The Mark of Cane
An insect the size of a pepper flake could accelerate coastal erosion.
The tiny insects have been described as time bombs. One biologist said recently that their damage could precipitate the disintegration of the entire lower delta of the Mississippi River. The state of Louisiana is already engaged in a 100-billion-dollar struggle with nature to slow the pace of coastal land loss, and scientists now have reason to worry that an insect the size of a pepper flake could accelerate the erosion to untenable levels. The bugs only appear to attack one kind of plant, the roseau cane, but that plant is foundational to the wetlands of lower Plaquemines Parish. The Louisiana Department of Agriculture and Forestry has imposed an emergency quarantine on the movement of the plant, and various government agencies at the state and federal level are sending more than two million dollars to researchers to study the die-off and its potential solutions.
At this point, there are few, if any, concrete solutions to the problem. In Eastern China, where the scale insect is native, the solution for an outbreak of the bug is to burn the affected cane to the ground and let the plants start over. But Louisiana is criss-crossed by 50,000 miles of pipelines, which carry oil, gas, and other explosive materials that make controlled burns impossible in the marshes.
For now, thanks to the influx of funding, researchers are hustling to get a better grasp on all of the factors at play. Very little is known about the scale insect, even in its native ranges in China and Japan, where its damage doesn’t come close to the scale of destruction in the Lower Delta. But scientifically, even the roseau cane, which is not to find in Louisiana’s wetlands and one of the most widespread plants on Earth, still has its own mysteries. The reed has a complicated history in the state, and there are still unanswered questions about the tall, bushy, ubiquitous plant—most notably its mysterious arrival to the Mississippi River’s birdsfoot delta in the first place.
Ferocious urge to expand
At first sight, the roseau cane research garden where I met Jim Cronin looks unremarkable and perhaps like something that has grown by accident. Rows of bulging plastic pots stand alone in a grass field behind a former industrial park in South Baton Rouge which houses the LSU Innovation Park. Weedy-looking stalks, in varying states of growth and decline, have busted out of their cracked planters and lean whichever way they please.
Cronin pulled up to the garden on a black Harley Davidson. He’s got red hair and a red beard and a kind of amazed gleam in his eye when he zeroes in on the special powers of these plants, their genetic freakishness, or their ability to outwit man’s expectations for them. He has studied grassland habitats for much of his career, and because of his garden and his work with the roseau cane, he is part of the consortium of scientists who are studying the invasive scale outbreak.
The roseau cane, which is hard not to find in Louisiana’s wetlands and one of the most widespread plants on Earth, still has its own mysteries.
He pulled a small stalk from one of the pots and tried to point out the tiny, wispy white hairs that distinguished the plant—which he calls by its scientific name, Phragmites—from the others. On another’s leaves, he indicated its particular bluish tint. (I nodded to convince us both that I could see it.)
Over the last decade, he has collected these plants from various corners of the continent and brought them back to to Baton Rouge. “Right now we’ve got 156 of these twenty-gallon pots from about ninety locations throughout all of the United States and a couple from Canada,” he said as we walked from row to row. He’s been to China and crossed Europe, collecting Phragmites samples for identical gardens in Denmark, the Czech Republic, Rhode Island, Australia, China, South Africa, and, soon, Argentina. Researchers, part of a group which he endearingly calls “Phragnet,” (Phragmite-network) collect data from these model gardens to share with each other and—eventually—us. “It’s probably the most widespread plant on the planet,” he said of Phragmites. “Almost to Antarctica you can find it. The southern tip of South America, Africa, Australia. It’s everywhere.”
He’s searched riverside and ditch for the plants in his garden, cultivated them, fought pests to keep them alive, and infested them with pests to see what would happen. The day before, when he had invited me to the garden, he sounded particularly excited because the plants and his team were nearing the end of a months-long experiment for the roseau cane scale research: “We infested my garden with scale insects that we’re going to be harvesting this week.”
He walked me over to one of the plants, pulled off a stalk, and, sure enough, pointed to one of the little brown specks responsible for so much destruction across Louisiana’s coast. The insect’s life, he said, begins as an egg inside its mother, under the brittle sheath of the cane. After it hatches, the new insect crawls a bit before finding a fresh spot to latch onto, feasting on the vital sap of the roseau, which weakens under the cumulative pressure.
Reports of how much roseau cane in the Lower Delta has succumbed to these massive die-offs now range from 100,000 affected acres to 400,000 acres. The insect has spread from the initial hotspots of Lower Plaquemines Parish all the way west to Texas and east to the Mississippi coast. As the roseau in the Lower Delta dies, the wetlands there have mostly converted to elephant ears and water hyacinth. According to Todd Baker, a biologist with the Louisiana Department of Wildlife and Fisheries, those plants “are exotic invasive species with little wildlife value to them.” This new wetland system, he says, “has no ability to resist erosion, and it cannot tolerate salinity, whatsoever.”
When I asked Miles LaRose, guide and owner of Shallow South Charters, about the roseau cane scale, he said the issue has to be put into the larger context of the Mississippi River Delta’s erosion. He’s witnessed what he describes as “unbelievable land loss in the last fifteen, twenty years” in southern Plaquemines Parish. He grew up fishing and hunting at a club below Port Sulfur, but by the time he was in high school, the camp’s central freshwater pond, once enclosed by marshes, opened up and became saltwater, which killed the grasses. “Eventually there was [practically] no land,” he said. “So the club just dissolved.”
It was two years ago that LaRose started noticing that patches of interior wetlands in Lower Plaquemines were thinning at alarming rates as hard edges of roseau cane started developing gaps. “Instead of having a large bush of cane, you’ll have a couple little stalks of cane by themselves,” he said. “So it’s basically a year or two before that just turns into water.”
The birdsfoot delta is the place where the Mississippi River, after traveling as many as 2,300 miles, finally reaches the Gulf of Mexico. It’s here that the muddy river water crawls slowly enough to drop its last bit of sediment: the lightest and finest stuff it could bear to keep a hold of. It’s a wonder that any land made of such delicate sediment can exist there. When a ship loaded with oil or soybeans goes steaming down a channel or a strong southeast wind blows up from the Gulf (let alone the swells of a hurricane), the water turns violent and rips at the land.
That land might not exist for long at all if it weren’t caught in the crosshairs of the roseau cane. If you can picture the thickest, most fibrous and stubborn knot you have ever fought to untangle, and imagine coating that knot in plaster, you might get a feel for the strength of a roseau cane root. Above ground, the roseau grows fifteen feet high and is impenetrably thick, but its real strength is belowground, where its roots can extend three or four feet deep like a brick, stuck out into the Gulf. According to Cronin, about sixty percent of the biomass of this tall, dense plant is under the ground. Cronin’s cracked plastic pots stand no chance against the roots’ ferocious urge to expand and spread.
He's searched riverside and ditch for the plants in his garden, cultivated them, fought pests to keep them alive, and infested them with pests to see what would happen.
Painfully slow watching it die
These roots are the first place where things get a little weird for the story of the roseau cane. I was shocked to learn that Cronin actually started his Phragmites garden ten years ago to study ways to weaken the plants, not to save them. The clogging qualities that make Phragmites such a treasure in Louisiana’s most vulnerable coastal wetlands are the same that make it the bane of waterways in other places across the country.
Cronin had been working closely with the managers of the Rockefeller Wildlife Refuge in Cameron Parish, where an invasive European strain of Phragmites has overrun up to fifty percent of the refuge. “It grows so thick and dense that it takes over habitat for wading birds; it clogs the waterways and makes them unsuitable for ducks.”
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This invasive European roseau cane has become infamous across the country, from the Chesapeake to the Great Lakes to Utah, where governments are spending millions of dollars every year to poison, burn, rip up, and control the plant, which can outcompete native vegetation and disrupt shellfish and oyster fisheries. Indeed, when I searched Louisiana duck forums expecting to find hunters alarmed at the roseau cane die-off, one of the few relevant posts on the matter was a homespun recipe of herbicides that could kill the plant. “It’s painfully slow watching it die and deteriorate,” writes the chemist. “Roseau is tough stuff and I’ve never been able to burn it like they do up North after it’s dead. But in the ponds [where] I’ve used it, it has stayed gone.”
When I asked Cronin if we were more at the mercy of these plants than they are to us, he said, “That’s certainly the case on the East Coast. They spend a lot of money trying to control Phragmites and they’ve not been successful at all. They’ve failed miserably at it. To control Phragmites, they literally go burn it and then cover the marsh with tarp to kill the roots and it’s incredibly labor intensive.”
Superplants
Cronin says the European Phragmites are resistant to every insect he’s tested it against. “It’s spreading really rapidly throughout North America, and we don’t really understand why it’s so successful,” he said, pointing to a sample, one of the tallest canes in his garden. He said that when word of the roseau die-off started reaching some of these communities fighting the Phragmites, people called to ask about exporting the scale insects for their fight. (Cronin declined.) Another post in the forum proposed importing the scale as well.
Not surprisingly, the invasive European Phragmites seems to be the variety most resistant to the scale insect, and Cronin imagines it will expand its territory on the delta naturally, though he doesn’t suggest we should rely on an aggressively invasive plant as a solution to an invasive insect.
Parasitoid wasps
I asked Cronin if his world was turned upside down when the Phragmites changed overnight from public enemy to victim. “Not necessarily,” he said, keeping things rational. “The Mississippi River Delta is a prime spot for invasive species. You know, it’s a major port for New Orleans and elsewhere. Lots of ships are coming in and out, carrying who knows what. It’s not surprising that invasive species come there.”
There have been three hundred years of ships traveling up and down the passes of the river and countless more when New Orleans was an indigenous trading port called Bulbancha. Take leaf, seed, stalk, wasp, root, nymph, tracked onto a ship by a boot, crate, or bilge water, add a lot of heat and water, and you get a slow-cooked gumbo where things have melded together, at times imperceptibly. Nutria, tallow, salvinia, hippo (almost), Asian tiger shrimp, giant applesnail, white Egyptian lotus, Phragmites.
Because of this mixing, researchers have come to Louisiana from as far away as Italy and China to look into the mysteries of how the cane has mixed in this gigantic, sprawling laboratory of marsh. “Worldwide, the greatest genetic diversity in Phragmites is in the Mississippi Delta,” Cronin said.
It wasn’t until fifteen years ago that anyone found out where the roseau cane in the Delta had really come from. Two Phragmites researchers, Carla Lambertini and Irving Mendelssohn, flew in a helicopter over the Lower Delta and mapped the various patches that appeared distinct. The researchers then took samples, analyzed DNA, and shocked everyone with the news that the predominant strain of roseau on the Lower Delta is not the North American-native “Gulf variety.” The vast majority of the roseau in the delta is actually native to North Africa and the Mediterranean. At some point in the last two hundred years, this “Delta variety,” according to Cronin, largely replaced the native Gulf variety without anyone realizing. “It probably makes up 99 percent of the roseau down in the delta,” he said.
Take leaf, seed, stalk, wasp, root, nymph, tracked onto a ship by a boot, crate, or bilge water, add a lot of heat and water, and you get a slow-cooked gumbo where things have melded together, at times imperceptibly.
In the garden, when Cronin pulled another sheath off of a cane stalk, I gasped at how big the scale was below: an egg-filled female the size of a watermelon seed, stuck there motionless. “Males are these puny little things that you hardly ever see, but the females grow these almost fingernail-sized scales,” he said. “And underneath that, the female will convert her whole body into eggs after the male mates with her.” From their mother’s dead body, the offspring could hatch and emerge as new scale insects, or they could emerge as parasitic wasps.
Cronin pointed to a tiny but distinct pinhole in the center of the female scale. “That’s a parasitoid that made that,” he said. “There’s five species of parasitic wasps. You’ll see thousands of these tiny, tiny wasps, smaller than the head of a pin, crawling up and down these stems, and they’ll lay an egg inside of every one of the eggs of these females. . .and then, instead of a new scale insect hatching from there, a fully-mature adult wasp will emerge.”
These wasps represent one of the few predators that could possibly curb the scale’s infestation. Strangely, they are also non-native and have come with the scale from East Asia. So far, two of the five species of the wasps have yet to make it to Louisiana, said Cronin. “Our group is trying to get a sense for what is going on with these in China. From there, maybe it will be the case that we’ll try to import more of these parasitoids, but that will be a long, drawn out process. A lot of permitting, a lot of experiments that would need to be done.”
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Cronin thinks it’s too early to tell what will happen with the roseau scale even in the near future. In late October, his team began the harvest and final count of the infested roseau in his garden. In all, the dedicated team will count every insect on hundreds and hundreds of stems. “My technicians are going bleary-eyed doing this. Not only do you count them, but you measure them for their size as well,” he said. The results could tell researchers which variety of the plant resists the scale most effectively and could be used for re-planting projects in decimated areas.
In the marsh, Cronin said, “The plants don’t look as if they’re in as bad a condition as last year at this time, but the insects are at their highest numbers.” He speculates that this could represent a new norm for the state: alternating die-offs and regrowth of the roseau cane, depending on the population of the scale insect, as the two species seek equilibrium. “It’s why populations cycle,” he said, “Outbreaks and crashes, outbreaks and crashes. It very well might be what happens here with these scale insects. Where we’re at now is a peak.”