ST. JOSEPH — For several years, Southwest Michigan residents have been battling the fast-growing Japanese knotweed, and making slow but steady progress in eliminating the destructive plant.

But just when you thought it was safe to go back into the outdoors, a number of other invasive species – plants and pests – have taken root or are on their way here, an expert warns.

These non-native species cause $138 billion in damage nationwide, and almost $6 billion in the Great Lakes region, according to Jared Harmon, an invasive species outreach educator with the Berrien Conservation District. He spoke this week as part of the St. Joseph library’s summer lecture series. They also harm almost half of the endangered species, he said.

Invasive species are non-native to the region where they are found, and cause harm to the economy, environment and health, Harmon explained. The plants usually sprout earlier and grow faster, giving them a head start over surrounding flora, sometimes choking out other organisms and contributing to habitat loss.

They often are introduced by humans, Harmon said, and the seeds can hitch a ride via shipping or on agricultural equipment.

Japanese knotweed, which originated on the sides of Asian volcanoes, was brought here as an ornamental plant but quickly wore out its welcome. The plant can grow up to four inches per day and reaches 12 feet tall. More damaging, it has a deep root system that can break through concrete and asphalt and damage underground pipes and the foundations of houses.

Digging it up or cutting it down spreads seeds that further expands its reach, requiring herbicide treatments. Killing off Japanese knotweed can take three to five years, Harmon said. The city of St. Joseph is in its third year of trying to eliminate the plant in ravines where sewer lines run.

Japanese knotweed is not the only species knocking at the door.

Kudzu, known for blanketing much of the southern U.S., has shown up here, with one patch on private property in Berrien County and two stands in Van Buren County, Harmon said.

With its purple flowers, Harmon said he at first thought it was a grape vine. Like knotweed, it grows extremely fast, as much as one foot per day, and a six-foot section can weigh 400 pounds.

Some species are more than a nuisance. Giant hogweed, found at 70 sites in Michigan, presents a health risk. It is carcinogenic and causes severe skin reactions. It can even cause temporary or permanent blindness, Harmon said.

Not all the menaces come out of the ground. The spotted lanternfly, which eats the sap from grape vines, fruit trees and other plants, is found in Pennsylvania and other states, and will likely be in Michigan within three to five years, Harmon estimated.

There isn’t a plan at this point to confront the crisis. “We’re holding our breath on this one,” Harmon said, conceding that experts need to do a better job communicating with fruit growers about the potential risk.

Humans aren’t helpless when it comes to staving off invasive species, Harmon assured his audience, and there are various methods for dealing with different invaders. Cutting and mowing doesn’t always work because it can spread seeds, as with knotweed, and herbicides have to be applied carefully, he said.

Predators can be introduced to reduce the plants, but that runs the risk of the insects becoming invasive. Harmon said Michigan State University Extension is researching predators that could curtail Japanese knotweed.

One surprising strategy is using goats to eat the plants, Harmon illustrated. This has a limited impact on the surrounding environment, but it’s expensive, he noted. One caveat is that the goats eat everything around them, not just the invasive plants, and apparently they have to get along with each other or they lose their appetites.

People can assist researchers by reporting the presence of invasive species through the Michigan Invasive Species Information network’s phone app, which helps “citizen scientists” and professionals to identify and pinpoint suspect species for further study. Information is at www.misin.msu.edu/apps.

Contact: jmatuszak@TheHP.com, 932-0360, Twitter: @HPMatuszak