At Butternut Park in the small central Maine town of Chelsea, you don’t have to walk far to feel like you’re in a jungle.
State ecologist Justin Schlawin followed a park trail that runs along the Kennebec River into what initially is a typical floodplain forest. He pointed out maple and ash trees overhead and admired the diversity of plant species in the understory below.
“Whether it’s ferns or wood nettles, it tends to be really verdant,” he said.
But before long, the trail ended and the forest gave way to one species that dominates and forms a thick cover that towered over Schlawin, blocking out sunlight.
“So we’re standing in a shady, 8-foot-tall layer of Japanese knotweed. It’s very dense. And so we sort of had to push our way through to get through this vegetation,” Schlawin said.
Sometimes confused with bamboo, knotweed has a hollow stem and flat, shovel-shaped leaves as big as your palm. It’s been in the U.S. for centuries — initially brought here as an ornamental species. But it’s now considered one of the most invasive plants in the world and one of the most damaging in Maine.
Japanese knotweed can grow several inches a day, is strong enough to penetrate asphalt and can regenerate from tiny fragments no longer than your thumbnail. Here a single colony has swallowed half this forest — roughly four acres — transforming what should be a diverse landscape with dozens of species into a homogenous one.
“So we’ve entered the land of single species occupying this floodplain,” Schlawin said while surrounded by knotweed.
That makes this area less suitable for wildlife, like the woodcock and northern thrush, as well as the rare wood turtle. It also weakens an important function of this floodplain ecosystem.
“Floodplains, they are also important for flood mitigation,” Schlawin said. “They’re storing a lot of groundwater, there’s a lot of backwater sluice throughout floodplains that hold water during flood events.”
Schlawin said knotweed poses a significant threat to all floodplains in Maine. Even just a tiny fragment can start a new colony. Part of his job is to prevent it from establishing. But for sites like this one, the colony is so big there’s not much that can be done.
“It’s not going to be possible to treat a stand like this,” he said.
Getting rid of knotweed isn’t always hopeless. It can be done in certain places with the right tools.
“Alright, this is a good patch down here,” Amanda Devine said as she walked along a steep hillside near the shore at Woodward Preserve in Brunswick. She’s a botanist with the Maine Coast Heritage Trust, and she was there to remove knotweed.
Covered head to toe in a jumpsuit, rubber boots and gloves, she used a handheld injection tool to pierce a long, thick needle through a knotweed stem. It delivers a few drops of herbicide directly into the plant.
“It’s surprisingly woody,” Devine said. “You definitely don’t want to get your finger in between the target and this needle, because it’s a heavy duty needle.”
One by one, she injected herbicide into each knotweed stem thick enough for the needle.
“I think about it as chemotherapy. And if you’re a cancer patient, chemotherapy is awful, but it might save your life.”
Devine was trying to save this coastal hillside from erosion. Getting rid of the knotweed will allow native plants to reclaim the area as groundcover and keep the soil in place.
“This is a good one! This is about an inch in diameter,” she said as she kneeled down at the base of the plant. “I’m going to give this one two squirts.”
Because knotweed has an extensive root system, digging it out doesn’t work. And while using herbicide may not seem palatable, Devine said it’s an important tool. She applied it carefully and sparingly, and when possible, combined it with other methods such as smothering the plants.
Persistence is the name of the game.
“And you know what, there may always be a little bit of knotweed here,” she said. “But if we stay on top of it, if we don’t let it get too big, and we manage it, we don’t look for eradication, but we look for management and improvement, then, you know, that’s a victory too.”
A year ago, Devine said knotweed blanketed this hillside. But after an initial chemical treatment, she said it was reduced by 70 percent. And those kinds of results help to preserve Maine’s diverse landscape.
This article appears through a media partnership with Maine Public.
