Common Name: Japanese stilt grass, Nepalese browntopAuthor: Joshua Simpson
Scientific Name: Microstegium vimineum
Classification: Photos: Taken from The Nature Conservancy
Phylum or Division: Magnoliophyta
Identification: Microstegium vimineum is an annual C-4 shade tolerant grass that can spread by adventitious roots arising at nodes when lying decumbant. Lanceolate leaves are pale green, 5-8 cm long, slightly pubescent on top and bottom, and have a distinct shiny midrib. Flowering racemes can arise as single or sets of two or three. Spikelets are paired, upper spikelet is fertile while lower spikelet is infertile. The fruit is a caryopsis that can vary from yellow to red in color. The plant can grow between 24-40 inches in height.
Original Distribution: Microstegium vimineum has a broad native range throughout East Asia. It is native to China, Japan, Korea, Nepal, Malaysia, Ryukyus, and India.
Current Distribution: In the United States, current distribution has been reported from New York to Florida, and West to Illinois and Texas. It has also been reported in Puerto Rico.
Site and Date of Introduction: The initial discovery was reported in Knoxville, Tennessee in 1919. Other early reports include; 1931 in Virginia, 1933 in North Carolina, 1934 in Alabama, 1938 in both Kentucky and Pennsylvania. Spread has continued at a steady pace. Later found in Branford, Connecticut, 1984. Then in Hamden County, Massachusetts in 1998.
Mode(s) of Introduction: In the early 1900's grasses were used as a cheap, light-weight packing material for fragile items. M. vimineum was one such grass used for this purpose, including fine China porcelain which is the most likely route of introduction, coming from Eastern China. Although the culms of the plant have been used for basket weaving, there are no reports of intentional cultivation.
Reason(s) Why it has Become Established: M. vimineum has several traits typical of invasive species that contribute to its success. First, it is able to germinate quickly and flourish in disturbed areas, these can be human disturbances such as, roadsides or ditch banks, but the disturbance can also be natural like, flood plains and stream sides. This grass is not only able to grow rapidly, but can grow in a diverse variety of light exposure; developing and flowering with as little as 5% light exposure. This allows it to invade forest understory habitat. It has abundant seed production (up to 1000 seeds per individual), creating an extensive seed bank. The seeds are small. light, and able to float. This facilitates wide spread seed dispersal in wetland and flood areas. Seeds are primarily spread by water, but also known to be spread by attaching to animals and humans, so distribution into human disturbed sites is favorable. If plants are destroyed in early to mid summer, a new cohort of seeds can rapidly germinate and mature at a faster rate, thus still producing seed for that growing year. This illustrates how persistent the plant can be.
Ecological Role: Microstegium vimineum does best in wet areas where water provides the primary dispersal mechanism. It flourishes on floodplains, and flood scoured banks of waterways (i.e. stream, ditch, canal). It can also be found on wetland edges, in damp fields, or well watered lawns. Stilt grass is also found colonizing forest edges, roadsides, and along trails. It is very shade tolerant, but can also prosper in nearly full sunlight. Plants have been found at up to 4,000 ft in elevation and occur in areas that reach -5 degrees fahrenheit in the winter (though they are not alive during that season). This ground cover species has been shown to change the pH of the soil as well as changing the organic soil and litter ratios.
Benefit(s): This species has very little wildlife food value. Besides historical uses, as a packing material and basket weaving, no other direct benefits are known. Because it germinates quickly on bare soil, it may play a short term role in soil stabilization.
Threat(s): Stilt grass is a threat to biodiversity and natural ecosystems. Once established, this grass is able to spread quickly and replace native communities, eventually creating monoculture stands. Through an alteration of natural soil conditions it hinders new growth of native vegetation. Its high shade tolerance allows it to invade lightly disturbed forest understory, unlike many other invasive species. The abundant seed production and extensive seed bank allows this species to persist over a long period of time, and potentially unfavorable years. They also create an indirect threat to native species, for example, this is not a favorable forage species, so where grazers are present they will preferably select the native species before stilt grass, if they choose to forage on stilt grass at all.
Control Level Diagnosis: Medium-high priority. Microstegium vimineum has spread throughout the eastern United States and continues to expand its range. It establishes quickly in disturbed areas, but is effectively kept at bay in undisturbed areas. Although the bigger threat comes once established, it can then quickly dominate, so quick control is important.
Control Method: Prevention of spread is the best control method. But where plants have already become established fast action is beneficial for effective control. Small populations can be controlled manually since roots are shallow and plants can be pulled up fairly easy. This would have limited impact to the surrounding habitat. For slightly larger areas of invasion mechanical methods can be used, either mowing or weed whacking. But seasonal timing is very important as well, any control method should be applied or conducted in late August to early September when plants are late in flowering stage but have not started to set seed. If plants are removed too early new seeds will germinate quickly and can mature rapidly.
Chemical control: For more extensive invasions chemical means are necessary because manual methods would be too overwhelming and time consuming. Chemical treatment should also be applied late in the season and can be more effective if mowed prior to application. The herbicide Imazameth is the best option for controlling stilt grass because it allows the native broad leaved plants to revegetate the treated area. Treatment with Imazameth requires 6 ounces per acre. Sethoxydin applied at a 1.5% solution mixed with water and a 1% nonphytotoxic vegetable-based oil can also provide excellent control. Sethydoxin also kills grasses without causing damage to the dicot species. Glyphosate can also be used, but would be more ideal in monotypic stands because it results in death of all plants. This may actually contribute to stilt grass becoming dominant, if monitoring and treatment is not applied the following year. There are also glyphosate formula's designed for wetland areas (Rodeo). Glyphosate should be applied at a 2% solution with water and a 0.5% surfacant. All herbicides should be sprayed to thoroughly wet the surface of the plants, but should not be sprayed to the point of run-off. Herbicides should not be applied when rain is expected within two hours. Ambient air temperature should also be above 65 degrees Fahrenheit for better transport of herbicide to the root system.
No biological controls have been found effective. Grazing is not an option either; cattle, deer, and even goats avoid feeding on it.
Flooding has been found to work, but needs to be fairly constant over a three month period for mature plants and ten weeks for seeds. Seeds have been shown to germinate under water, but plants cannot survive. If water is removed too soon more seeds will germinate. This is not a realistic method over large areas and would be best applied to monoculture stands due to intense ecological effects and negative impacts on other species.
Prescribed burns in the Spring are ineffective, because of large seed banks. Thus far, fall burns have not proven to be very effective either.
No matter which control method is used, it is necessary to follow up and monitor in successive years due to the large seed bank. Seeds remain viable in the soil for up to five years.References
1. Swearingen, J.M. Alien Plant Working Group. Japanese Stilt Grass (Microstegium vimineum). http://www.nps.gov/plants/alien/fact/mivi1.htm (Nov. 6, 2004).
2. Tu, M. The Nature Conservancy’s Wildland Invasive Species Program. Element Stewardship Abstract for Microstegium vimineum. http://tncweeds.ucdavis.edu/esadocs/micvimi.html (Nov. 6, 2004).
3. Cole, P.G. and Weltzin, J.F. Environmental Correlates of the Distribution and Abundance of Microstegium vimineum, in
East Tennessee. Southeastern Naturalist. 3(3):545-562. 2004.
4. IPANE; Invasive Plant Atlas of New England. Microstegium vimineum (Japanese stilit grass). http://webapps.lib.uconn.edu/ipane/browsing.cfm?descriptionid=12 (Nov. 21, 2004).
5. Invasive plants of the Eastern United States. Nepalese Browntop. http://www.invasive.org/eastern/srs/NB.html (Oct. 20, 2004).
6. Fairbrothers, D.E. and Gray, J.R. Microstegium vimineum (Trin.) A. Camus (Gramineae) in the United States. Bulletin of the Torrey Botanical Club 99:97-100. 1972.
7. Barden, L.S. Invasion of Microstegium vimineum (Poaceae), an Exotic, Annual, Shade Tolerant, C-4 Grass, into a North Carolina Floodplain. American Midland Naturalist. 118:40-45. 1987.
8. The Nature Conservancy. Invasive Species Initiative. http://tncweeds.ucdavis.edu/esadocs/micrvimi.html (Nov. 24, 2004)