Peter H. Dernoeden, Ph. D

The Origins of Japanese Stiltgrass

Japanese stiltgrass (Microstegium vimineum) is also known as Japanese grass and Napalese browntop.

It is a warm-season annual that germinates in early spring, a few weeks prior to the time that crabgrass and yellow foxtail emerge.

In non-mown areas it grows tall, produces seedheads in late summer-early autumn and eventually is killed after several frosts. It is a non-native, invasive plant believed to have been introduced from Japan as a packing material. Japanese stiltgrass is found in most states east of the Mississippi River.

Visual Appearance and Identification in Early Spring

Seedlings emerge in early spring about 2 to 3 weeks prior (i.e., about mid- March in our region) to crabgrass and yellow foxtail. Unlike crabgrass and foxtail, Japanese stiltgrass seedling leaves are broad-textured and rounded, and stiltgrass plants are mostly found in shade or partially shaded sites. Leaves are sparsely hairy and the ligule is short, membranous, and the collar region is hairy.

Due to its upright growth, identification is made easier in non-mowed or non-turf sites by June.

In non-mowed areas, plants grow from 1 to 3 feet or higher in a branching and sprawling manner. Spreading stems climb over other vegetation, and stems that become prostrate can root at nodes. Given its fibrous root system, plants are easily pulled out of the ground. Under mowing, Japanese stiltgrass develops in prostrate clumps that look like clusters of coarse-textured crabgrass plants.

Where Japanese Stiltgrass is found and How it Spreads

Japanese stiltgrass was first recognized as a problem in woodlands and along stream banks in southeastern and mid-Atlantic States. It is uncommon in coastal plain areas of the Delmarva Peninsula versus areas west of the Chesapeake Bay. Within the last 15 years, it has spread to lower maintenance turfgrass sites, including tree-lined roughs and lawns as well as ornamental beds.

While most common in wet and shaded areas, Japanese stiltgrass sometimes can be found on sunny, exposed slopes where soil has been disturbed.

Stiltgrass rapidly spreads and can out-compete turf and other vegetation. It tolerates mowing and spreads, forming clumps of coarse-textured plants usually in shaded tree or hedge lines.

Seedhead and Leaf Appearance of Stiltgrass

Japanese stiltgrass leaves alternate along a central branch resembling small bamboo. Leaves are wider and more elliptical (i.e., longer than wide) versus crabgrass or foxtail, and taper at each end. There is a stripe of whitish hairs arranged along the midrib of the upper leaf surface. Seedheads do not appear until late September or October.

Seedheads are tall without mowing and stems are fine textured and turn tan with age. Seeds form on 1 to 3 finger-like spikelets, which grow from tips of slender seed stalks. Since each plant can produce large numbers of seed, it is imperative that plants be controlled before seed production begins. Seed can live up to seven years in soil (Neal and Judge, 2013), and thus a large seed-bank will ensure no end to the problem in the absence of an aggressive control program.

Upright plants growing in shaded roughs turn a purplish-red color when damaged by a few frosts. Prostrate plants under mowing turn brown following a few frosts.

Dead plants persist throughout winter and into early summer, when new seedlings emerge and begin to sprawl and cover the dead stiltgrass vegetation produced in the previous year.

Pre-emergence Solutions and Control of Stiltgrass

Since each plant can produce prodigious numbers of seed, which can persist in soils for several years, it is prudent to target stiltgrass before flowers and subsequent seed appear in September.

Use of a pre-emergence herbicide is the most effective and economical approach to controlling stiltgrass.

Pre-emergence herbicides shown to provide a significant level (i.e., don’t expect >85%) included Barricade (prodiamine), Dimension (dithiopyr), Pendulum (pendimethalin) and RonStar (oxadiazon) (Neal and Judge, 2013). These herbicides must be applied between mid-February and mid-March in our region, since stiltgrass emerges several weeks prior to crabgrass (i.e., crabgrass usually emerges early-to-mid- April in our region).

When Japanese stiltgrass growth is in the 3 leaf - 3 tiller stage, it can be effectively controlled post-emergence with Acclaim Extra (fenoxaprop-ethyl). Drive (quinclorac) and MSMA were shown to be ineffective (Neal and Judge, 2013).

Once plants begin to spread forming mats or a sprawling growth, it is not likely that Acclaim will be effective.

Homeowner and Personal Control of Japanese Stiltgrass

Plants developing in small, isolated pockets should be hand-pulled.

Once plants are numerous, tall and sprawling, a non-selective herbicide such as Round-up (glyphosate) or Finale (glufosinate) should be considered. Careful spraying of an aforementioned non-selective in low water volumes to ensure that herbicide does not drip down to contact turf or ornamentals, can go a long way in reducing invasiveness as well as significantly reduce seed production.

For homeowners, a non-selective herbicide mixed with water in a small spray/pump bottle (like Windex-type pump bottles) would deliver a light spray to sprawling foliage without dripping downward to injure underlying turf or ornamentals.

Battling established pockets of Japanese stiltgrass becomes a war of attrition.

While labor intensive, professionals need to combine use of a pre-emergence herbicide application in late winter with use of Acclaim where necessary.

In some situations, vigilant hand-pulling and the careful placement of a non-selective herbicide to sprawling stiltgrass foliage is advised to limit invasiveness and seed production.

Reference: Neal, J. and C. Judge. 2013. Japanese Stiltgrass Identification and Management. North Carolina State University Extension Horticulture Leaflet.