don’t control it,” she said, “stiltgrass will shoot up and down all the trails, even in shade.”

Contrarian on aliens. My walk had come to an end, and now my mind wandered to another setting with invasives—but with subversives as well.

Earlier this year I attended a seminar on non-native species at the annual meeting of the American Association for the Advancement of Science, in Washington, D.C. There I met Mark Davis, a plant ecologist, author of the book Invasion Biology, and professor at Minnesota’s Macalester College.

According to Davis, the invasives issue is less about plants and animals, and more about us—our personal likes and dislikes.

Speaking of aliens, this one
below the Blockhouse Point
bluffs looks straight out
of War of the Worlds.

“When we refer to a healthy ecosystem,” he said, “we’re talking about how we want the ecosystem to be.” Invasive species do affect ecosystems; that’s scientific fact. Some of the changes we like and others we don’t; that has nothing to do with science.

The most vehemently anti-invasive views are typically held by people in their 50s and 60s, he maintains. “Kids growing up today are surrounded by people and cultures from all over,” he continued. In the future, Davis predicts, we will focus less on managing non-native species and more on changing our attitudes towards them.

That said, Davis supports taking firm action when species threaten our health or our economy—alien or native. The emerald ash borer, which is devastating ash trees throughout North America, originally comes from Asia. But the mountain pine beetle, which is wreaking havoc with pine trees across the western states, is 100 percent American.

Back at Blockhouse Point I looked out at the river. The creatures living in its waters tell even more topsy-turvy stories of biology and beliefs. These stories will remain to be told.