Five Notorious Invasive Plants in Northern Virginia
Emily Ellis
It goes without saying that there are a wide variety of plant species at the Oak Spring Garden Foundation. But if we had to choose five of the most tenacious, widespread, and unwelcome species on the property, it would be the five invasive offenders listed below.
In a globalized era when the movement of species is inevitable, non-native plants are here to stay. Not all of them are bad; as the climate changes and many species begin to redistribute themselves, scientists continue to debate how to classify native, non-native, and invasive plant species. Certain species are generally labeled as invasive due to the economic or environmental harm they can cause in their non-native ecosystem. While these plants cause no trouble on their own turf, when unleashed in foreign environments, they can wreak havoc by crowding out native species, contaminating the soil, and other damage.
At the Oak Spring Garden Foundation, managing invasive plant species falls to our Arboriculture, Conservation, and Landscapes team. They take a lot of factors into consideration when it comes to invasive species control, including the species type, the severity of the infestation, and the location on the property. Some of the methods the ACL team employs include controlled burns, herbicide use, and total removal, all of which must be applied year after year in order to get a handle on these pesky plants.
To wrap up Invasive Species Awareness Week, we’re discussing five top troublemakers at the Oak Spring Garden Foundation, and what we do to manage them. Scroll down to read more.
Tree of Heaven (Ailanthus)
Photo by Sarah Causey
To conservationists and property owners, this species, which was introduced from China in the 1700s, is more like a Tree of Hell. It’s easy to see the appeal this tree had for unsuspecting horticulturists centuries ago: it is attractive with its elongated leaves and sunset-colored seed pods and grows rapidly, quickly creating shade in gardens, landscapes, and in urban areas that would be inhospitable to many other species. It has also made its way into popular literature, and was the titular tree in Betty Smith’s A Tree Grows in Brooklyn.
Spotted lantern fly. Photo courtesy of USDA
Now for the bad: rapidly-growing ailanthus can crowd out native species and excretes allelopathic chemicals into the soil that can limit or prevent the establishment of other plants. It also is the host plant for the spotted lantern fly, an invasive insect from China first discovered in Pennsylvania in 2014, which can cause extensive damage to fruit trees and has been spotted in neighboring counties to Fauquier.
What to do about it:
It’s not easy, but there are several methods that can help you in your fight against this hellish tree, which will likely need to be applied over a period of years. If you spot ailanthus seedlings, pulling them by hand, roots and all, is probably the simplest method (seedlings closely represent root suckers, however, which are far harder to remove). With grown trees, the “hack and squirt” method, in which herbicide is applied to the tree’s tissue through a cut made in its trunk, can be an effective treatment for tree of heaven (Curtis Wurth, who heads Oak Spring’s Invasive Species Management Team, demonstrates this method in the video below). Our friends at Blue Ridge PRISM (Partnership for Regional Invasive Species Management) also provide a great factsheet about identifying and controlling tree of heaven.
Oriental Bittersweet
Photo credit: Richard Rowley via Wikimedia Commons.
A tolerant, quick-growing vine that was introduced to the U.S. in the late 1800s as an ornamental plant, oriental bittersweet, with its red berries nestled in golden casings, quickly made its way into holiday décor. By the 1970s, it was labeled as an invasive species due to its rapid spread through native landscapes and its tendency to strangle and smother even large, mature trees.
While many of us are guilty of using bittersweet in holiday arrangements, cutting it for this use has helped facilitate its spread throughout U.S. forests over the decades (it is even illegal to sell and cultivate in some states). Native American Bittersweet is a much better choice for landscaping and holiday wreaths.
What to do about it:
Oak Spring’s ACL team has been using basal oil spray (an herbicide mixed with oil, sprayed directly onto the bark of a plant) to target Oriental bittersweet, as well as other woody invasives, through the winter. After late May/early June, foliar spray is effective on plants small enough to be sprayed safely. Find Blue Ridge PRISM’s factsheet about Oriental Bittersweet here.
Garlic Mustard
It’s likely that you’ll see some garlic mustard sprouting this spring: the rampant invasive weed particularly likes to spread in shady forests and along roadsides and stream banks. The big trouble with garlic mustard, which is native to Europe and was likely first brought to North America by early colonists as a food source, is that it can inhibit soil fungi, threatening the growth of native species.
Perhaps garlic mustard’s one good quality is that it is edible and contains substantial amounts of vitamins A, C, E. The leaves make a good substitute for basil in pesto, and the spicy roots, when grated and mixed with salt and vinegar, make a tasty “horseradish” - a good use for all those weeds you have to pull up!
What to do about it:
The best way to get rid of garlic mustard is to tear it up by hand, which can be quite a tedious endeavor depending on how large your infestation is. It should come up easily, roots and all. Since the plant is non-toxic and has no spines or thorns, this is even an activity you could enlist your children to help with! Just make sure to dispose of the whole plant in a plastic bag. Avoid mowing garlic mustard when seeds are present (May - September) as this will spread the plants. Find more information about garlic mustard here.
Multiflora Rose
Photo: Ryan Hodnett
Multiflora rose may have an innocent name, but its behavior in North American forests and farmlands is anything but. Like many aggressive introduced plant species, multiflora rose was first brought to North America for ornamental purposes: it was imported from Japan to be used as rootstock for rose gardens in the 1800s. However, this pretty plant soon escaped cultivated areas. Able to thrive in a variety of environments, it alters the structure of grasslands and forests, shading out native flora and climbing and smothering taller plants.
What to do about it:
This winter, our ACL team has been using basal oil spray to target multiflora rose and other woody invasive species. The oil helps the herbicide better adhere to and penetrate the bark. Since it targets bark and not the leaves of the plant, our team is able to carry out this work in winter when the landscape is less brushy and there are fewer ticks. They also cut down larger specimens in the winter, and use a foliar spray on the new growth that emerges in the spring. Read more about multiflora rose management here.
Japanese Honeysuckle
Japanese honeysuckle’s leaves remain green in the winter.
Japanese honeysuckle’s heady scent and clusters of nectar-filled blossoms may remind you of lazy summer days, but despite its pleasant appearance, this plant can be trouble. Japanese honeysuckle was first introduced to North America in the early 1800s as an ornamental plant. It is currently classified as a noxious weed in Virginia due to its tendency to smother and kill native vegetation and suffocate shrubs and saplings by girdling.
If you’re in the market for honeysuckle for your garden or landscape, there are several native species that are even more beautiful and a far better fit for North American ecosystems.
What to do about it:
In addition to the basal oil and foliar treatments they use on most woody invasives, our ACL team does a fair amount of mechanical work during the winter to get a head start on invasive management, cutting large honeysuckle bushes with hand tools or a brush cutter and then foliar spraying new growth in the spring. Read more about managing Japanese Honeysuckle here.
Interested in getting a handle on your own invasive species? Keep an eye on our newsletter and website - we’ll be announcing two workshops with Blue Ridge PRISM (Partnership for Regional Invasive Species Management) on invasive plants of Northern Virginia later this year!
Thanks to OSGF Invasive Management Control Team leader Curtis Wurth for his help with this blogpost!
Banner image: OSGF’s ACL team implementing a controlled burn to manage invasive plant species growing on the margins on one of Oak Spring’s ponds.