Garlic mustard is nearing the end of its flowering time around Chicago. Always an early bloomer, it came even earlier this El Ni–o year. There may not be a flower left by May 15. The leaves will soon die, but the dead stems topped with slender seedpods will remain through the summer. Each of those seedpods holds hundreds of tiny seeds ready to create the next generation of a weed that has become the latest scourge of natural areas in Illinois.

Garlic mustard (Alliaria petiolata) is a European species. Its original range extended from the arctic circle south to Italy and from England to western Russia. From that home range it has expanded to North Africa, India, Ceylon, and New Zealand as well as North America. It is a biennial. In the first year of its life it produces a low rosette of leaves. In the second year the flowering stalk arises, growing as tall as three feet in the best locations. The white flowers at the top of the stem have the four opposed petals of the family Cruciferae (the cross bearers). The leaves, sparsely scattered along the stem, are roughly triangular, with broad bases tapering to fine points. Their margins are irregularly toothed.

Garlic mustard likes light shade. You rarely encounter it in the deep shade of dense forests, and you are unlikely to find it in the full sun of prairies and meadows. The oak woodlands and savannas of Illinois supply the perfect conditions for garlic mustard. And since these communities are already weakened by a variety of stresses, they are ripe for conquest. Garlic mustard also flourishes along roadsides and on ground where some trees and shrubs are present. Wooded floodplains, where frequent disturbance from floods creates excellent conditions for invasion, can become garlic mustard beds where almost nothing else grows.

The first record of garlic mustard in the U.S. was on Long Island in 1868. (This information, and the material that follows on the history of garlic mustard, was taken from a report prepared for the Illinois Department of Conservation–now the Department of Natural Resources–in 1991 by Victoria Nuzzo of Native Landscapes, a consulting firm in Rockford.) It is now established in at least 23 states in the northeast and midwest and in adjacent areas in Canada.

The first official record in Illinois was a plant collected at Ravinia in 1918. This was the first time it had been found west of Ohio. The next time a plant was recorded in Illinois was in 1939 in Rockford. During the 1940s it was collected six times in four counties, including Du Page. Most habitat information mentions roadsides and waste areas–just the sort of location you might expect to find an opportunistic weed–but the plants were also showing up in parks.

In the 50s and 60s the spread continued. By the end of the 60s the weed was known to grow in 14 counties. The plant spread outward from a single point, but it also leapfrogged from one place to another, establishing satellite populations that eventually coalesced. The tiny seeds could easily be carried in a bit of mud clinging to a boot or stuck in the fender well of a car. Natural-area managers have noted that the plant is most likely to occur in portions of preserves that are heavily used by visitors. Where human visits are rare, the plant is seldom found. We are probably the main agents of dispersal.

Once garlic mustard gets a foothold, its ability to produce vast quantities of seed enables it to multiply rapidly. It added nine new counties to its range in the 70s and 12 more in the 80s. The plant spread south to Carbondale and began to move north into Wisconsin as well. By June 1991 garlic mustard had been recorded in 43 counties in Illinois and in the southernmost tier of counties in Wisconsin. A report from Funk’s Grove in McLean County characterized the plant as “abundant.”

The rate at which new populations were established approximately doubled every ten years. As of 1991, the weed was invading 7,000 square kilometers of new territory every year. Here in Cook County the days of spreading are over. The weed has occupied virtually all of the available habitat. Populations may grow or shrink on sites where the plant is established, but there are no new worlds to conquer.

The only safe and effective way to control garlic mustard is to pull the plants out of the ground. You can pull first- or second-year plants before they set seed. If they have not yet flowered you can just pull them and leave them lying on the ground. If they have flowered they might set seed even after they are pulled, so flowering plants are collected and taken to incinerators to be burned. We are not messing around here.

In the forest preserves garlic mustard is routinely removed from sites under active management. It takes lots of stoop labor, but if you stay at it year after year you can make a difference. Walk around a managed site and you will find only small, scattered populations. Inspect an unmanaged site and you will often find every square foot of suitable habitat occupied by garlic mustard.

Current rules governing land management in the Cook County preserves have greatly reduced the amount of garlic mustard removed, and on sites still under a moratorium forbidding all active management the weed is reinvading areas that had been cleared by years of hard labor.

Victoria Nuzzo cites theoretical work that states that 20 percent of a weed’s population must be removed annually for 20 years in order to eradicate it. And at least 15 percent of infested sites must be managed to produce an immediate reduction in numbers. Those numbers make the situation look hopeless. How could we remove 20 percent of Cook County’s millions of garlic mustard plants every year? The answer came to me in a flash of inspiration: we could eat them.

Like many members of the mustard family–mustards, cresses, and the diverse forms of brassica (cabbage, broccoli, cauliflower, et al)–garlic mustard is edible. The leaves, as the name suggests, have a pleasant garlic overtone. In a salad they fall somewhere between the sharp tang of arugula and the blandness of lettuce. Cooked, they could be treated like spinach. The current issue of “Natural Area Notes,” the newsletter of the Volunteer Stewardship Network, has an interesting recipe for black bass with burdock and garlic mustard.

There are five and a half million people in Cook County. Factor out the infants not yet on solid food and the people with unusual allergies, and there must be at least five million potential garlic mustard consumers in this county. A typical garlic mustard plant has only six to ten leaves, and they aren’t very big. We could each very easily consume ten garlic mustard plants at just one meal. If we all did this we would remove 50 million garlic mustard plants a year from the county. Even a plant as prolific as Alliaria petiolata could not long withstand an assault that heavy. I have a slogan for the project: Eat your enemy!

Now we come to the serious part of the program. Why should we care about garlic mustard? To the untutored eye a stand of garlic mustard in full and glorious bloom is a lovely sight. Why not just let nature take its course? Why this obsession with native plants and this hatred of everything foreign?

I would respond to the aesthetic argument by asking you to compare a patch of ground in a healthy woods with a patch of ground infested with garlic mustard. In a woods without garlic mustard the spring flower display might include large-flowered trillium, wood anemone, toothwort, bloodroot, trout lily, wild geranium, Dutchman’s-breeches, spring beauty, and wild ginger–among others. Where the garlic mustard flourishes you may have garlic mustard and nothing else.

The loss of biodiversity–the overwhelming variety that has characterized life on earth for more than a half billion years–is a major concern for conservationists these days. The invasion of garlic mustard into our woodlands is a striking example of what we are worried about. Replacing large numbers of local species with one cosmopolitan generalist impoverishes the earth. It places natural communities in peril and gives greater impetus to the alarming declines in numbers of species we see occurring all over the globe. Walking into an Illinois woodland and encountering dense growths of garlic mustard is like climbing into a cloud forest in Costa Rica and discovering house sparrows instead of resplendent quetzals.