How to combat North Carolina’s invasive plants

Many North Carolina Botanical Garden employees spend half their time patrolling for invasive plants. Aggressive imported vines are constantly trying to sneak into its 700 acres, and it takes constant vigilance to keep them at bay. Then, when these folks go home from work, they’re often battling the same species at home.

“It’s a big deal,” says Johnny Randall, the botanical garden’s director of conservation programs. “Controlling invasive plants takes up probably half of everyone’s time or more.” This same breakdown is common at other preserves too, he notes. Invasive plants are everywhere.

Kudzu is one of the most common offenders. It can blanket entire areas, smothering whatever plant life was there before. Wisteria is notoriously hard to kill, while Oriental bittersweet and English ivy present their own challenges in the local landscape. It’s not just other plants they hurt, either. Caterpillars can’t always digest their leaves, which means fewer butterflies. These plants’ fruits are often sugary and low in protein or fat. Migratory birds that eat these fruits, Randall says, are effectively choosing candy bars over cheeseburgers. These plants aren’t from North Carolina, and they’re lousy houseguests, wreaking havoc on the existing ecosystem if not properly controlled.

“Like all organisms on earth, they evolved with other organisms. It’s been demonstrated fairly well that plants brought from other lands to anywhere, especially if it’s on a different continent, leave (their) pests and pathogens behind,” Randall says. “You rarely see insects or fungal damage or viral damage on invasive plants. That’s one of the reasons they are invasive.”

Randall shared practical tips on controlling some of North Carolina’s more insidious invasive plants.

Wisteria: “Wisteria and a number of invasive plants are really problematic because they have such extensive root systems,” says Randall. “You really cannot pull them out so it’s almost like you have to turn to the dark side and use herbicides.” If you just cut the vine off at the ground, he says, everything aboveground will die, but the plant will send out a signal of sorts, causing sprouts to emerge elsewhere. The underground root system really is immense, and wisteria is tenacious.

“My recommendation would be to paint that cut area with some herbicide and that will oftentimes kill the underground portion,” Randall says. It is possible to knock out wisteria without herbicide by cutting every single stem of wisteria over the course of several years, but it really can take five years or more to wear the plant out. With herbicide, Randall says, never spray a vine that is climbing a tree or on something. The risk of drift is too great.

Fall is the best time to cut and paint vines like wisteria because nutrients are currently moving downward through the plant, toward its root system.

Kudzu: “That is one of the easier plants to control, even on a large scale,” says Randall. Kudzu often grows from a cluster of crowns, he says, which you can find by scrambling through the vines. Randall credits Newt Hardie of the Kudzu Coalition with determining that if you chop off the crown, the entire plant dies, roots, vines and all. Or, there’s always the cut-and-paint technique mentioned above.

Some people use goats to control kudzu infestation. “Using goats is like using a string trimmer or a brush cutter,” Randall says. “Of course things sprout back.” Kudzu, however, is nutritious for goats. If it’s on a huge scale – covering several acres, perhaps – Randall recommends hiring a professional.

English ivy: This popular landscaping plant, Randall says, tends to invade the botanical garden from adjacent neighborhoods. It’s especially insidious, he says, because it’s an evergreen. When it climbs on a deciduous tree, it can add too much extra weight during ice or snow storms, which kills the host tree. “The roots are fairly shallow, so you can pull it out, even over large areas,” Randall says. “That is a herculean task. There are some herbicides that work well.” Cut and paint, he says. Cut and paint.

Oriental bittersweet: Oriental bittersweet is shrouding so many areas, Randall says, draping trees along the Blue Ridge Parkway corridor, but also in the Triangle area. “At least Oriental bittersweet can be successfully pulled without using herbicide,” Randall says. “It is really, really important to cut those vines from trees to keep them from sending fruit. The fruits are ripening now, just in time for the fall migration of birds. It’s a big deal.”

Prevention: “The answer is for your neighbors not to grow invasive plants, especially those that might be dispersed by birds,” says Randall. “Wisteria and kudzu are two plants that tend to have fruits that aren’t too widely distributed by birds.” Vines like Japanese honeysuckle, porcelainberry, mile-a-minute vine, Oriental bittersweet and English ivy are problematic because birds can carry their seeds long distances.

This story was originally published September 16, 2016 at 9:20 AM with the headline "How to combat North Carolina’s invasive plants."