Japanese stiltgrass (Microstegium vimineum)was first discovered growing in North America in Tennessee in 1919. It is a member of the grass family (Poaceae) and also known as Nepalese browntop or Chinese packing grass. As the last moniker implies, the thatch of this species was once used to pack crates for shipment of goods across the sea. This use as a packing material is likely how this species was introduced to North America.
Life Cycle: Japanese stiltgrass is an annual warm-season grass. This means that it competes its entire life cycle in a single growing season and primarily grows during the warm summer months. It usually begins germination in April and will continue to germinate throughout the growing season if conditions allow. Flowering generally takes place in August or September within the region and is promptly followed by seed production. This species reproduces from seed and vegetatively through stolons, which are ground runners that will root at the nodes when in contact with soil.
Identification:
- Height: Generally, 1-4 feet. Has been observed reaching heights of up to 7 feet in southern Illinois. Due to the spindly nature of this plant, it usually needs other plants or brush to use as structure for achieving such size.
- Leaves: Asymmetrical, lance-shaped, and pale green, usually 1-3 inches long. There is a silver midrib down the middle of the leaf, which is the most important identifying feature for this plant.
- Flowers: Very small and discreet, in one or two terminal spikes.
- Look-alikes: Species within the Leersia and Polygonum may resemble Japanese stiltgrass. However, neither will have the tell-tail silver midrib that is the key identifying feature of stiltgrass
Japanese stiltgrass seedlings in early spring. (Photo by Nick Seaton)
Invasive Advantages: The primary characteristics that give Japanese stiltgrass an advantage over native plants are related to seed production, longevity, and dispersal. This species can produce up to 1,000 seeds per plant that can remain viable in the seedbank for 3-5 years. Given how densely this species can grow, a very large seedbank can be established that will require several years of diligent control to deplete. The seeds are very small and easily transported by moving water, footwear, clothing, pets, wildlife, and all types of machinery. Avoid recreating and working in infested areas during early fall months while seed is present. If this is not possible, inspect and remove seeds from footwear, clothing, pets, and equipment before leaving an infested site.
Habitat and Ecological Impacts: Japanese stiltgrass has a wide tolerance range and can be found in many habitats. In southern Illinois, it is commonly found in floodplains and riparian areas, on roadsides and along trails, in addition to open and closed forest systems. It thrives in disturbed areas, where bare mineral soil and/or an abundance of sunlight are available. Though full-sun conditions maximize growth and seed production, this species can persist in full shade.
Due to the ability of this species to spread and reproduce, Japanese stiltgrass can quickly establish dominance in an ecosystem, especially following disturbance events. Prolonged infestation displaces native plants and degrades habitat, impacting species richness and abundance of both flora and fauna. Long-term effects also include changes in species composition as Japanese stiltgrass infestations can inhibit the regeneration of heavy-seed tree species like oak and hickory.
Control: There are several ways to control Japanese stiltgrass. However, the most effective treatment plans include a combination of the following treatments, or multiple treatments within a single growing season. Due to the longevity of the seedbank associated with this species, several years of thorough treatment are necessary to produce meaningful results.
Foliar application of herbicide with an electric pump system mounted on an ATV. (Photo by Nathan Speagle)
- Mechanical treatments involve hand pulling and mowing. The small and shallow roots of this species make hand pulling a simple task. However, this method is often the most labor intensive and is not recommended for large infestations. Cease hand pulling when flowering begins to prevent spreading seed.
Mowing can be effective at eliminating or at least reducing seed production, if properly timed. The ideal timing for mowing is in the late summer, right before flowering. Mowing too early will result in regrowth and seed production, while mowing too late can spread seed.
- Chemical treatments involve using foliar applications of herbicide on Japanese stiltgrass before flowering occurs. It is recommended to wait until plants are 6-8 inches before spraying, this generally occurs in late spring. Multiple treatments of the same infestation may be required in a single growing season as seeds will continue to germinate throughout the growing season. Several herbicides are effective in treating this species, but some are more advantageous than others.
Sethoxydim and clethodim are grass-specific herbicides, meaning they will not harm broadleaf plants. Both herbicides provide effective control while minimizing collateral damage to non-target plants. Perennial grasses will usually survive mild exposure to these herbicides.
Glyphosate is also an effective option for treating Japanese stiltgrass, but since it is a broad-spectrum herbicide it has the ability to kill all plants with which it comes into contact. If treating infestations of Japanese stiltgrass interspersed with other invasives and the potential for damage to native species is low, this may be a good option. Another scenario for glyphosate is using a formulation approved for aquatic use (Aquaneat, Rodeo, ShoreKlear) to treat infestations on the banks of streams, rivers, ponds and lakes, or on sand bars within a waterway. If using herbicides approved for aquatic use, please read the herbicide label and follow all best management practices.
Japanese stiltgrass thatch along a dormant field edge in Jackson County, Illinois. (Photo by Nathan Speagle)