Japanese Stiltgrass

A Pervasive Invasive

You may have noticed the floors of wooded areas in Appalachian forests being overtaken by dense overgrowth of a weedy grass. More than likely, the culprit is an invasive weed referred to as Japanese stiltgrass ( Microstegium vimineum). Japanese stiltgrass is considered to be native to eastern Asia and was introduced to North America during the early 1900s when it was used as packing material for imported porcelain shipments to Tennessee. It also grows in pastures or other disturbed sites, such as roadsides or power-line corridors, in proximity to wooded areas. Although the nutritional attributes of this grass are in the favorable range, it is not usually considered to be a palatable forage species by livestock.

Japanese stiltgrass can raise the pH of the soil where it grows, affecting the flora and fauna of invaded forest floors. It is capable of establishing dense canopies that can displace native species by excluding light, disrupting the regeneration and natural succession phenomena in timbered forests. This fast-growing weed also is starting to encroach on managed landscapes, such as home lawns and gardens. Being an annual, it propagates primarily through seeds, but it also is capable of spreading from its point of growth by rooting at its nodes.

Japanese Stiltgrass Identification

Japanese stiltgrass is a shallow-rooted, warm-season, annual grass that typically thrives in moist and shaded environments. Its leaves are lance-shaped and asymmetrical with a reflective midrib. The ligule, a structure at the base of the inner side of the leaf, of Japanese stiltgrass is short and membranous. It has a slender, wiry stem that can produce adventitious roots from lower nodes that come in contact with the soil. It typically grows to about knee-height, but it can grow up to 3 feet tall under ideal conditions.

Japanese stiltgrass comes to bloom by late summer. Seeds are borne on spikes and are usually dispersed by animals, such as deer, or moving surface water, but they also can be moved with heavy equipment or hay. The seeds of Japanese stiltgrass are capable of remaining viable in the soil for three to five years. Seeds start to germinate in early spring, anytime from late March to mid-April in West Virginia.

Controls for Japanese Stiltgrass

Control measures can be effective when targeted to newly infested areas with relatively small Japanese stiltgrass populations. In landscapes, applying a suitable mulch, such as wood chips or landscape fabric, prior to seed germination can be effective. The shallow root system makes hand removal an effective method to manage small populations. Bare soil must be kept covered because early removal may cause germination of remaining seeds in the exposed soil, which may complete another life cycle during the growing season. Mechanical methods, such as mowing, should be carried out before they come to bloom in late summer. In lawns or landscapes, however, where they are constantly mowed, the plants may adapt by blooming at low heights.

Applying a pre-emergent herbicide is effective in situations where such applications are feasible. Herbicides containing the active ingredient pendimethalin (Pendulum, Prowl H2O) are effective to control stiltgrass prior to germination. Actively growing stiltgrass may be selectively controlled by herbicides containing fenoxaprop (Acclaim Extra), sethoxydim (Poast, Vantage), clethodim (Select Max), quizalofop (Assure II) or fluazifop (Fusilade), which do not cause injury to broadleaf plants. Non-selective herbicides, such as glyphosate (Accord, Rodeo, Roundup) or glufosinate (Finale, Liberty, Rely), may be used to control stiltgrass when total weed control is desired. Post-emergent herbicides are most effective when applied prior to the bloom stage.

It can be challenging to manage extensive areas when taken over by Japanese stiltgrass. Although biological control agents are not currently available, a fungus belonging to the Bipolaris genus is known to cause varying levels of necrotic lesions and blight to its leaves. Monitoring a managed site free of stiltgrass for the three to five years after treatment may be essential to deplete the seedbank completely. This may be accomplished by reseeding and stabilizing the area with desirable native plants, along with repetitive removal of any residual stiltgrass before it comes to bloom.

Author:  Rakesh Chandran, WVU Extension Weed Science Specialist  
Last Reviewed: August 2020 

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