Invasive Plants

Two Weedy Evildoers

By Linda McBride

Let’s talk about two very common weeds that can be seen most anytime we are wandering outside in a field or along a forest edge. They are so common, we likely think they are native, or more likely, we don’t give them much of a thought at all. But – aha – they are actually evil interlopers bent on taking over the little patch of Earth on which they find themselves!

The first evildoer is Japanese Stilt Grass (Microstegium vimineum) which is pictured at left. You may come upon a large patch of grass that looks a lot like a stand of mini-bamboo as you walk along a forest edge. If you look closely, you will see lance-shaped, alternate leaves that are slightly asymmetrical. A key characteristic is the silvery line that runs down the midrib. Sometimes its roots stick up a bit at the base, making the plant appear as though it is “on stilts.” This annual grass sprawls along the ground, rooting at nodes, spreading far and wide.

An Asian invader, stilt grass was first found in Tennessee around 1919. It was used as a packing material for porcelain, and that is likely how it came to be established here. It loves disturbance, such as flooding, construction, or mowing, and will spread rapidly, forming dense mats that can completely displace native vegetation. Even deer will turn their noses up at stilt grass, so there is little natural control.

Stilt grass flowers late in the season (July – September), forming seeds soon thereafter. Seeds are easily transported in water, by animals, on car and truck tires, and on hikers’ shoes and clothes. It’s always a smart idea to wash the mud off your tires or off your feet before leaving an infested area.

The best strategy for controlling stilt grass is removal of the plant before seed production, which can be accomplished by hand weeding or mowing. As the seeds remain viable for several years, this practice should be continued until no more plants emerge from the targeted area.

Any of our native ferns (like Royal, Sensitive, or Cinnamon), sedges (like Fox or Pennsylvania), grasses (like Wild Rye or Switchgrass), or vines (like Virginia Creeper, Cross Vine, or Trumpet Vine) that like part-shade to shade and moist soil would be excellent species to plant in order to keep the stilt grass from re-establishing after eradication.

The second evildoer is Chinese Lespedeza (Lespedeza cuneata) which is pictured at right. The tall, spiky stems of Chinese lespedeza are very familiar to anyone walking through fields or meadows or along roadsides and disturbed open ground. The stems can reach up to six feet in height, with woody root crowns. They tend to have a gray-green look to them. The leaves are thin, alternate, abundant, and three-parted.

Also an Asian invader, Chinese lespedeza was introduced in the late 1800s and was used for erosion control and forage. It is extremely aggressive, and can form dense stands in open areas and out-compete native vegetation. It is a perennial plant, and its seeds remain viable for decades. Its high tannin content makes it unpalatable to most native wildlife.

Chinese lespedeza flowers from July to September, with white, pea-like flowers with purple throats clustered in upper leaf axils. Fruits are single seeds in small pods clustered in terminal axils and scattered along the upper stem. During flowering, the plant’s root reserves are low, and mowing at this time will reduce plant vigor and prevent the production of more seed. Repeated for two or three years, this process will reduce the intensity of an infestation.

To make matters a bit more interesting, and perhaps confusing as well, there are two native lespedeza species in Virginia. One is Slender Lespedeza (Lespedeza virginica), which looks similar but has leaves that are slightly larger and flowers that are pink/purple, not white. Round-headed Lespedeza (Lespedeza capitata) is also somewhat similar, but its whitish flowers appear in larger, round-topped clusters.

In a meadow planting, either of the native lespedezas would be good choices to replace the Asian invasive, or you could try planting partridge pea (Cassia fasciculata) or any of our many sun-loving native grasses.

Next time you’re out for a walk, when you see these unwelcome guests, you can point at them, give your best evil laugh, and say, “Now I know who you really are, you evildoer! Be gone!” Or better yet, take action to eradicate them!