What Weed Is That?
Invasive Japanese Stiltgrass
Microstegium vimineum has many common names; annual jewgrass, bamboo grass, shady crabgrass, painin deassgrass (just kidding… I made up that last one) but the name most recognized in our area is Japanese stiltgrass.
An Invasive Plant
Stiltgrass is considered an invasive plant (non-native plant that spreads quickly). Like all invasive plants, if left unchecked, it can displace native plants and disrupt local ecosystems. It can grow in home lawns and wooded areas with as little as 5% direct sunlight. It is native to Asia but today can be found throughout the Southern and Eastern U.S. First documented in Tennessee in 1919, M. vimineum is thought to have made its way to our shores as packing material in cases of fine china.
Germination and Habitat
Like crabgrass, Japanese stiltgrass is an annual grassy weed. New plants will germinate from seed in spring and thrive during summer where they overwhelm desirable plants and causing most of their damage. They set seed in August before dying off each fall. Unlike crabgrass, stiltgrass loves the shade. While it can spread to full sun, it is usually found in shady lawns, roadside ditches and wooded areas.
As with any invasive plants, it is recommended to control the spread of stiltgrass wherever possible. This means getting it before it goes to seed in late summer. In unmowed areas, it can reach 2-3 feet in height and small patches can easily be pulled out as the root system is shallow. With larger natural areas, it is effective to severely cut it back just before the plants flower so it can't produce seed. However, this strategy does not work in your home lawn.
With frequent mowing, microstegium adapts and can set seed on plants one to three inches tall. The good news is that the same pre-emergent that controls crabgrass also controls it's shady cousin. The bad news is that stiltgrass germinates earlier then crabgrass so a standard four step program is generally not effective. The key is to make your pre-emergence application early in the spring (late February/March) which necessitates a follow up application (late April/May) to ensure good control throughout summer. If you miss the boat on preventive treatments, there are several post-emergence grassy weed controls that are effective.
Be on the look out for this foreign invader and, regardless of your political persuasion, don't turn a blind eye. Get rid of it.