When the ditches are full of purple loosestrife, in bloom during July and August, it is a treat to drive along the highways. It is happily a common sight since the seeds are carried far and wide by the ditch waters. --Katherine McKenzie, Wildflowers of the Midwest
Although McKenzie doesn't describe herself as either an artist or a botanist, this 20-year-old volume is full of delicate watercolors and graceful descriptions. But since she wrote these words, Lythrum salicaria has transformed from roadside decoration to wetland plague.
"If we could only have got a handle on it earlier," said Larry Hodak, site steward for the prairie restoration at Sauganash Prairie Grove, part of the LaBagh Woods Forest Preserve at Bryn Mawr and the Chicago River. Hodak kind of crumples at the sight before us; a solid acre of purple plumes. Here and there scouting columns of the weed have advanced into the wet prairie and savanna. From these advance initiatives the hardy perennial will establish long-lived colonies, gnarled clumps that will produce an average 2.5 million tiny seeds apiece per year.
The purple loosestrife monoculture shares the edges of the marsh it dominates with red bulrush and half a dozen other native species of sedge. But first-year volunteers sprout in the wet prairie among the sneezeweed and gerardia, saw-toothed sunflower and sweet black-eyed Susan, blue flag iris, monkeyflower, American bellflower, and the native winged loosestrife, Lythrum alatum. Without intervention, purple loosestrife will drive them all out within a few years, replacing the community with a monocultural ghetto.
What makes loosestrife such a successful competitor? Two factors are mainly responsible according to a 1987 publication of the U.S. Fish and Wildlife Service, Spread, Impact and Control of Purple Loosestrife in North American Wetlands.
First, purple loosestrife has no natural predators here, having escaped the insects that feed on it when it emigrated from its homelands in Europe and Asia. The tiny seed may have stuck to the hooves of pigs and cattle, the wool of sheep, or the hay used to feed these animals onboard; seed may have contaminated the rock and sand loaded aboard ships as ballast, then dumped on New World shores to make room for lumber, cotton, and tobacco. Loosestrife found freedom here, and was even cultivated as a medicinal plant.
Second, purple loosestrife is an opportunist, thriving on disturbance. Ecosystems generally make room for strangers grudgingly, granting a place on the bench only after a prolonged period of sniffing out and snubbing. But in the free-for-all after a Caterpillar tractor tears up the land, the first is made last, and the last is made first. A whole different set of characteristics marks the successful competitor then. Instead of conservative species that have developed a symbiosis with other residents, generalists take over: fast-moving, fast-talking, fecund types that don't have time to waste visiting with the neighbors.
Although any correlation is unproven, purple loosestrife shares its exponential rate of growth across the land with the spread of McDonald's. Both are now in the asymptotic phase: the rate of reproduction is streaking toward infinity, at some apocalyptic point just up the road. Both forms are crowd pleasers, killing off local variety using proven but undifferentiated means. And both spread along the ditches flanking our national highway system, that dubious repository of national wealth that mixes and mashes national culture into a tasteless gruel. Just as we have abandoned the room-and-board surprises of the back road and village for the superhighway and fast-food cloverleaf, regional diversity in wetland plant communities is giving way to monolithic stands of purple loosestrife.
Roadside ditches could be ceded to the weed except that the stringing arterioles of purple loosestrife have propagated across the land: from roadside ditches Lythrum salicaria has spread to stressed-out wetlands, fishing lakes, and prairie potholes. An alien species, an unfettered opportunist, is particularly noxious when it encounters a highly stressed and disturbed ecosystem.
The threat to diversity is obvious when an invasive alien plant, or a shopping mall, extinguishes some tiny, threatened forb. But it's also true that every time some event reduces the population of an indigenous plant or animal, it shrinks that species' ability to respond to change: to survive. All organisms are bequeathed a genotype richness, a consequence of their own unique evolution, that's not always expressed in any one individual but held in reserve. The ability to respond to stresses is limited by evolutionary potential, and when populations are reduced, the genetic horizons are narrowed. For species survival Noah's ark strategies just won't work.
Hodak provided a list of over 200 native species from Sauganash Prairie Grove, an in-progress census of the neighborhood. Walking the prairie with him is like going to his block party: he'll introduce you to scores of savanna plants, the tiny, unassuming pussytoes and prairie sundrops, odd-looking rattlesnake master and green dragon, and stunning Michigan lily, marsh blazing star, and Indian grass. "I'm not that good with the sedges," he says, referring to the modest but kaleidoscopically inventive grasslike plant. Nine are listed. But you can find more than 15 on the site if you're willing to search for and identify them.
The purple loosestrife stand is stark and barren, however, with only a few blades of redtop grass and pussy willows fighting back. "They sure are pretty, though," my sister says, submerged in the head-high fields of purple blossoms. "The polio virus is pretty, too, in its own crystalline, polyhedral way," I say. "That's ridiculous," she says. "You go too far."
There is broad agreement, however, among agriculturalists and natural land workers that, pretty or not, purple loosestrife has to be controlled. It not only kills off plant communities but, by replacing indigenous cattail and other reeds and rushes, destroys nesting habitat and forage grounds for canvasback ducks and long-billed marsh wrens, black terns and muskrats, minks and bog turtles.
Until recently no satisfactory control mechanism could be found. Fire, that miraculous culler of invasive prairie brush, doesn't do well in wetlands. And anyway purple loosestrife seemed impervious to it. Chemical methods that became available in the early 70s with the advent of glycophosphate-based broad-range herbicides, sold under the trade names Round-up and Rodeo, are widely used today. These systemic poisons are reportedly short-lived, with a half-life of two months, but they're properly used only on scattered sprouts, with direct application to the leaves at close range. And many land workers are troubled by the possible ramifications of their use on the ecosystem.
The favored strategy for controlling purple loosestrife has focused on reducing disturbance stresses on wetlands, which allow loosestrife seedlings to spring up from dormant seed stocks, and responding quickly to new colonizations. But the vegetative management guidelines put out by the Illinois Nature Preserves Commission warn: "The chances of success are best with the smallest infestations. Early diagnosis is critical." They advise that the habitat be scoured for the first signs of invasion, and that individual plants be pulled out with the roots intact and removed from the site in plastic bags so that seeds aren't dropped.
Today biologic controls are the best hope for success against purple loosestrife: bringing in the enemy's enemy. In the mid-80s a research team scoured western and central Europe for loosestrife-eating bugs. Out of the 120 plant-eating insects they found munching on L. salicaria, 6 were recommended for detailed ecological and host-specificity studies: a cecidomyiid fly whose galling of the plants can reduce purple-loosestrife foliage by 75 percent and seed production by 80 percent, a stem- and root-boring weevil, two chrysomelids (beetles), and two weevils that mine ovaries and seeds.
After studies were made and cautionary tests performed and researchers were confident that no new Frankensteins would be released on the continent, three finalists were approved, the two closely related beetles and the root-boring weevil. They were checked for parasites and reared in large numbers in the laboratory, and in the summer of 1992 released in various combinations at wetland sites in New York, Maryland, Pennsylvania, Virginia, Minnesota, Oregon, and Washington state.
The results have been mixed and modest thus far. In Minnesota the first-year site was unceremoniously flooded by the Mississippi River, and the whole experiment was up for grabs. But some of the beetles survived and reproduced. In fact, all the insects wintered successfully in all the states where they were introduced: they paired up, mated, and laid eggs on the purple loosestrife. In Oregon, in the experiment's third year, one site experienced an explosion of beetle growth and activity, and purple loosestrife plants were eaten down to the nub.
Biologists on the project are hopeful but advise patience as the insects work themselves into their new communities. Control may be some years down the road. But based on positive signs, new combinations of the insects were released in 1993-'94. Seven locations in Illinois were selected for release of the beetle pair, including a Cook County site at Powderhorn Lake, Waukonda and Brandenburg bogs in Lake County, several sites in the Fox Valley, and one along the Mississippi in Carroll County. Typically a netting tent is constructed over an area of purple loosestrife infestation and a thousand or so of the insects are shaken onto the plants, where they seek mates and meals and lay eggs. Two weeks later the netting is removed, and the biologists wait and see what happens.
They are waiting still. Although the beetles left signs of foraging activity, they've disappeared. With good luck, that's because they've survived but gone into summer dormancy and incubation.
According to the U.S. Fish and Wildlife publication, the goal of biologic control is not eradicating the alien but reducing its presence to an acceptable level. This goal represents not only a nod to reality but a welcome search for balance, a rejection of dominance and monoculture. Rather than annihilating their host, the beetles and weevils are predicted to reduce purple loosestrife populations by 90 percent.
It's hard to tell the story of purple loosestrife, its immigration and spread, its glamorous success and the scramble to control it, without drawing a few parallels to our human legacy. "The extent of habitat disturbance," the U.S. Fish and Wildlife publication states, "has been and continues to be parallel to the exponential increase of our human population." Is there a big research lab somewhere in the universe searching for a control organism to limit the relentless growth of that most aggressive, invasive alien--us? Or will we find a limit and balance on our own?