Knocking out knotweed

Research pins down a rogue invasive in the Pacific Northwest.


LUSH and verdant with heart-shaped leaves, Polygonum × bohemicum stirs in the breeze. To the uninitiated, it’s just a sprawling and rather tall riverside shrub. But to anglers, farmers, and landowners, the plant is bad news. Bohemian knotweed or false bamboo, as it is also known, is among the most prevalent invasive weeds in the Pacific Northwest and is notorious for spreading aggressively along riverbanks. It chokes streams and quickly edges out native plants that fish and wildlife depend on, eventually taking over and damaging the ecosystem it invades.

For the last nine years, government, nonprofit, and volunteer teams have battled infestations in Washington’s Chehalis River Basin, a watershed rich with diverse plant and aquatic species and home to one of the healthiest salmon runs in the country. Every year, these teams spend exhausting days searching for weeds and lugging backpacks of herbicide to treat infestations. But they are up against a master of survival. Stray fragments of knotweed stems or roots can start new infestations and undo their work.

Although scientists know a lot about knotweed’s devastating effects on native plants, not much is known about its effects on aquatic life. Ecologist Shannon Claeson with the U.S. Forest Service’s Pacific Northwest Research Station wanted to know how the weed affects fish habitat in Chehalis Basin streams. She also collaborated with knotweed teams to help them get ahead of the rogue weed’s next move.


Originally published in Science Findings. Read the full story here.