Japanese stiltgrass (Microstegium vimineum (Trin.) A. Camus) is an invasive grass originally from Asia. This invasive weed is also commonly known as Nepalese Browntop. Japanese Stiltgrass was introduced to the United States in the early 1900s, believed to have arrived in Tennessee through packaging material. Since its initial introduction, there has been at least one other direct introduction to the eastern US. Since it arrived in the early 1900s, Japanese Stiltgrass has gradually spread across the eastern United States and beyond the Mississippi River. It has recently been found in neighboring states, with the closest locations to Iowa being in northern Illinois and southeastern Wisconsin. The plant was confirmed in Iowa as early as 2015. Still, there are currently only two confirmed populations: one in Polk County and another in Johnson County.
Habitat: Japanese stiltgrass is a widely adaptable weed that thrives in many conditions. Generally, it can be found on moist and disturbed sites, especially along floodplains. However, it can also be found in uplands, road ditches, and lawns/gardens. Due to its ability to grow in shade, it can grow abundantly in woodlands. Once in the woodlands, it can grow in dense patches that can shade and outcompete native vegetation.
Height: up to 3 feet
Leaves: Lance-shaped and approximately 3 inches long, with an alternating pattern on the central stalk. A distinctive silver midrib can be seen running slightly off-center through the middle of the leaves.
Flowering: in late summer, small flowers emerge from the tip of the central stalk.
Japanese stiltgrass has two mechanisms for spreading. One is by rooting at nodes along stems. This means they can easily form dense patches. It is also a prolific seed creator. Seeds form in late September and spread by wind, water, and gravity. Due to its ability to spread by both nodes and seed, Japanese Stiltgrass can form dense patches. It can readily take over the understory of a woodland due to its ability to survive in shade and outcompete native understory vegetation, reducing overall biodiversity. Patches of Japanese stiltgrass typically form loose, ankle-to-knee-high mats. In the fall, they turn a shade of light tan and will generally still be visible in their distinctive mat formation.
Control Methods
To manage stiltgrass, several mechanical and chemical methods are available for use. There are several important considerations with each control method. One of the most critical factors to ensure effective control is timing. The goal of control is to kill the plant before it can spread seeds. Any control method implemented after seeds have dispersed is typically ineffective, occurring from late August through September. It is also important to note that several years of control are necessary. Generally, seeds already in the soil can persist at least three years – meaning a population will continue to persist if control methods are not continued in consecutive years.
Mechanical removal, such as mowing or pulling by hand, can be effective if done in late July through August. Mowing too early may allow the plant to resprout and seed.
Prescribed fire can be effective if timed before seed set in late August to September. It is best to use prescribed fire with other methods for this plant.
With chemicals, always check the label. Ensure it is rated for use in the woodland setting and that any use is permitted as indicated on the label. Recognize that there may be damage to native plants as well if a non-selective herbicide is used. Visit our Chemical Control of Unwanted Vegetation page for more information.
Reporting
If you suspect you have identified a population of Japanese stiltgrass, some steps should be taken. First, take several photos to get a proper identification. These photos can be uploaded to EddMapS (Early Detection & Distribution Mapping System), a software used for tracking invasive species. Or send the images to your local forestry contact for verification. Next, contact your district forester to discuss the best management strategy for your property.
Remaining vigilant and proactive in identifying and managing Japanese stiltgrass is crucial for protecting Iowa's native ecosystems. By employing effective control methods and recognizing the signs of invasion early, we can work together to mitigate the impacts of this invasive species.
Additional Resources:
EDDMapS – Japanese Stiltgrass Interactive Range Map