Invasive plants can have a slow but devastating effect on an ecosystem.
By outcompeting native plants for resources like sun and water, they reduce natural diversity, alter soil conditions and, ultimately, wipe out native wildlife habitats.
“It starts with the insects, then the birds that eat them and all the way up the food chain,” said Blake Moore, Delaware Invasive Species Council chairman. “It’s just really important to protect our native plant species here in Delaware.”
Moore is also a horticulture and natural resources agent at the University of Delaware Cooperative Extension. He has a bachelor’s degree in natural resource management and previously served as a noxious weed specialist for the Delaware Department of Agriculture.
Which invasive plants are most concerning depends on who you ask. Since Moore’s experience is mostly in rights-of-way, which include roadsides, trailsides and other places plants are free to grow wild, such as new housing developments, he’s most concerned with plants that grow in these areas.
There are five invasive plants at the top of his list this spring:
- Tree of heaven.
- Porcelain berry.
- Japanese stilt grass.
- Callery pear.
The key, according to Moore, is awareness: knowing not to plant them, being able to identify them when they pop up, then eliminating them from the environment.
Many invasive plants, however, are so persistent they require a professional to eliminate. Moore recommends contacting the University of Delaware Cooperative Extension for help.
1. Tree of heaven
Tree of heaven (ailanthus altissima) is anything but heavenly. In Delaware, it’s an environmental double whammy. Not only is it an invasive plant, but it plays host to an invasive insect, the spotted lanternfly.
Plus, it stinks — literally. It’s sometimes called “stinking sumac.”
Native to China, tree of heaven grows rapidly and is a widespread invasive species in North America, according to The Nature Conservancy. It spreads quickly through root suckers.
“This one is so hardy and able to spread that we’ve seen it growing out of the sides of buildings in the city,” Moore said. “But more often along roadways or behind shopping centers, places like that.”
2. Porcelain berry
Porcelain berry (ampelopsis brevipedunculata) is not only a roadside blight but a woodland invader.
Its roots often entwine themselves with the roots of other plants, while the vine can stand alone or grow over and around native trees and shrubs.
“I constantly have to cut it off of my dogwood trees,” Moore said. “It grows very vigorously.”
Native to northeast Asia, porcelain berry easily outcompetes other plants by growing in dense thickets, blanketing the land and smothering other species.
It spreads through extensive root systems as well as bird droppings. Birds eat porcelain berries when there aren’t enough native berries available.
3. Japanese stiltgrass
Japanese stiltgrass (microstegium vimineum) is an annual grass that easily invades disturbed areas. Numerous blades grow from one stalk, giving it a bushy look. Each blade has a silver streak that runs down the middle.
Land that is regularly mowed or flooded and foot-trafficked areas like trails are especially susceptible to Japanese stiltgrass, according to the Brandywine Conservancy.
It thrives in all sorts of environments, with sun and moisture levels running the gamut. It grows in dense patches, crowding out native species.
Unlike some other invasive species, Japanese stiltgrass is easy to pull. Mowing, too, can be an effective way to prevent stiltgrass from spreading, but it has to be timed precisely, just before flowering in September.
4. Callery pear
Those beautiful white-flowering trees blooming along Route 1 right now? They’re Callery pears (pyrus calleryanas).
“They’re going to be very visible over the next few months,” Moore said.
Callery pears were popular ornamental trees throughout the 20th century, but they have a tendency to split or break, especially during storms. New, sturdier Callery pear cultivars, with one type known as Bradford pears, were bred to eliminate that problem.
In what turned out to be a much bigger problem than breaking limbs, the cross-pollination of the cultivars caused the species to spread at a rapid rate.
Callery pears now dominate many roadside landscapes where native species once reigned.
Virtually all natural resources agencies are asking the public not to plant Callery pears and to consider removing any already existing on their properties.
If you were considering a Callery pear for your yard or landscaping project, Moore suggests the native Eastern redbud, flowering dogwood or serviceberry instead.
The common reed (phragmites australis) is everywhere in Delaware.
“They’re a classic example of how invasive species can really change a landscape,” Moore said.
According to the Chesapeake Bay Program, “phragmites” comes from the Greek word “phragma,” meaning “fence,” indicating just how impenetrable stands of phragmites can be.
“It’s a really hard one to control,” Moore said. “Most of the time land managers are the ones undertaking efforts to get rid of them.”
Phragmites can grow as high as 18 feet, according to the U.S. Fish and Wildlife Service, but more concerning is how far they grow beneath the ground. Phragmites mainly spread through rhizomes, which are epic underground stem and root systems.
“Getting rid of them is a multiyear effort,” Moore said. “We’re never going to be able to completely eradicate them, but smaller areas can be rescued.”
The aggressive phragmites frequently takes over wetlands and areas adjacent to water, destroying important wildlife habitats. The reeds themselves provide little to no food or shelter to wildlife.