Beware Stiltgrass: now is the time!
Japanese stiltgrass (Microstegium vimineum). A faint silvery mid-leaf vein is one key to identification. (Blue Ridge PRISM)
It has delicate, bright green foliage and slender leaves with a silvery mid-vein. These features give Japanese stiltgrass a deceptively harmless appearance, but it is damaging to ecosystems up and down the East Coast! Even where the grass has been established for only a few years, it forms a dense ground cover that smothers native plants and prevents regeneration of forests and fields. Every plant can produce up to 1,000 seeds that are spread by animals, runoff, and even human foot traffic. Stiltgrass has no natural predators in our region; and one of its weapons is to release chemicals into the soil, changing soil chemistry and inhibiting the growth of other plants. It’s no wonder that stiltgrass out competes native wildflowers, shrubs and saplings destroying biodiversity and natural habitat for animals, birds, and insects.
Now is the time to identify and control this invasive grass before it sets seed and spreads!
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.
Japanese stiltgrass is a warm season, annual grass with shallow roots. The shallow roots make it easy (and delightful!) to pull up in small patches, such as found along the edges of your yard or garden. It flourishes in 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.
Identification
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.
Image above: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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: Mowing and weed-whacking can be effective to greatly reduce seed formation, but it has to be done only correctly. Mowing is best done just before flowering in August and September and needs be done only once if you wait until then. Cut stiltgrass as low as possible, scalping it the ground to remove all flowers. When using a string-trimmer, hold the trimmer at a slight downward angle, digging about a quarter inch into the soil. This should sever roots from stems. Leave the clippings in place from mowed or cut stiltgrass if seeds haven’t formed. Bag them for landfill disposal if seeds have formed (bag them if you are unsure).
Foliar Spray: Apply a recommended herbicide before stiltgrass flowers and the seeds set, usually around 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 and references:
-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 monitor and apply management techniques for a number of years. It is worth it!
-Try to get your neighbors on-board with eradication efforts! It will be more effective and labor-saving in the long run.
-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
. This dense mat is fuel for fire.
Photo: Ken Druse