Defeating knotweed is hard, but possible
An Armstrong conservancy group recently beat back one of the region's most aggressive invasive species, Japanese knotweed.
A scourge for several decades, the giant knotweed species can tower 10 feet with its bamboolike stems and elephant ear-shaped leaves, smothering all natural vegetation in its path.
Knotweed has overtaken large portions of the banks of the Allegheny and Kiski rivers and other waterways over the last several decades.
The Allegheny Valley Land Trust, which owns 80 miles of trails in Armstrong, Clarion, and Jefferson counties, took on a half-mile swatch on its Armstrong Trail outside of Rimer, which was thick with knotweed.
It took 14 years to eradicate most, if not all, of it, said Ron Steffey, the land trust's executive director.
They mowed and they mowed some more, at least four times a year beyond the "green berm" of the sides of the trail.
Then, about four years ago, the land was clear enough for the Land Trust to introduce native sunflowers and milkweed, while nurturing the growth of shade trees such as sycamore and tulip poplar.
"It's been a success, but it's taken us a while to figure it out," Steffey said.
Japanese knotweed easily spreads because it reproduces not just one way but three ways: underground rhizome roots, seeds and easily transplanted plant parts.
And the battle is far from over, especially this year, he added.
The wet spring and early summer were conducive for the knotweed to grow at a time when it's difficult to mow.
It's bad, real bad
Japanese knotweed and the larger giant knotweed grow in floodplains, stream banks and lower slopes most everywhere in the three rivers area, said Charles Bier, senior director of conservation science at the Western Pennsylvania Conservancy and the Conservancy's representative on the Governor's Invasive Species Council.
Knotweed is so dense it has choked out native plants and shrubs that the general public is accustomed to not seeing.
"We have a whole generation of people who grew up in this landscape and have the impression that this is the way nature is supposed to look," he said.
Instead of knotweed, there really should be wildflowers lining the river banks.
Also lost is the ecological value of the native plants providing a home and food for birds, butterflies, moths, beetles and other wildlife, he added.
Knotweed is so much a part of the landscape, a silver bullet is needed to stop it, said Bier.
"It's good to hear about the success of the Allegheny Valley Land Trust," he said. "But if they would stop, the knotweed would return."
Tracking the knotweed is one way to fight the battle, according to Bier, referring to the project, Pennsylvania iMapInvasives program, which is collecting information on the location of invasives.
A history of effort
The Armstrong Conservation District has done a number of knotweed eradications projects over the years with varying success, said Dave Rupert, district manager.
The preferred method involves tamping down the growth of the knotweed and planting something else like wildflowers or pumpkins to overtake the invasive.
One experiment used pumpkin plants in Manorville but deer ate the pumpkin plants. Although there has been success with pumpkins elsewhere, Rupert said, Armstrong County hasn't been able to replicate it.
Suppressing the knotweed is the first stage, which takes three years of applying a chemical agent, preferably by a commercial sprayer, Rupert said.
Once the knotweed is at a minimum, native grasses and wildflowers can take hold in poorer quality soils, he said.
Efforts now are focused on preventing further spread of the knotweed.
The Armstrong County Conservation District works with contractors and others to make sure that soils with knotweed are identified and treated.
"Everybody recognizes it as a problem and everybody is figuring out what is the most cost effective solution to limit it from being spread," Rupert said.
Mary Ann Thomas is a Tribune-Review staff writer. Reach her at 724-226-4691, mthomas@tribweb.com or via Twitter @MaThomas_Trib.
