Fighting the takeover of invasive plants

Now that we're becoming more knowledgeable about what constitutes invasive vines, what should we do about them?

Communities organize weed walks so residents can help pull or dig them, and federal, state and local maintenance crews are cutting down, spraying and removing vines that smother forests with their rapid growth. But individual gardeners often ask what they can do to fight the invasion of non-native plants.

Kudzu (Pueraria lobata) is probably the best-known invasive alien, first introduced to this country by Japan at the 1876 Centennial Exposition in Philadelphia. Its flowers, with their sweet fragrance, appealed to American gardeners. But this Asian vine's growth habit became evident quickly. Stems can grow as much as a foot a day with the ability to smother huge areas of trees, returning annually for a repeat performance. It has invaded the Southeastern United States and been found as far north as Long Island, N.Y.

The Southeast offers the perfect climate for Kudzu, allowing it to grow out of control. In Virginia and Maryland, it is covering large areas of land along the banks of the Potomac River.

The only known controls are non-selective herbicides that are not supposed to be used near water. Mowing, tilling, pruning and pulling it out by hand are some ways to hold it at bay. If you leave one root piece in place, the kudzu will return quickly.

The latest work in biological controls is enlisting the help of leaf-eating beetles, weevils and seven or eight fungi sent from China that might keep the plant under control. Some promising work is being done at the University of Delaware's College of Agriculture and Natural Resources. However, further work is necessary to ensure that these biological controls don't negatively affect native plants.

Porcelainberry (Ampelopsis brevipedunculata) is one of the most common vines I notice in this region. A native to Asia, and now North America, it has beautiful blue-to-purple berries that can be seen hanging from bridges, trees, telephone poles and wires, growing through and covering many ornamental shrubs in summer. Birds are the most common way that the seeds of this invasive vine are spread. It only takes one season for porcelainberry to grow a taproot that requires a weeding tool to remove it.

Challenge to control

Porcelainberry can be controlled with a non-selective herbicide, but the challenge is to keep the spray only on that plant. The least-toxic way to remove it is by hand weeding with a digging tool, after a rain. It's great exercise and most rewarding when you capture the entire taproot. Use gloves in case you encounter thorny plants through which the vine is growing. If you grab sharp leaves you can draw blood.

Wild grapes vines (Vitis sp.) are more common than you might think. There are at least eight species that are native to North America, growing from New York and New England into the Southern states. Grape vines can be confused with porcelainberry, so get a positive identification from your county extension service before eating or making wine from tiny berries you find on native vines. Porcelainberries won't harm you if you eat one. It is in the grape family, but without the sweet flavor of ripe wild grapes. Wild grapes are also an environmental threat to shrubs and trees due to their rapid growth, and birds help spread the seed. Considered weeds in nurseries and gardens, they can smother native plants that wildlife need to keep the ecosystem in balance.

If you grow grapes, control them by keeping just a few growing on an arbor, plucking the fruit in September and October. Prune vines in November to keep seeds from spreading. The native wild grape vines with their sweet, tiny grapes are not invasive provided you keep them pruned. Treat them as edible grapes. An excellent site for learning the proper cultural techniques for pruning Asian and European grapes is available at gardening-howto.com.

Cross-vine (Bignonia capreolata) is a native plant but can grow out of control. A semi-evergreen, it will become quite woody if grown where it is happy. This little-appreciated vigorous native plant has a beautiful flower but requires attention after several years. Since it is considered a native in Maryland and Virginia, west to Illinois and south to Florida, this area is an excellent location to grow one. It thrives in sun but prefers a protected site. Grow it on an arbor, fence, trellis or wall. It flowers on last year's growth and, depending on the hybrid, it may flower sporadically throughout the season. The colors are orange-brown to red. As I stated, this plant is native to our region but needs to be pruned and trained to control it.

Chinese Wisteria (W. floribunda) is a weed. It is the Asian wisteria that escapes into the wild in sun or shade and overgrows every object it contacts. Chinese wisteria can twist ornamental iron supports into a tangled mass. I pull about 10 to 12 seedlings a year that try to commandeer our woods. We do not dare to neglect them for more than one growing season. Moist soil is the easiest medium for pulling these weeds. In youth the taproot of this invasive vine is the same length as the top growth. In China, they have natural enemies for control - leaf-eating insects and fungi. This vine volunteered in our yard and now adorns our rear deck. We watch it very closely, pruning the spent flowers and seedpods, and pruning the long whips. We make a last cut at the end of the season, taking the side stems back to spurs of two to three buds. That is where it should flower from in early spring. The original volunteer is so happy that it has flowered every year since it was dug and planted at our deck.

Be a responsible citizen

I'm not advocating that everyone go to such lengths to keep an invasive wisteria. You should be a responsible citizen and remove the Japanese wisteria that can become a weed and replace it with American wisteria (W. frutescens). It is a beautiful plant that is more graceful and has a smaller flower and foliage than the coarse-textured, invasive Japanese variety that we have at our home and don't want to surrender. But alien plants escape from gardens and out-compete less-vigorous native flora that wildlife depend on for food and habitat.

Mile-a-minute weed (Persicaria perfoliatum, formerly Polygonum perfoliatum), also known as Chinese tearthumb, is a diabolical invasive vine. It arrived from Asia in ornamental nursery stock and was first identified in Portland, Ore., in 1890. It was identified again in Beltsville in 1937, but neither site had infestations. The origin of the infestation is attributed to a nursery in York County, Pa. Between the 1930s and 1946, mile-a-minute was grown by the nursery owner, who had an interest in the plant and allowed it to get out of control. Since then, it has spread about 300 miles in several directions. Sharp down-turned thorns on the stems and leaf veins will tear the skin of anyone who grabs this weed, which appears soft to the touch.

There are no selective controls, and non-selective weed killers can poison waterways. Until another control is found, it should be mowed, scraped, plowed or dug up and removed before it goes to seed. Its presence is increasing every year.

Although not all texts agree, there is a fairly widespread opinion that we will lose our ecosystems. I am not a native-plant purist, but I agree that locally native flora is the most logical material to nurture. To clarify what vegetation is native to particular regions, use the database offered by the U.S. Agriculture Department at plants.usda.gov. More information about native species is available at natureserve.org.

You can identify invasive and native plants on the Web sites of the Maryland Native Plant Society, mdflora.org, and the Virginia Native Plant Society, vnps.org.

Joel M. Lerner is president of Environmental Design in Capitol View Park.