Heather N. Kolich, ANR Agent, UGA Extension Forsyth County
Take a walk around your neighborhood, a county park, or a natural woodland, and the chances are high that you’ll encounter at least one invasive plant species. Invasive plants, insects, and animals are introduced both intentionally and accidentally. When they escape into nature, they become bad actors, causing ecological problems by outcompeting or consuming native plants and wildlife and agricultural plants.
Two invasive species that are easy to identify now are mimosa, because it’s blooming, and Japanese stiltgrass, because it’s nearly everywhere.
Mimosa trees (Albizia julibrissin) are also known as silktree, powderpuff tree, and Japanese mimosa. Native to Asia, it was brought to North America in mid-to late 1700s as an ornamental plant. Mimosa trees have multiple, graceful stems, compound, fern-like leaves, and fluffy pink flowers that bloom in early summer. Unfortunately, each flower produces multiple long seed pods containing numerous viable seeds. The seed pods can float, so they can travel far downstream to pop up in new locations. In addition to reproducing by seeds that can hang out in the soil for years before germinating, mimosa trees reproduce by root sprouts.
Mimosa trees readily establish in disturbed soil, old fields, and along the roadsides. As they spread, they create dense colonies that gobble up soil nutrients and block out sunlight, effectively choking out native plants. The loss of biodiversity has negative effects on native wildlife and birds, who depend on native plants for food, nesting materials, and shelter.
For non-chemical control of mimosa trees, hand-pulling seedlings is effective. Larger sprouts can be exhausted by repeatedly cutting them to the ground when they sprout back up. Cut down trees or girdle the trunk by removing a wide swath of bark all the way around or cutting into the trunk all the way around to stop the flow of nutrients and water. Scout for and cut of root sprouts that will push up around the tree as it dies.
Herbicides such as glyphosate and triclopyr can also be used to control mimosa sprouts and smaller trees. Read and follow label instructions.
Japanese stiltgrass (Microstegium vimineum) is also called Nepalese browntop, Asian stilt grass, bamboograss, and Chinese packing grass, in recognition of its arrival in the U.S. It was used as packing material to ship porcelain goods. It was first reported in 1919 in Tennessee, where some of the packing grass apparently contained viable seed matter. Since then, Japanese stiltgrass has colonized 16 states and risen to the second place ranking in the Georgia Forestry Commission’s worst twelve nonnative invasive plants list.
Japanese stiltgrass is a sprawling grass with a nodding, droopy habit and long, asymmetrical, slightly hairy leaves. A silver line runs the length of leaves on the top surface, and the midrib is off-center. It grows 2-3 feet tall and looks like a small, delicate bamboo.
It is a shade-tolerant, summer annual grass that also thrives in full sun. It reproduces only by seeds, but the stems can root at the nodes during the growing season. This habit helps the grass spread and increase rapidly. It overruns and displaces native understory vegetation.
Japanese stiltgrass flowers in September and produces copious seeds in September and October. The grass dies back with frost, but seeds can remain viable in the soil for up to five years. Reported ecological impacts of this invasive grass include changes in soil conditions, including significantly raising soil pH and creating inhospitable growing conditions for native plants; degradation of nesting habitat for native wildlife; and reducing the plant diversity and density of woody species, particularly oaks and understory shrubs.
Fortunately, it is a shallow-rooted grass and is easy to pull up. Removing Japanese stiltgrass before it flowers prevents additional seeds entering the soil. Frequent mowing can also prevent formation of the flowers and subsequent seeds.
Several herbicides that control grasses are also effective in controlling Japanese stiltgrass. A mid-February application of a pre-emergence herbicide labeled to control annual grasses, such as products with active ingredients pendimethalin, dithiopyr, and trifluralin, can prevent seed germination.
Active management of invasive plants is necessary to preserve the native biodiversity that supports a healthy, living, local ecosystem. Now is a great time to target these two bad actors, mimosa and Japanese stiltgrass, for removal from our landscapes and forest lands.