NEWBURY - The bikers and drivers passing by on Plum Island Turnpike, the fishermen on the riverbank, even the boaters eyed us curiously. Probably the pilots taking off from Plum Island Airport looked down and wondered what we were doing. On a sunny, scorchingly hot Saturday afternoon in June, we clambered around the muddy edges of the salt marsh yanking weeds.
But not just any weeds.
Perennial pepperweed - lepidium latifolium to the scientists - is the latest invasive species to threaten the health of the Great Marsh. Our group of fewer than a dozen was an early scouting party in what's expected to be a summer-long battle against the pest. The war will likely go on for years.
"We're worried about pepperweed because it's such a strong invader," said Sarah Janson, who, as pepperweed coordinator at Parker River National Wildlife Refuge, should know. "It replaces the native plants, trying to turn the marsh into a monoculture, a single field of pepperweed."
Already a major problem in Western states, the tenacious plant has begun to spread rapidly in Eastern Massachusetts and edge into New Hampshire. "The more we look, the more we find," Janson said.
Area residents are familiar with invasive plants, notably the purple loosestrife and phragmites.
"What might make pepperweed a little different," Jennifer Forman Orth, one of the authors of a key 2006 study of pepperweed, said by phone, "is that its spread is relatively new to our state, and that means we have a great chance to succeed in dealing with it."
In a time of bad news for the environment, from global warming on down, that's an opportunity not to be missed.
"I just feel if everybody pitched in, in some way, from recycling newspapers . . . to coming out here and pulling weeds, then the world would be a much better place," said volunteer Betsy Brown of Manchester-by-the-Sea. "People do get really discouraged and feel, forget it, we have no chance. But I don't believe that. I think everybody can pitch in and help the cause," and pulling pepperweed provides "instant gratification."
The afternoon began with an educational session at the refuge headquarters in Newburyport. Janson passed around samples of the plant and explained how to distinguish it from similar species. (The key: Alternating single leaves down the stem, instead of opposing pairs.)
Pepperweed likely arrived in California as a hitchhiker in a shipment of beet seeds from the Mediterranean in the early 20th century. No one knows how it arrived in New England, but the first reports came from Peabody in the 1920s.
Pepperweed remained relatively contained in a few spots in Eastern Massachusetts and Connecticut for decades before "exploding" in recent years, a progression typical of invasive plants, said Forman Orth, who is plant pest survey coordinator for the Massachusetts Department of Agricultural Resources.
"I have been to Yakima, Wash., and stood in a solid two acres of pepperweed," Forman Orth said. "We don't want to see it that bad here." Pepperweed spreads not only by seed but also via rhizomes - underground stems that make it particularly important to pull up as much of the plant as possible.
You can't just discard it, either, because even a small segment of stem tends to sprout new plants where it falls. At the refuge, a driveway is now used for drying pulled-up pepperweed plants until they're no longer viable.
Unlike many native species, pepperweed doesn't mind salt, so it's especially suited to the marsh. Its seeds can even survive long immersion in salt water, so the tides can spread them.
Once rooted, Forman Orth said, the plant acts as "a salt pump," bringing it to the upper soil from below, making life even more difficult for its neighbors.
"It threatens the integrity of the salt marsh ecosystem as a whole," said Forman Orth. "There are lots of animals, birds, fish, and aquatic invertebrates that rely on the native perennial species that pepperweed is displacing."
The Plum Island team's efforts involve either spraying a mild herbicide on pepperweed or uprooting it. Janson said the idea that pulling "could even be effective" came from the study by Forman Orth and her colleagues, which showed that in a few years it was possible to greatly reduce or even eradicate the plant in one spot.
More hands are always welcome. Janson's volunteers included everyone from members of Mass. Audubon to local high school students. Plum Island Kayak contributed kayaks and a leader last year for a pepperweed expedition up the Merrimack River, and will do so again, she said.
"I don't want to see the marshes go away. They're one of the most important parts of the planet because they're like a big filter, right?" said volunteer Elizabeth Szymanski of Plum Island. "Everybody's so yanked and cranked about the ocean, but this is as important to me."
Pepperweed is making inroads on New Hampshire's coast as well.
"Early detection, rapid response," said Kevin Lucey, restoration coordinator for the N.H. Coastal Program, who came along to learn from Janson's efforts. "We're looking at the same model of community support" to locate and remove pepperweed in the Granite State, he said.
Janson has several pulls scheduled in the coming weeks. To participate, contact her at 978-465-5753, ext. 203 . In New Hampshire, call Lucey at 603-559-0026.