In addition to fish, insects, and viruses, Pennsylvania faces a menace from invasive plants. Indeed, ornamental horticulturist Larry Kuhns believes the danger posed by invasive plant species is the most pervasive environmental threat of the 21st century. The fact that many invasives are cloaked in the guise of ordinary—and often attractive—plants makes their advance all the more insidious.

“Most people aren’t aware of the ecological damage invasive plants are inflicting on our biodiversity, our wildlife habitat, and our native plant species,” he says. “These plants are choking out and outcompeting native species. Compared to invasive plants, the chemical pollutants of the ’60s, ’70s, and ’80s will be considered an easy cleanup.”

Many species now considered invasive originally were introduced intentionally for conservation, wildlife, or landscape purposes. “Often, they were introduced into environments where there were no diseases or pests to control them,” says Kuhns. “They often are silent threats because most people aren’t aware of invasive plants or don’t notice them spreading into a new environment.”

A prime example is autumn olive, a fast-growing, large shrub that doesn’t thrive in woodlands, but quickly chokes open spaces when it becomes established. The Pennsylvania Game Commission cultivated and distributed it for years to be planted as a habitat improvement and food source for wildlife. “My father got some autumn olive plants for his farm from the Game Commission in the 1960’s, and now parts of the farm are overrun with it,” Kuhns recalls. “Pennsylvania has lots of abandoned farmland, and autumn olive thrives in those kinds of open areas. Once it gets started, it doesn’t take too many years to totally cover an abandoned pasture.”

Another invasive plant species that particularly worries Kuhns is Japanese knotweed. It grows in moist and aquatic environments, choking out native plants. “Japanese knotweed totally replaces whatever native plants live where it becomes established,” he explains. “And with the native plants go the insects and wildlife that depend on them.

“There are islands in the rivers around Pittsburgh that the Western Pennsylvania Conservancy manages for wildlife. Japanese knotweed has totally overrun them. The plants have gotten so tall and thick that waterfowl can’t even nest on the islands. The conservancy asked me what could be done about it. There are no practical ways of controlling this weed with physical methods, so all I could recommend was herbicides, but the conservancy did not want to use herbicides. It had to learn to live with the situation.”

Kuhns points out that knotweed is growing on the banks and islands of some streams in north central Pennsylvania, such as Pine Creek. “I canoe on that stream, and below the Pennsylvania Grand Canyon the banks are thick with it. It is eliminating native species. Roadsides and stream banks are continually disturbed, so they are conduits for the distribution of invasive plant seeds.”

Kuhns believes that most people are not aware of the threat posed by invasive plants because the problems have not been widely reported by the media. “We are never going to eliminate them, but we have to learn to control them in certain areas,” he says. “The key is to educate people about the risks posed by invasive species and teach people how to eliminate them before they cover hundreds of acres. We also need to do a better job of controlling these plants on roadsides because they spread from there to adjoining properties.”

Whether the threat comes from invasive plants, invasive fish, invasive insects, or invasive viruses, one thing is certain—it will not disappear anytime soon. Almost all invasive species are here to stay. Scientists may discover chemicals, predators, and protocols to control populations of invasive species, but it is unlikely that they will find ways to eliminate them, because the very traits and abilities that have allowed them to thrive in Pennsylvania’s habitats and environment will make them impossible to eradicate.

Many decades after the introduction of the gypsy moth and the sea lamprey, the best we can do is cope with their presence and attempt to limit the damage they do. If, in 50 years, we have found a way to wrest control of Lake Erie from the hordes of mussels and gobies, we should feel fortunate. Odds are they will still be there.

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Faculty and staff referenced in this article are Louise Bugbee, extension agent in Lehigh County; Robert Carline, adjunct professor in fisheries and wildlife; Hunter Carrick, associate professor of aquatic ecology; Herbert Cole, professor of agricultural sciences; Greg Hoover, senior extension associate in entomology; Steve Jacobs, senior extension associate in entomology; Larry Kuhns, professor of ornamental horticulture; and Jim Travis, professor of plant pathology.