Stiltgrass: now is the time!

Japanese stiltgrass (Microstegium vimineum), James H. Miller, USDA Forest Service

Blue Ridge PRISM Recommendations

Now is the time to identify and control this invasive grass before it sets seed and spreads.

• Use the guide from Blue Ridge PRISM, reprinted below, to identify Japanese stiltgrass (Microstegium vimineum) in the landscape.

• For small patches, pull up plants by the root when the soil is moist. For larger areas, cut/mow as close to the ground as possible so that no green is left on the plant.

Japanese stiltgrass (Microstegium vimineum) was once used as packing material for transporting porcelain from Asia to North America. It was discovered in the wild in the United States in 1919, most likely due to seed being accidentally dropped outdoors. A single plant can produce up to 1,000 seeds that can remain viable in the soil for up to five years. The seeds are then spread by animals, rain runoff, soil, and even human foot traffic. Taking action now will help minimize seed production and prevent stiltgrass from achieving a wider footprint.

Silvery off-center stripe on leaf, Leslie J. Mehrhoff, University of Connecticut. Bugwood.org

Japanese stiltgrass is a warm season, annual grass with shallow roots. It is found across a variety of light and moisture conditions. Plant height varies from 6 inches to 4 feet tall depending upon the growing conditions. Stiltgrass grows tallest in moist and sunny environments. Taller plants will typically lie flat along the ground or propped up against other vegetation.

Stiltgrass has pale green, lance-shaped leaves that are between one to three inches long. The leaves alternate along an often droopy stem. Look for a silvery main vein running just off center of each leaf.

An inflorescence (flower) emerges in late summer, maturing to carry the small seeds. The spikes are 1 to 2 inches in length.

Timing is key when for using control measures of hand-pulling, mowing, or spraying.*

Image: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Timing is critical when using mechanical removal techniques to control Japanese stiltgrass. It is best to delay cutting/mowing until later in the summer to avoid regrowth during the season.

The best time to mow or cut stiltgrass is right as the inflorescence begins to appear but before it sets seed. In Virginia, now (August) is generally a good time to cut/mow.

*Keep in mind that the exact time will depend on the plant’s geographic location, soil moisture, and amount of sunlight the plant receives.

Roots and stems

The stems are thin and wiry and can often be interconnected by a runner stem. The stems are supported by small, stiltlike roots (thus the name). In winter, the stems can form a dense thatch over the soil.

Nancy Loewenstein, Auburn University. Bugwood.org

Hand-pull:  Small patches in garden beds or elsewhere can be easily hand-pulled because of Japanese stiltgrass' shallow root system. Pulling when the soil is moist will speed the process.

Mow:  For larger areas of stiltgrass, use a mower set very low and cut as close to the ground as possible so that no green is left on the plant. This decreases the chance of it resprouting. If using a string-trimmer, hold the trimmer at a slight downward angle so the string digs about a quarter-inch into the ground to sever roots from stems. Leave clippings from mowed or cut stiltgrass in place to die if seeds have not formed. Timing is key here. Mow when the plants are just about to flower, late July to August.

Foliar Spray:  Apply a recommended herbicide before stiltgrass flowers and sets seed, July - August. Grass-selective herbicides are most effective. See Virginia Department of Forestry Guidelines or A Management Guide for Invasive Plants in Southern Forests for specific herbicide recommendations.

Notes:
-Be aware that although you have eliminated this year’s seed production there is still seed in the soil that can germinate. As a result, you will need to employ monitoring and management techniques for a number of years. It is worth it!
-Always follow all herbicide label directions and wear personal protective equipment (PPE) per label instructions.
-Take care to avoid herbicide contact with desirable plants.
-For an in-depth discussion about Japanese stiltgrass and its control options, view Blue Ridge PRISM's video of our 2022 Summer Meeting:  "Simply Stiltgrass"

Thatch of dried stiltgrass stems covering ground in winter

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Chris Evans, University of Illinois. Bugwood.org