It spreads like wildfire, blanketing entire landscapes in a sea of green that chokes out all other competitors. 

It is incredibly difficult to kill, constantly springing back to life like the villain in a horror movie. 

It has no native predators, but Dr. Bernd Blossey is trying to change that. 

Blossey, a professor in Cornell University’s Department of Natural Resources, is working toward a solution to curb the spread of Japanese knotweed, an invasive species wreaking havoc on ecosystems and infrastructure across the United States and much of the world. 

Blossey’s Cornell team is exploring a biological control for Japanese knotweed that has the potential to slow its steady spread across the American landscape. Researchers are hoping to introduce an insect native to knotweed’s home range in Asia, essentially creating a natural enemy where none has existed since knotweed was introduced in the U.S. in the late 1800s. 

This new “biocontrol” approach may be the last, best hope to prevent knotweed from taking over still more vulnerable acreage. 

“There’s no other hope for anything else,” said Blossey. “I don’t think you can be successful.” 

The stakes are high. Outreach by Cornell’s New York Invasive Species Research Institute regularly finds knotweed among the top concerns for land managers in the state. 

“Japanese knotweed is probably No. 1,” said Blossey. “Everybody is concerned about it, with the exception of the beekeepers who like the abundant flowerings in August and September. Everybody else wants to get rid of it as quick as possible.” 

With its hollow stems and large leaves, Japanese knotweed resembles bamboo. It forms dense colonies, often around waterways, and once established it will quickly dominate native vegetation. Knotweed can shoot up higher than 10 feet in a single growing season before dying back in the fall, leaving the ground vulnerable to erosion as it eliminates most other understory growth. 

Cornell researchers have found knotweed has a severe impact on amphibian populations due to disruptions to the natural food web around rivers and streams. Knotweed’s effect on fisheries and aquatic systems is not as well understood, but there is concern it could hurt the spawning habitats of valued fish species like trout and salmon. 

The problem is economic as well as ecological. Knotweed’s aggressive nature can damage the foundations of homes, underground drainage and septic systems, and other infrastructure. The problem isn't limited to North America. A study released in July estimated that invasive species have cost the United Kingdom’s economy nearly $7 billion over the last 40-50 years. Japanese knotweed was identified among the prime culprits, costing the UK about $57 million per year. 

Knotweed hits close to home for Blossey. It is prevalent in meadows around his home in the town of Richford in Tioga County. Blossey also watched with interest as a new shopping center was constructed on a patch of Japanese knotweed in Richford. Within a year, he was noticing knotweed pushing its way through the small cracks just outside the building.  

“The only way we know how to get into something that even remotely gets to eradication is deep excavation, six feet down, to get all the little rhizome pieces, and then put it in the landfill. That’s not feasible to do at any landscape scale,” said Blossey. “Maybe you could excavate that much for the foundation of a house, but it’s not possible elsewhere. You rely on other methods.” 

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Regular mowing can slow the spread of knotweed and may even kill isolated pockets, but most large thickets will return in a matter of weeks if the root system isn’t removed. Mowing also risks inadvertently spreading the plant, which is already ubiquitous in many areas. 

“When you drive along through the Catskills to New York City or in the Binghamton area where you have it flowering and you can identify it, it’s everywhere,” said Blossey. “You could mow it, it’s a good job creation program for everybody all the time, but as soon as you stop, it’s back with a vengeance. Mowing suppresses native species as well. They can’t tolerate the mowing all the time. 

“While you can kill some stems and individuals with mowing or herbicide, it’s not allowing native species to return the way we would be able to do so if biocontrol were successful. Mowing and herbicide are also incredibly labor intensive.” 

Biocontrol offers an alternative to costly containment efforts. Knotweed is kept in check by insects and fungus in its native range across eastern Asia, but it essentially has free rein in Europe and North America. Researchers have been attempting to introduce a sap-sucking insect native to Asia, the knotweed psyllid (Aphalara itadori), in the hope it could curb knotweed’s prolific spread across the land. 

The psyllid, the country’s first-ever biocontrol agent for knotweed, was approved for release in the U.S. in March 2020. Blossey and the Cornell team released more than 2,000 psyllids in June, dispersing one group near the Susquehanna River in the Binghamton area and another along a creek in Tioga County, both areas thick with knotweed. 

Early signs were encouraging. Blossey’s team returned to the protective cages the following week to find the insects had laid thousands of eggs, but the small creatures vanished when they were released to the wider environment. 

“They were really successful in reproducing in these leaf cages, but then they disappear outside,” said Blossey. “We think a lot of it is predation, but we don’t have full confirmation. There may be a combination of factors. No sign of them has been detected since.” 

Blossey’s findings mirror those of counterparts in the UK and Canada, where the release of the psyllid was approved ahead of the U.S. rollout. Similar releases were conducted last year across the U.S. in conjunction with the Cornell University effort. 

Aside from a single specimen observed here and there, all of the attempts at creating psyllid colonies appear to have failed.  

“There’s always the hope that maybe they did establish, they just didn’t like the site where we put them, or we can’t find them and in some years we will see them, but that has never happened in the UK or Canada where they have multiple years of observations already,” said Blossey. “It seems to be a dead-end for this particular insect.” 

Blossey remains undeterred, though. He already had doubts about A. itadori’s ability to impact knotweed populations, given previous research, and the Cornell University team is intent on visiting China and Japan to look for other organisms to enlist in the fight against knotweed. That research trip was supposed to take place this year, but the COVID-19 pandemic interfered. 

“We are not at the end of a potential biocontrol for the species, but this particular psyllid doesn’t seem to be a candidate we should bank on anymore,” said Blossey. “We’re doing more work. We have some candidate species we want to look at that do more damage to Japanese knotweed and then we will test the safety.” 

Cornell is equipped with a USDA-approved quarantine facility to ensure no insects are accidentally introduced into the environment. They must first prove compatible with native flora and fauna to avoid the devastation wrought by other invasive insects, such as the Asian longhorned beetle, emerald ash borer, gypsy moth and hemlock woolly adelgid. 

Introducing a biocontrol species to prey on another invasive species has worked in the past. Beetles that solely feed on purple loosestrife have helped reduce that fast-spreading plant in a process Blossey hopes to duplicate in knotweed. 

“My personal and scientific drive is trying to make sure we don’t lose the species that are conservation-reliant,” said Blossey. “Conservation is the big thing for me. That means we need to reduce the big populations of knotweed that we have. Biocontrol is never eradication. We don’t need that, but we need to lessen the impact Japanese knotweed has. That’s what I’m trying to do. There’s no other hope that I have, other than biocontrol.” 

Chris Potter can be reached at cpotter@gannett.com or on Twitter @ChrisPotter413. To get unlimited access to the latest news, please subscribe or activate your digital account today.