Invasive Japanese knotweed worse than kudzu, threatens East Tennessee ecosystems

Knoxville

The visceral response a patch of Japanese knotweed evokes in scientists, naturalists and homeowners might surprise you. At first sight, the plant's small, red, asparagus-like heads poking through soil or pavement look innocuous enough — you might even call them cute.

Adjectives in the scientific community differ: "relentless," "disastrous," "destructive," "annoying," "devastating," "thuggish." Publications show the plant no mercy, because given an inch, knotweed can take over a mile.

The 'scourge' of the South, maybe the world?

"It is a scourge," said Daniel Simberloff, an environmental scientist at the University of Tennessee. "I've seen it around Knoxville, especially on stream edges. It is certainly a problem in areas of East Tennessee and Western North Carolina."

More:Which plants helped shape Tennessee? Kudzu, cotton and ginseng on the list from survey of residents

Simberloff said the plant can grow at a rate of about 4 inches per day, and grows both by spreading seeds and by its creeping, "monster-sized" underground rhizomes.

Daniel Simberloff, an environmental scientist at the University of Tennessee, points out features on the Japanese knotwood, an invasive plant appearing in East Tennessee, in his office on UT's campus on Monday, June 3, 2019.

"Cutting it back makes it re-sprout, and the rhizomes make excavation almost impossible," said Belinda Ferro of the Tennessee Invasive Plant Council. "If even a tiny little bit breaks off, it can create a whole new colony."

The Tennessee Invasive Plant Council classifies knotweed as a severe threat that can only be controlled with strong herbicides.

"That makes it more problematic because small pieces of the rhizomes spread so easily down streams and in riparian areas," she said. "But you don't want to use any kind of glyphosate-based herbicide near a stream."

Great Smoky Mountains National Park forester Kristine Johnson said foresters started to try to eradicate this patch of Japanese knotweed near the Bullhead Trailhead in 1998. First, they tried injecting herbicide, but it did not work. Eventually, they were able to control the site by cutting the weeds down and dabbing herbicide onto the stumps. It took 20 years of herbicide applications to free the area of the knotweed infestation.

Dangerous to ecosystems and property values

The World Conservation Union has listed knotweed as the “world’s worst invasive species." Japanese knotweed was first introduced in Europe as a fast-growing plant with potential as a cattle feed, an ornamental plant or a erosion control plant. But without the control factors of its indigenous environment, the weed quickly spread over the United Kingdom where the government now classifies pieces of the plant as controlled waste.

Mortgage companies have refused applications for United Kingdom properties with knotweed because it can sprout through walls, floorboards and foundations.

Panic over declining property values reached fever pitch in England six years ago when Kenneth McRae, of Birmingham,bludgeoned his wife with a perfume bottle, killing her and then himself. In a suicide note, he claimed fear of a patch of Japanese knotweed growing over the couple's fence "disturbed the balance of his mind," English newspapers reported.

More annoying plants:Grab your chainsaw and end this Bradford pear curse once and for all

The plant was introduced to the United States in the 1800s for erosion control and for use in gardens, but has now become widespread in about 41 states, according to the United States Department of Agriculture.

Ferro said she has not yet heard of the plant taking over buildings in Tennessee, but it's possible the problem to could reach the magnitude it has in the United Kingdom if the plant continues to spread unchecked.

"What a plant does somewhere else can be a clue to what the plant could do here," Ferro said, adding the infestation appears to be worse in northern states.

"But, just like any other invasive plant, it really can tolerate just about any condition and colonize pretty much anywhere," she said. "The more immediate danger is to the ecosystem. It travels along corridors and along streams, and it can really displace native vegetation."

Knoxville Utilities Board said Japanese knotweed is one of several invasive plant species they encounter in East Tennessee.

Pretty but horrible:Villainous beauties: How fragrant mimosas really stink

"At this time, it has not had a large impact on our system, and is managed through hand-cutting, mechanical cutting and herbicide where appropriate in our utility right of ways," KUB spokeswoman Stephanie Midgett said.

SUPPORT LOCAL JOURNALISM: Get unlimited access to the Knoxville News Sentinel for a low price

Quickly rising up to 10 feet tall in spring, the imposing, arched stems of Japanese knotweed quickly smother native plants when it moves into a new area.

Competing with kudzu in East Tennessee

Driving north on Interstate 75 in East Tennessee, huge knotweed colonies are visible along the sides of the road.

Kristine Johnson, supervisory forester for the Great Smoky Mountains National Park, said she's been "shocked" to see large knotweed infestations that have spread in the over parts of Cocke County, north of Hartford in the last 10 years.

"It has covered kudzu!" she said.

Park foresters have been keeping an eye on knotweed populations spreading from a repair and construction company's property near the park boundary.

"It is infested with kudzu, wintercreeper and knotweed, which is likely to spread into the park soon," Johnson said.

Japanese knotweed is an invasive plant and has recently been seen in East Tennessee.

Controlling knotweed in Smokies, national forests

Inside the park boundaries, Johnson said the parks service carefully inspects all quarry and soil material imported into the park to prevent knotweed and other invasive species from spreading through root fragments.

"This plant is a serious problem for small creeks because it de-waters streams needed for agriculture and natural resources," she said.

Foresters have successfully managed a knotweed infestation in an area of the Bullhead Trailhead, but it took about 20 years of annual cutting, herbicide injections, sprays and stump dabbing to knock it out.

But they have not found a way to manage a widespread knotweed colony in a riparian zone of the West Prong Little Pigeon River along the Spur, Johnson said.

"We are unable to manage this effectively because of infestations on tributary creeks outside the park which flood regularly, bringing new knotweed roots and seeds," she said.

Highway 441's lanes border the site on each side, preventing the infestation from spreading into the rest of the park, but, she said, it has begun springing up in downstream areas of Sevier County.

The Cherokee National Forest has run into similar issues as upstream infestations carry knotweed rhizome segments into the park boundaries.

Mark Pistrang, a botanist/ecologist for the Cherokee National Forest, said for the past five years, the forest service has been treating more than a dozen areas where knotweed growth has impacted the Ocoee River Gorge, forest biodiversity or recreational access.

"Unfortunately there's a huge source upstream of us and that's a huge risk," he said.

Near the river, Pistrang said contractors have treated the knotweed with aquatic herbicides.

"We've not been able to eradicate it, but I think we've certainly reduced it," he said. "It's difficult to completely eradicate it. You'll treat it and then someone will find a brand new start somewhere, and you don't notice it until you've already got a clump of it growing."

A Knox News subscription gives you unlimited access to stories that make a difference in your life and the lives of those around you. You also get the ability to tap into news from the USA TODAY Network's 109 local sites.

News Sentinel staff reporter Monica Kast contributed to this story.

Reach Brittany Crocker at brittany.crocker@knoxnews.com. Follow her on Twitter @brittcrocker.