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Dangerous beauty
Pretty spring blooms hide an insidious threat from Bradford pear trees. They cross-pollinate with native pear tree species and yield sterile hybrids. Experts recommend eliminating Bradford pears from your landscape.
Photo by Jill Lang istockphoto.com
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Wicked weed
Inedible to livestock and difficult to eradicate, cogongrass crowds out native forage and has been found in 13 counties in South Carolina. It’s critical that any sighting of cogongrass be reported to the Clemson Department of Plant Industry by calling 864-646-2140.
Photo by Barbara H. Smith
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On the rise
English ivy is an aggressive evergreen vine that can reach heights of 90 feet or more. When allowed to climb a tree, its weight can cause the tree to break or uproot.
Photo by Barbara H. Smith
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Bad seed
Birds help spread Chinese privet when they eat the fruit and carry seeds long distances. This semi-evergreen shrub forms dense, nearly impenetrable thickets that consume farmlands, bottomlands, forests and abandoned homesites. It even grows in concrete cracks.
Photo by Barbara H. Smith
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The squeeze
Beauty aside, Chinese wisteria is the boa constrictor of the plant world—it will wrap around and overwhelm any desirable plants or trees in its path.
Photo by Barbara H. Smith
Invasive plants are the Godzillas of the plant world. They overtake the landscape, destroying native plant populations, affecting food sources of pollinating insects and other wildlife, and causing lasting environmental harm.
Fighting back isn’t easy. It can take years of labor-intensive efforts and diligent herbicide applications to eradicate an invasive plant infestation.
Invasive plants can grow quickly and spread by either seeds or underground rhizomes. That’s why gardeners should be cautious and vigilant about what we introduce into our landscapes, so we can prevent future problems. Part of the challenge is that growers and nurseries still sell some of these plants, so unsuspecting gardeners bring the problem right into their own yards.
Before selecting a landscape plant, do your homework. Make sure you are not introducing an invasive nightmare. Consult a reputable nursery to find desirable native and noninvasive plants that will add beauty and interest to your landscape without creating a monumental problem in the environment.
Here are some plants to avoid, as they are rated as chief threats in our state, according to the South Carolina Exotic Pest Plant Council:
Cogongrass (severe threat). Cogongrass (Imperata cylindrica) is such a devastating invader that it’s on the list of top 10 worst weeds in the world, as well as on both the Federal and State Noxious Weed lists. First imported from Asia in the early 1900s as a solution for erosion control, it spreads both by wind-blown seeds and by rhizomes and has such a dense growth habit, it excludes all other plants.
Cogongrass has sharp, silica-based leaves with white mid-veins and finely serrated edges. In winter, it’s an extreme fire hazard when its leaves die back. In spring, long, fluffy, white seed heads are produced prolifically. Unpalatable to livestock, it can’t be used to feed grazing animals. Worse, because of its voracious growth habit, it displaces desirable forage grasses.
Home gardeners have been drawn to a cultivar of cogongrass called Red Baron or Japanese blood grass (Imperata cylindrica), which was sold on the perennial market in years past and admired for its attractive red and green leaves. But, watch out: It is now illegal to grow, sell or even plant Japanese blood grass in South Carolina, because it can revert to the green parental cogongrass form.
Infestations can begin innocently, such as when unsuspecting gardeners see a beautiful, flowering grass growing on the roadside, slam on brakes and dig up a sample to plant at home. Then comes the nightmare. Once cogongrass is introduced, it begins its tenacious spread. (Can you hear the theme music from Jaws?)
Cogongrass has been found in 13 counties in South Carolina and has already spread all over Florida, Georgia, Alabama, Mississippi and Louisiana. It’s critical that any sighting of cogongrass be reported to the Clemson Department of Plant Industry, which will eradicate it and monitor the site for new activity for years. Thanks to this department, all known sites in South Carolina have been eradicated and are constantly monitored. If you spot cogongrass, report it immediately to keep this destructive threat under control.
Autumn and Russian olives (severe threat). Little wonder that these attractive plants have tempted gardeners with their flowers, colored fruit and fragrance. Grown as shrubs or small trees (Elaeagnus spp.), they were introduced from Asia in the 1930s for use as ornamental plants, wildlife habitats and erosion control. But, they are a prime example of a good intention gone bad. Like all introduced invasive species, they displace desirable and native plants.
Elaeagnus may grow to heights of 20 feet or more, sending out long shoots with 2- to 3-inch thorns. Leaves are alternately arranged along the stems, green on top and silver with small dots underneath. In early fall, they produce pale yellow to white, sweet-smelling flowers, followed by small, brownish fruit drupes that turn red when ripe. Seed production is high—as many as 200,000 seeds per plant. The drupes are eaten by birds and other wildlife, spreading seeds for miles.
Elaeagnus tolerates drought, shade and salt, growing easily along roadsides and fences, in forests and on cleared land, and they flourish even in poor soils. Be careful when shopping: Elaeagnus plants are still available in the nursery trade, so don’t be tempted to buy them.
Bradford pear (significant threat). Common in suburban landscapes, Bradford pears (Pyrus calleryana Bradford) were introduced into the nursery trade from China during the 1960s. They were widely planted and favored for their white, early-spring flowers and intense fall color. The round, small, olive-brown fruit produced in May and June are sterile, so they can’t reproduce.
On the down side, Bradford pears have a weak branch structure and are susceptible to major damage by wind, ice storms and microbursts. Newer cultivars, such as Cleveland Select and Chanticleer, were bred for better limb structure—but herein lies the problem. When Bradfords began cross-pollinating with these newer, callery pear cultivars, it created an aggressive pear that chokes out other plants. The fruit produced by these new cultivars are not sterile. Birds and other animals eat their seeds and spread them for miles.
Many Bradford pears are grafted onto callery pear rootstock; root sprouts emerge from the stock and cross-pollinate. These evil spawns have 4-inch thorns that cannot be mowed down and are sharp enough to puncture tractor tires. When they bloom in spring, you can see how they spread across open fields, power lines and vacant land. Not only do they threaten natural ecosystems, there’s considerable economic cost in managing and eradicating these trees, both in time and in the heavy use of herbicides.
Don’t plant Bradford, Cleveland Select, Chanticleer and other ornamental callery pears. In fact, most reputable nurseries will not sell them to the unsuspecting public. If you have them in your landscape, remove them, and plant a more suitable substitute.
English ivy (severe threat). Introduced from Europe by our Colonial ancestors, this familiar ivy (Hedera helix) is an aggressive evergreen vine that can reach heights of 90 feet or more. It climbs by aerial roots, meaning it can produce aboveground roots along the stem. This “spiderman” plant easily attaches to trees, brick, stone and other surfaces. When allowed to climb a tree, it harms the health of the tree, and its weight can cause the tree to break or uproot.
Ivy will tolerate shade and will grow in moist to dry conditions. You’ll recognize immature English ivy plants by their dark green, waxy leaves with three to five lobes, giving them a star-like shape. With an aggressive growth habit and a tendency to form dense mats, ivy will inhibit and crowd out other herbaceous plants, shrubs and trees. It also threatens other plants as a secondary host for bacterial leaf scorch, which infects oaks, elms and maples.
Chinese privet (severe threat). This semi-evergreen shrub (Ligustrum sinense) arrived in the United States from China in 1852 as an ornamental shrub that can grow up to 20 feet tall. Privet produces a cluster of white flowers in the spring, and the drupe fruit matures from green to a blue-black in early fall. Birds and animals who eat the fruit spread the seeds long distances. Seeds are also spread by water in flooded bottomlands.
Chinese privet can also spread by root sprouts and form dense, nearly impenetrable thickets. It will consume farmlands, bottomlands, forests and abandoned homesites. It even grows in concrete cracks. This tenacious plant thrives in full sun to heavy shade, so it will grow just about anywhere it becomes established.
You might see several variegated privet cultivars on the market. As with the Japanese blood grass, these cultivars can revert to the green parent species and become invasive; don’t buy them. The variegated forms produce no fruit, but when branches revert to the solid green form, fruit are produced prolifically.
Chinese/Japanese wisteria (severe threat). Two species of wisteria (Wisteria sinensis and W. floribunda) were imported from China and Japan in the early 1800s. With their beautiful lavender, violet, pink or white, pea-like spring blooms, these vines were sought after to plant as porch vines or trained shrubs. Beauty aside, wisteria is the boa constrictor of the plant world—it will wrap around and overwhelm any desirable plants or trees in its path. It invades open or disturbed areas after control burns, land clearing or mowing, producing new shoots wherever they are trimmed or pruned. Often, a wisteria invasion starts near an old homesite where it was planted as an ornamental. If your property is covered with Chinese or Japanese wisteria, you can thank the ancestor or former owner who planted it next to the veranda years ago. This is an unwanted heirloom.
Both species have a rampant growth habit. They root by surface runners and can also spread by seed dispersal. But, they mainly spread by vegetative means, rooting at each node.
Easy ways to tell them apart are by the bark and by how the massive, trunk-like vines grow. The bark of Chinese wisteria is a brownish-gray, and the vine twines in a counterclockwise direction, while the Japanese species grows in a clockwise direction and has a whitish bark. Both have large, velvety, bean-like seedpods that ripen in the fall. The Japanese species has larger blooms and is more fragrant than the Chinese. The two species have been known to hybridize, creating a completely new species.
Instead of the Chinese and Japanese wisterias, plant American wisteria (Wisteria frutescens), which is native to the U.S. It grows at a slower rate than its Asian cousins, blooms heavily in late spring and blooms again lightly in the summer. Its flowers attract butterflies and are an important host for silver-spotted and long-tailed skippers. It’s an aggressive vine; when planted in the landscape, it needs a strong support structure. Like Chinese wisteria, American wisteria twines counterclockwise. Look for Amethyst Falls, an improved selection of American wisteria commonly found in the nursery trade.
BARBARA H. SMITH is a consumer horticulture agent at the Clemson Extension Home and Garden Information Center based in Clemson. Contact her at barbar6@clemson.edu or (888) 656-9988.
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15 invasive plants commonly found in South Carolina
Here are 15 invasive plant species commonly seen in South Carolina yards and landscapes. The threats range from “alert,” which indicates plants that are absent from or limited in South Carolina but are severe threats in neighboring states, up to “severe,” which are well-established in our state and threatening S.C. ecosystems. “Significant” threats are invasives that are established, spreading and causing damage.
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Get More
The Clemson Department of Plant Industry is responsible for monitoring, positively identifying and eradicating cogongrass in South Carolina. To get updates on invasive species and find a link for reporting sightings of cogongrass or Japanese blood grass, visit clemson.edu/invasives or call the department at (864) 646-2140.
For a complete list of invasive plants that threaten South Carolina ecosystems, see the South Carolina Exotic Pest Plant Council website, se-eppc.org/southcarolina/invasivePlants.cfm.
Need help with ideas for what to plant in your yard? Find details on plants that grow well in South Carolina from the Carolina Yards Plant Database, clemson.edu/extension/carolinayards/plant-database/index.html, and the S.C. Native Plant Society, scnps.org.