Invasive plant gets stranglehold at Minto Park in Salem

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“They’re pretty flowers but they do a lot of damage"

City officials in Salem along with the Willamette Riverkeeper are fighting back against an invasive plant species at Minto Brown Island Park in Salem. (Courtesy Photo: Willamette Riverkeeper)

SALEM, Ore. (KOIN) — At Minto Brown Island Park in Salem, you’ll find ample of opportunities to recreate, but you will also find an invasive water plant growing out of control around the park

The city of Salem is working with the Willamette Riverkeeper to stop the spread of the aggressive and invasive plant that has gained a stranglehold on the Willamette Slough at Minto Brown. The Willamette Riverkeeper looks at water quality, habitat health, trash and other issues happening on the 187 miles of the river.

Uruguayan water primrose, also called Ludwigia, forms dense mats in slow-moving backwater channels, oxbow lakes, and sloughs, according to the city.

The yellow-flowered plant can choke entire waterways, severely restricting recreational access, degrading water quality, and creating an environment that is unfriendly to native fish and wildlife.

“If it was just one or two, it wouldn’t be a big issue, but the conditions have made it such that this plant has an advantage in the slough,” said Jen Mongolo, a natural resources planner with the city of Salem. “It starts to take over and when the plant takes over, it creates a monoculture across the slough… and impacts water quality and water temperature.”

An invasive plant seen in the water at Minto Brown Island Park in Salem. The park is a popular spot for kayakers and hikers. (Courtesy: City of Salem)

Mongolo added that the plants outcompete native vegetation and change the actual chemistry of the water by reducing oxygen levels, which increases the temperature. That then impacts the insects that live in the water that the fish, birds, turtles and other wildlife feed on.

What is being done?

Both agencies received a grant for $229,334, which includes $70,000 from the Bonneville Power Administration for the first year and $159,334 from the Meyer Memorial Trust for the subsequent two years. This is the third year of the project.

They hope to take control of the Ludwigia in the slough through the careful use of an aquatic-approved herbicide sprayed on the plants by state-licensed applicators.

“The goal is to reduce the plant’s population to such a degree that additional herbicide treatment will not be necessary once the project is complete,” said the city in a newsletter.

Richard Dickinson, a restoration manager with the Willamette Riverkeeper, said the plant comes from South America and doesn’t belong in this region but thrives in hot weather.

“It probably came via a fish tank or a backyard pond where people where people put nonnative species,” said Dickinson. “They’re pretty flowers but they do a lot of damage.”

The invasive species can grow up to five feet out of the water, which prevents light from getting through the bottom of the river or slough. Dickinson said this precludes other plants from growing.

However, this year – during the final phase of the project – organizers are planting native plants to help replace the Ludwigia they take out.

In the future, any new or remaining Ludwigia will be controlled by hand-pulling.

“It’s a high use recreation area. People love to go out there and kayak in the slough or hike around it,” said Mongolo. “I’m positive that the public did recognize a change happening.”

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