Microstegium vimineum (Japanese stiltgrass)

This invasive sprawling annual grass is a huge issue across WNC. Known as a voracious seeder (a single plant can disperse over 1,000 viable seeds), Japanese stiltgrass is a perennial challenge throughout WNC. First introduced in 1919 to the United States, it was brought from China originally as packing material. Today, it is commonly found on streambanks particularly in shaded moist areas but it can also be found in a wide variety of settings due to its adaptability. Disturbed sites due to flooding and disturbance in woodland areas can make prime habitat for Japanese stiltgrass to spread.

Ecologically, Japanese stiltgrass can displace much of the understory forest floor native vegetation due to its aggressive seeding ability as well as having the ability to root at the node. Germination is seen in the early spring, with flower initiation beginning in late July, with mature flowers, having self-fertile seed, being borne September through October.

Identification:

It is imperative to identify Japanese stiltgrass as early as possible to prevent large populations from establishing in areas. Be on the lookout for erect patches of grass (up to 3’ tall if unmowed) with leaf blades that are entire, rolled in the bud, and often have a slightly off-center silver stripe down the mid-rib of the leaf. The leaves are sparsely hairy on the upper side of the leaf and nearly hairless on the underside of the leaf. Hairs will be found at the collar region of the leaf, as well as the margin of the sheath of the grass blade.

Silvery midrib present on Japanese stilt grass leaf.

Look-a-likes include whitegrass (Leersia virginica) which has leaves longer and thinner than stiltgrass without the silver stripe located in the midrib, wire grass (Muhlenbergia schereberi) with leaves much narrower than Japanese stiltgrass with more of a mat habit, and crabgrass (Digitaria spp.) which has flattened stems as well as flower spikes that are fingered in 2-9 fragments.

Control:

Mechanically, hand digging and physical removal can work on small patches. Importantly, plan to do this prior to flower maturation, otherwise hand removal could spread plant populations even more due to the movement of viable seed in the plant material. Mowing can be a good management tool to prevent seeding out in the fall, but it is imperative to mow after flowers initialize but before the flowers reach maturity. Mowing too early can lead to seed germination of more stiltgrass in the growing season that is present in the seed bank. Mowing too late can spread the seed as the mowing process is done. Typically this means mowing in late July or August for our area. Seeds of Japanese stiltgrass are referred to as being cleistogamous (self-fertilized before the flower opens) meaning that some florets will have viable seed before flowers are fully opened and seeds are dispersed. Timing of mowing and chemical treatment is critical to provide long-lasting control.

Chemically, tools are available to treat Japanese stiltgrass. Preemergence chemical control options include dithiopyr and indaziflam which are both specifically labeled for use for Japanese stiltgrass. Other products that are labeled for pre emergent control for crabgrass will also have activity for Japanese stiltgrass. It is important for the product to be applied at least 2 weeks before seed germination. In our area, seed germination of Japanese stiltgrass is typically in early spring (late February or early March).

In terms of post emergence chemical control options we have selective and non-selective herbicides available. Selective herbicides to be used in grasses to control Japanese stiltgrass include: clethodim, fenoxaprop or sethoxydim. Non-selective tools like glyphosate, or glufosinate (Finale) also provide good control. Generally the optimal time to spray for Japanese stiltgrass is early summer but control can be had if sprayed later (more than likely multiple sprays will be needed to achieve optimal control regardless of timing). There are no silver bullets in the control of tough invasive plants, but active and consistent management can lead to the reduction of populations over time. This is magnified as it relates to Japanese stiltgrass due to high densities of seed in the seed bank around established populations meaning that multiple years of control will be needed.

Be mindful of drift when using any herbicide product and always follow pesticide label directions! This is important to understand how to use a product safely, and where you can use that product. Note that in certain sites, like aquatic sites, right-of-way, or forested areas that products have to be specifically listed for use in those areas in order to utilize an herbicide. If you have questions about product recommendations or how to manage stiltgrass, always feel free to reach out to your local county Extension office to receive guidance. For more information about invasive weed management, visit our website and continue to learn more as invasive plant BOLO’s are published.

Resources:

Invasive Plant Management: Forming a Gameplan after Helene

Japanese Stiltgrass Identification and Management- NC State Extension

NC State Plant Toolbox- Japanese Stiltgrass

Japanese Stiltgrass- PSU Extension

Field Guide to the ID of Japanese Stiltgrass- Alabama Cooperative Extension