by Andrea Laine, EMGV
Typically I don’t get riled up about weeds that are easy to pull up by hand, but Japanese stiltgrass (Microstegium vimineum) is a HUGE exception. Despite its fibrous, shallow root system, in just three to five years this invasive species can overtake a natural area, pushing out natives and non-natives alike. It is also detrimental to ground-nesting birds and can contribute to fueling forest fires. I’ve observed more and more of it in local forests and parks where I hike as well as the roadsides in my woodsy Durham County neighborhood. It’s a sad sight, especially on conservation lands.
This spring was the first time I noticed stiltgrass at a friend’s home in the Piedmont region of Virginia. Normally when I‘m there I’m grousing about periwinkle (Vinca minor) and winged burning bush (Euonymous alata), two other invasive species which I have previously blogged about. I admit to feeling a bit of poetic justice at the sight of the one invasive (periwinkle) being overtaken by another (stiltgrass). But the feeling was fleeting. Every subsequent feeling has been more along battle lines – how can I fight this?
Identification
Before attempting to eradicate any weed, you want to be sure you have identified it correctly. When I first noticed stiltgrass, its structure and wispiness reminded me of bamboo, albeit a tiny version.
In plant ID lingo stiltgrass is a “prostrate to erect, sprawling and freely branched summer annual with spreading stems that root at the nodes … Leaves are rolled in the bud; ligules are short membranous with hairs …”1 If you’re thinking, hey what IS a ligule? Don’t despair! Stiltgrass does have one distinguishing characteristic that you need not be a botanist to recognize: Each leaf on stiltgrass has a silvery midvein that divides the leaf unevenly.
Note in the accompanying photo gallery how this feature is absent from other plants (some weedy, some not) that are often mistaken for stiltgrass.
The root structure of stiltgrass is also distinct from other weeds often mistaken for stiltgrass as noted in these photos. (Stiltgrass is the photo with the brown background.)
unidentified weed 
Stiltgrass
Growth habit and lifecycle
Japanese stiltgrass seeds germinate in early spring. The plants grow and strengthen through the summer. In June the Virginia patch was about six inches high; At the beginning of August, the plants were two to three feet tall. In NC it flowers from mid-September through October and soon after flowering the seeds are dispersed – 1000 seeds per one wispy plant! Seeds stay viable in the soil for four years.
I consulted a lot of sources before writing this post and it seems that there is not one “right place” for stiltgrass to thrive. Some sources advised sun, others shade. Some moist woodland, others dry roadsides. Apparently, it is adaptable to a variety of conditions. It will even tolerate a mild frost. And, it really makes its presence known in areas where the soil has been disturbed. This may have been a factor for the Virginia property I referred to earlier as several very large trees were felled, cut up, and carted away from the land over the last year. That kind of activity definitely disturbs soil and surrounding environment.
Understanding the lifecycle of a weed or any unwanted plant is important because in order to stop it from spreading you need to stop it before it seeds. The flowerhead on stiltgrass though is quite small as are the seeds, so best to act based on the time of year than on a visual. From now through September is a good time for those of us in Durham County to act.
Tactical solutions
Here are three ways to combat a stiltgrass invasion. Which tactic you choose will depend upon how much stiltgrass you have, where it is growing, and your comfort level with chemicals.
Hand-pulling or digging
While this tactic is typically my go-to for weeding, it only makes sense with small infestations and even then, there are some caveats. When we pull weeds by hand, we disturb the soil which is often enough to bring previously dormant seeds to the surface where they will receive the sunlight they need to germinate. “Hand-pulling of stiltgrass plants needs to be repeated and continued for many seasons until the seed bank is exhausted.“2
Mowing
If stiltgrass is growing in your lawn (or what passes as your lawn) then mowing seems like an obvious tactic. But when stiltgrass is mowed too early in its lifecycle, the roots re-energize and send new shoots above ground more quickly than the first time and it may flower and seed earlier, too.3 If possible, delay mowing stiltgrass until the end of August to deter regrowth or seeding.
The best way to prevent stiltgrass in a lawn is to follow best practices for lawn seeding and care. To learn how to properly maintain your lawn consult Carolina Lawns: A Guide to Maintaining Quality Turf in the Landscape
Herbicide
My friend has given me complete freedom to attack the burning bush and the stiltgrass around his home, but not the periwinkle which he likes very much. After three decades it is as much a part of his mountain retreat as the cabin it surrounds. Knowing I needed to save the periwinkle, I turned to the one-percent solution. This is a tip I received from a weed control expert at a local botanical garden during an educational class. (We master gardeners need to complete at least eight hours of education each year.) Extension programs also endorse this solution.
A half to one-percent solution of glyphosate will kill Japanese stiltgrass without harming the other plants around it. Ready to spray containers of glyphosate I have purchased held an 8% solution. Concentrated varieties were 18%. I share this information to drive home the point that more IS NOT better. I suited up (long pants, long-sleeved shirt, tall rubber boots, nitrile gloves) before mixing up a much diluted version of the herbicide and I sprayed the stiltgrass.
Do not use glyphosate on your lawn. Pre-emergent herbicides for crabgrass are recommended for preventing stiltgrass from growing in a lawn. These are best applied in late spring or early summer so that the lawn has time to recover.
Weeding is a commitment
Whichever method you choose, plan on at least a five-year commitment. Since I don’t live on or near the property I treated, I won’t know the outcome of my effort until the fall. But I already understand that my work is not finished. I was working in a natural area on a mountain side. I could not reach all the stiltgrass. Hopefully, the patch of stiltgrass growing on your land is smaller, more easily accessible and responds to your chosen method of treatment.
Footnotes
1 and 2 – Detail about the identifying characteristics of stiltgrass and list of herbicides specifically labeled for stiltgrass: https://content.ces.ncsu.edu/japanese-stiltgrass-identification-and-management#
3 – Control options for grasses and grass-like plants: https://www.invasive.org/alien/pubs/midatlantic/control-grassesandsedges.htm
Additional Resources & Further Reading
Carolina Lawns: A Guide to Maintaining Quality Turf in the Landscape
https://content.ces.ncsu.edu/carolina-lawns
A very good weed key:
https://weedid.missouri.edu/weedinfo.cfm?weed_id=173
Invasive Plant Species Management, Quick Sheet 4: Japanese stiltgrass, Penn State
Invasive Weeds of the Appalachian Region, University of Tennessee Institute of Agriculture.