Japanese stiltgrass—also known as Nepalese browntop (Microstegium vimineum)—is an annual grass, native to Asia, that can reach more than 3 feet 6 inches in height and can form extensive colonies (Figure 1). It was likely introduced accidentally as packing material in shipments from its native range (Kleczewski, et al., 2011). It was first found in North America near Knoxville, Tennessee, in 1919 (Landschoot, et al., 2020).
Japanese stiltgrass is very adaptable. It can tolerate low-light environments with sufficient soil nutrients and moisture. Conversely, it can tolerate low-nutrient and low-moisture environments with adequate light (Leicht, et al., 2005). Adequate nutrients, moisture, and light, allow it to thrive and out-compete most native understory plants. It commonly establishes along forest edges, logging roads, recreational trails, ditches, stream corridors, and areas with disturbed soils (Figure 2). It is also found in floodplains; moist, early-successional fields; and along utility corridors where it is not exposed to full sunlight.
Stiltgrass can produce 100–1000 seeds per plant. The seeds can persist in the seedbank for more than three years. These seeds are dispersed by several mechanisms including foot traffic, water movement, mowers, equipment, and wildlife (McGill, et al., 2008). Consequently, stiltgrass can spread rapidly, especially when aided by disturbance that exposes bare mineral soil. Where white-tailed deer are abundant, their preferential browsing on native plants and avoidance of stiltgrass may further facilitate the spread of this invasive grass.
Identification
- Leaves—Leaves are flat, pale green, asymmetrically lance-shaped, and about 1–3 inches in length. They are also sparsely hairy on both sides and along the margins. A shiny, off-center mid-rib is conspicuous on the upper surface (Figure 3). The leaves are arranged alternately along the branched stem and project outward from it. Leaves have a long sheath collar with fine hairs that encircle the stem.
- Stems—Stems are branched, slender, wiry, and covered by overlapping leaf sheaths. Nodes and internodes are hairless. Stems are green but change to purple and brown late in the season.
- Flowers—Delicate, spikelike flowers up to 3 inches long develop in late summer or early fall in the axils of the leaves or at the apex of the stem. Flowers may be unbranched or with 1–3 lateral branches on a wiry stem. Spikelets are paired.
- Seeds—The seed is a tiny, husked, ellipsoid grain. Seed heads are thin and sometimes persist through winter. Seeds can mature within 2–3 weeks of flowering. Some flowers are self-pollinated and do not need to open to produce viable seeds (Neal & Judge, 2023).
- Roots—Distinct aerial roots or prop roots can be found at the lower nodes. As an annual the root systems are shallow and fibrous (Figure 4), which distinguishes stiltgrass from the native white grass (Leersia virginica)—a perennial with a stout rhizome.
Early Detection and Rapid Response
Once Japanese stiltgrass becomes established in an area, it can spread rapidly and form dense monocultures that can suppress most native plant species. These well-established populations can only be controlled with a substantial investment of manpower and resources over a long period of time; therefore, early detection and rapid response are two cost-effective keys for keeping this species at bay. Early establishment nearly always occurs along roadsides, stream corridors, and trails. Rapid expansion usually occurs following disturbances such as timber harvests, extensive flooding, or construction projects; therefore, it is essential to be vigilant, to regularly scout for, and to control this species, especially prior to a planned harvest or other soil-disturbance activity. It is also very important to monitor recently disturbed areas and control emerging populations before they become established.
Spread Prevention
Since mowing, road maintenance, and timber harvesting equipment can rapidly spread stiltgrass, it is imperative that equipment is inspected and cleaned on a regular basis. When possible, mow non-infested areas prior to mowing areas with known stiltgrass populations. Loggers and other contractors should be required to sanitize equipment prior to moving it to your property. Care should be taken to prevent movement of any above-ground plant parts. Debris from mowing and road maintenance equipment should be disposed of properly.
Since stiltgrass can be spread by foot traffic, horses, and recreational equipment, cleaning boots and equipment can help to limit the spread of seed into non-infested areas. Place high priority in controlling stiltgrass along trails, especially those leading to non-infested areas. Consider rerouting trails that pass through infested areas.
Gravel, topsoil, seed, and mulches are another way stiltgrass can be inadvertently moved from one place to another. When possible, purchase these products from certified, weed-free sources or at minimum, check with local suppliers to be sure products do not come from locations infested with stiltgrass or other non-native invasive plants.
Control Methods
Although many control techniques have been attempted with varying levels of success, a few cost-effective control methods have minimal impact on native plant populations. Most control methods will need to be repeated for several growing seasons, since control is rarely 100% effective and the seed of stiltgrass may remain viable in the soil for up to 5 years.
Mechanical Control
Hand-pulling can be an effective method of controlling isolated, small populations of stiltgrass. This is rarely practical once stiltgrass becomes well-established.
Hand-pulling is most effective late in the growing season before seeds mature. Pulling earlier in the growing season can be futile, since seeds in the soil can continue to germinate well into the growing season. Pulled plants should be bagged and removed from the site to prevent seeds from maturing after they are pulled.
Mowing is another control mechanism that has been successfully utilized to manage stiltgrass, but its application is limited to roadsides, open areas, and trail systems that will accommodate mowing equipment. A string-type trimmer or weed eater can be utilized to mow sites that are not accessible by larger equipment. A string-type trimmer is ideal since the plants need to be cut off at ground level as stiltgrass can regrow from remaining stem nodes (Landschoot, et al., 2020). To be effective, mowing must take place late in the growing season just prior to the establishment of the flowers (Neal & Judge 2023). Mowing earlier in the growing season can limit the height growth of stiltgrass, but the plant can still flower and produce seed. Mowing accessible areas is more effective when combined with other control methods in adjacent, infested areas to minimize recolonization from neighboring populations.
Chemical Control
Non-selective foliar herbicides such as Roundup, Accord, and other glyphosate-based products, can be applied to the foliage of stiltgrass at any time during the active growing season (Table 1). Since these products have no residual effect, control is most effective when applied in late summer just prior to flower development to ensure contact with individuals that germinate later in the growing season. Using higher concentrations of labeled rates for non-selective herbicides will kill most contacted plants, therefore these treatments should be limited to monocultures or small, isolated populations of stiltgrass not growing near desirable plant populations (Swearingen & Adams, 2008). Where a mixture of native plants and stiltgrass exist, utilizing a glyphosate-based product at a lower rate (0.5 % vol./vol.) can be effective against stiltgrass and should have minimal impacts to native perennial species (Table 1). Other native annual plants or plants that are particularly suspectable to glyphosate may also be impacted at this lower rate. Application later in the growing season can reduce exposure of native spring ephemeral plants to herbicide treatments.
When treating stiltgrass populations in wetlands or along streams, be sure to use a glyphosate product, such as Roundup Custom, that is approved for use in and around aquatic sites.
Non-selective pre-emergent/residual herbicides with the active ingredient pendimethalin (e.g., Pendulum) can prevent stiltgrass germination but will have no impact on plants that have already germinated (Table 2). They must be applied early in the spring—2–3 weeks prior to seed germination. Other herbicides, such as imazapic (e.g., Plateau) or sulfometuron (Oust XP or Spyder) can effectively control stiltgrass and prevent seed germination (Table 2). Treatments can be applied from early in the growing season through mid-summer. These treatments have been shown to effectively control populations but can also eradicate desirable plants and delay their re-establishment.
Selective grass-specific herbicides, such as sethoxydim, have also been effective at controlling stiltgrass (Table 1). The process of photosynthesis in grasses is slightly different than in non-grasses. This makes most grasses susceptible to some herbicides that will not harm other plants. In many cases, stiltgrass is the only susceptible grass that is found in shaded environments, allowing managers to target it without damaging or preventing the germination of desirable, native plants. Additional applications may be needed in subsequent years to control newly established plants that emerge from the seed bank. Numerous other grass-specific herbicides can be effective against stiltgrass. However, most are not labeled for use and are illegal to use in woodland areas.
Disclaimer
Label recommendations should be followed closely to maximize the potential for successful control and to ensure safe use. Mixing and application instructions on the label supersede any instructions provided in this fact sheet. Treated sites should be monitored annually to determine whether control is achieved and to detect re-infestation. Herbicides are approved for specific uses by the U.S. Environmental Protection Agency. Only uses and application methods that are listed and described on the pesticide's label are allowable. The herbicides listed in this fact sheet were appropriately labeled at the time of publication. Because pesticide labeling can change at any time, you should verify that a particular herbicide is currently labeled for your intended use. At the time of this writing, current labels and Safety Data Sheets (SDS) for herbicides discussed in this publication were on the Crop Data Management Systems website (cdms.net/).
The documentation displayed below can also be acquired from the herbicide manufacturers.
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References
Kleczewski, N., Flory, S.L., & Nice, G. (2011). An introduction to Microstegium vimineum (Japanese stiltgrass/Nepalese browntop) and emerging invasive grass in the eastern United States. Purdue Extension Weed Science, Indiana University Department of Biology.
florylab.com/wp-content/uploads/2022/12/Kleczewski-Flory-and-Nice-Mv-Purdue-info-sheet.pdf
Landschoot, P., Delvalle, T., & Abbey, T. (2020). Lawn and Turfgrass Weeds: Japanese Stiltgrass [Microstegium vimineum (Trin.) A. Camus]. Penn State Extension, The Pennsylvania State University.
extension.psu.edu/lawn-and-turfgrass-weeds-japanese-stiltgrass-microstegium-vimineum-trin-a-camus
Leicht, S.A., Silander Jr., J.A., & Greenwood, K. (2005). Assessing the competitive ability of Japanese stiltgrass, Microstegium vimineum. (Trin.) A. Camus. The Journal of the Torrey Botanical Society, 132(4),573–580.
doi.org/10.3159/1095-5674(2005)132[573:ATCAOJ]2.0.CO;2
McGill, D.W., Grafton, W.N., & Pomp, J.A. (2008). Managing Japanese Stiltgrass Dominated Communities in the Ridge and Valley Physiographic Province in Eastern West Virginia. In Jacobs, D. F., & Michler, C. H., Proceedings 16th Central Hardwoods Forest Conference (pp. 483–490). United States Department of Agriculture.
fs.usda.gov/nrs/pubs/gtr/gtr_nrs-p-24.pdf
Neal, J.C., & Judge, C.A. (2023). Japanese Stiltgrass Identification and Management. Horticulture Information Leaflets. NC State Extension.
content.ces.ncsu.edu/japanese-stiltgrass-identification-and-management#:~:text=Brief%20Description&text=Japanese%20stiltgrass%20(also%20known%20as,Figure%201.%20Japanese%20stiltgrass%20habit
Swearingen, J.M., & Adams, S. (2008). Fact Sheet: Japanese Stiltgrass. Plant Conservation Alliance's Alien Plant Working Group. National Park Service.
invasive.org/alien/fact/pdf/mivi1.pdf
Originally written Aug. 22, 2011, by David K. Apsley, Natural Resources Specialist, School of Environment and Natural Resources, Ohio State University Extension; and Annemarie Smith, Invasive Species Forester, Division of Forestry, Ohio Department of Natural Resources.