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 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.

The plants were garlic mustard, widely distributed in the Old World. It was brought to our shores in the middle of the 19^th 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.