SCARBOROUGH — Starting this month, a coalition of conservationists will began the second round in a three-year plan to combat an invasive reed in Scarborough Marsh.

A strand of phragmites australis, which is native to Europe, has become a pervasive pest in the marsh, spreading quickly and growing up to 10 feet tall. Local and state experts say the phragmites block out the sun and that their vast root structures suck up more than their fair share of nutrients, effectively choking out the native marsh plants like cattails and the less aggressive, nearly identical indigenous phragmites.

According to Katie Fellows, a board member of the Friends of Scarborough Marsh, about 100 acres of the 3,200-acre marsh were “infected” with phragmites when the herbicide treatment began last year. Contractors mowed phragmites stands and applied a cocktail of herbicides to the leftover stems.

The project has a three-year budget of about $68,000, funded by state and federal grants and some donations from the Friends of Scarborough Marsh. Aside from the herbicide application by Connecticut-based contractors Innovative Mosquito Management, the project involved mapping and research by the Friends, Scarborough Marsh Audubon Center and the Maine Department of Inland Fisheries and Wildlife.

Scott Lindsay, an IF&W regional wildlife biologist who oversees the efforts at the marsh, said there was about an 80 percent success rate last year.

“Now we’re going through again, and we have identified some sites earlier this summer, where the plants were still coming up,” Lindsay said. “We marked them on a map and gave them to our contractor.”

Lindsay said that including phragmites stands that rebounded after last year and other stands found since then, he and the contractors would tackle about 20 acres this year.

The herbicides applied to the invasive reeds include Monsanto’s Rodeo, the major ingredient of which is glysophate, and Habitat, a trade name for the herbicide imazapyr.

Both chemicals are non-selective, meaning they kill any plant with which they come in contact. But they have been deemed safe to humans and other animal life when used properly. They’re applied both by hand and with a large machine, like a plant-killing water cannon.

Lindsay said that while it may sound like the non-selective nature of the spray is dangerous to indigenous, “good” marsh plants, the cross-kill factor won’t be a problem.

“Phragmites doesn’t grow in association with good plants,” Lindsay said. “By its very nature, it creates a monoculture. If you walk through these phragmites stands, you won’t find any other plants there with it.”

To eradicate the phragmites completely would take a much finer microscope than available, but by the end of this season’s efforts, Lindsay and the others hope to have whacked the reeds down to about 5 percent of the coverage they enjoyed before the herbicide application began last year.

Next year, they will pore over the marsh, looking for any stragglers that may have escaped the herbicide. As an incentive, Lindsay said 10 percent of Innovative Mosquito Management’s payment will be withheld until the 95 percent kill-rate is achieved.

Mario Moretto can be reached at 781-3661 ext. 106 or mmoretto@theforecaster.net. Follow him on Twitter: @riocarmine.

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Phragmites australis, as seen in Scarborough Marsh. The invasive strand of this common reed comes from Europe, grows quickly, and chokes out indigenous plants in the marsh.

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