Although tedious, hand pulling is the most straightforward and effective solution for removing Japanese Stiltgrass, since it pulls up fairly easily compared to most weeds due to small root systems. Yes, you can repeatedly cut it back as an alternative, but unless you can cut it at the soil level, Stiltgrass tolerates low "mowing" well and may still produce seed heads if kept short from periodic trimming alone. Although certain pre-emergent herbicides can help prevent it from returning from seed in future springs, most of Montgomery County prohibits non-organic herbicides on home lawns, and for any Stiltgrass in wooded unmanaged areas we would not recommend treating with a pesticide. Deer are thought to be one of the main ways Stiltgrass seeds are introduced to new areas (or re-introduced, via their feet/legs transporting seeds), so having a barrier to deer entering the yard, if applicable and feasible, might be one additional way to reduce the chances of its return once it's eradicated.

Miri

Thanks Miri, I have pulled the small clumps all in my yard. Is this a good time to pull or next year wait until further into august? 

Hello Mark,

Anytime should be good to pull -- especially right after a good rain so the ground is softer -- but just get them before they go to seed. Generally, the earlier in its life cycle a weed can be removed, the better. Clearing a larger section may not impact much long-term but it certainly wouldn't hurt, both now and for the future if you intend to mulch or plant other species to try to keep the Stiltgrass spread at bay.

Japanese Stiltgrass is invasive and has colonized natural areas in the entire state, so it's unlikely any county or municipality is actively trying to manage it since it's unfortunately a fairly lost cause as this point, especially with the regional over-abundance of deer. Removal would be somewhat impractical without the installation of native plants to fill those cleared areas in, or at least without ongoing weed management to keep other opportunistic invasive species out. Since we would not recommend the use of an herbicide in a natural area, the only options to combat it are manual physical removal or repeated low trimming/mowing to keep them from forming seeds. Neither is probably very practical given this situation and the size of the area involved, but there won't be an easy way to keep it from re-invading the yard every year as seedlings germinate unless you were allowed to use a pre-emergent herbicide on the lawn to kill those germinating seeds.

If an area is cleared any time of year, or fallow during winter due to the natural dieback of these weeds, you could try mulching to suppress germination or other weed growth. Arborist wood chip mulch is a relatively low-cost resource that will also benefit the soil as it degrades. Wood chips are delivered by the dumptruck-load from tree removal companies and tend to be nearly free (maybe with a delivery fee) compared to the price of an equivalent amount of bark mulch. Wood chip mulch can also be laid a bit thicker than conventional bark mulches without suffocating tree roots, which helps to maintain weed suppression.

Another option may be to plant a native but aggressive species (or several, in a mix) along that border so they could out-compete some of the Stiltgrass. Granted, given the site conditions, they would need to be less palatable to deer while also being able to thrive in woodland conditions (part shade to mostly shade). Some examples of aggressive native spreaders (either via creeping or self-seeding) include Hayscented Fern, Sensitive Fern, Golden Ragwort, Summersweet (if the soil isn't too dry), Blue Mistflower, Orange Jewelweed, and White Wood Aster.

Miri

Thanks, since the Japanese Stilgrass dies off in the winter, isn't the answer to pull as much existing stiltgrass from the yard and simply use an approved pre-emergent EVERY spring ?

If your municipality allows a pre-emergent to be used on the lawn (almost all of Montgomery County prohibits non-organic lawn herbicide use, which essentially rules-out just about every highly-effective pre-emergent), then yes, it could and perhaps would need to be applied yearly in spring. (Probably twice each spring, spaced a few weeks apart.) The seed bank in the lawn itself would probably exhaust itself if Stiltgrass plants in the lawn were removed/cut before going to seed, but since deer or other factors could still move seed from the woods next to the yard into the lawn again, repeat eradication efforts would then be needed yearly. The alternative would be either management via herbicides or converting a zone of yard from lawn to garden beds as a buffer (since garden beds can be treated in Montgomery County) between the woods edge and the rest of the lawn.

Miri

Hello, we chatted a while back about japanese stiltgrass and I was speaking with Miri. I see that my concerns were published on the web.

Yes, all questions whose settings are left as public (the default selection when a submission form is filled-out) will be archived on the web, in Ask Extension's nationwide database. If you prefer it not be posted, you can change your question settings to private at any time; if you don't seem to have that option or can't find a way to change that setting, we can switch it to private for you.

Pulling the Stiltgrass out removes the whole plant, roots and all, so any time is fine because it can't regrow when it's completely removed. (Unlike perennial weeds like Canada Thistle which will snap off at the rhizome instead, and the rhizome left behind will resprout.) Cutting the Stiltgrass down with a mower will sometimes allow it to regrow since the roots and lower few inches of foliage remain, though doing so just prior to bloom or seed set is the timing most likely to be successful in terms of having it not regrow much or have enough time to set seed again before frost. Cutting it back to soil level with a weed-whacker might be more successful in that regard, since it removes more of the plant overall. And yes, regardless of removal method, getting it done before seeds mature and shed is best, though wildlife like deer (and maybe rabbits) could always re-introduce new seeds to an area if the space isn't fenced to exclude them.

Miri

Thanks how do I know that by pulling it will remove all the roots ? Should I wet the area with water first if it does not rain ?

Moist soil can make weeding easier, so maybe waiting for the hurricane remnant rains to pass through this week/weekend might be best. Stiltgrass tends to be easy to pull up with enough roots, so any small root fragments that might break off in the process and remain in the soil will be too inconsequential to generate new plants.

Seed production can depend on various environmental factors, though fortunately flower heads (the same stalks seeds will develop on) should be easy to see. Maryland Biodiversity Project data for Stiltgrass fruits/seeds shows that observations have been made beginning in early September (this is state-wide data, but can't be filtered to specific counties). In years with early-season hot weather, as we've had this year, that might advance plant growth stages by a couple weeks, and microclimate (conditions specific to very small areas) will also influence when individual populations start going to seed, so we can't really predict that event with more accuracy.

Miri

Miri- Thank you very much for your response. I saw the data and the graphs and that is very helpful.

It will probably dry out and die off pretty easily, but you can always temporarily bag it or put the debris pile on a tarp or something to dry out on a warm, sunny day or two first. If it hasn't gone to seed yet, this is the simplest approach, but if it has, either trash them or try to cut the seeds off (for the trash) before composting or sending the rest off for yard waste collection. Honestly, it's such a widespread weed that any seeds accidentally winding-up in yard waste collection anyway will not contribute much to the plant's spread, but it's best to avoid it if possible. Re-rooting after being pulled up is unlikely, especially if it dries out for a half-day or so bare-root. Unfortunately, we are not familiar with any tools used to make the hand removal job any faster/easier.

Miri

Thanks, what would happen if you cover the live stiltgrass with leaves, will it still drop seeds or die from lack of sun etc ?

We do not have research data regarding how easily the plant succumbs to smothering, but it would probably take more than a layer of leaf litter; a tarp or something more solidly light-blocking would be more impactful. How long it would take to starve-out covered mature Stiltgrass is hard to guess, but it might be several weeks. Regardless of how the grass dies (human-mediated or natural), it will shed seeds once the seeds are ripe. What's in question, and what we don't have a solid answer for, is how rapidly they will ripen and release once the flowers are pollinated. (Grasses are wind-pollinated, so they don't rely on insects.) Even already-dead plants can release viable seeds if the seeds had time to mature before the plant (or its above-ground parts, for perennials) died fully. Some plant seeds can even finish maturing if they are far enough along in development by the time the rest of the plant withers and dies, though we don't know if Stiltgrass falls into this category.

Miri

Hello, can you also tell me 

Hello Miri, I wanted to share pics of the Japanese stiltgrass that I recently hand pulled this week. I don’t see any seeds on them so this is what it looks like and also a picture of the roots.

Agreed, we do not see seed heads in the photos you sent, with the caveat that some can be hard to notice (refer to the video below). Any way you can prevent it from going to seed will be fine, whether that's repeated mowing or pulling it up. Some Stiltgrass can develop flowers and seeds fairly low to the ground since they tolerate mowing, which is why removal of the plant, while more tedious, will be more effective. Still, low mowing will at least reduce the amount of seed a plant can produce.

Some of the resource we've linked to previously show the seed heads, and we'll include them and others here for you to explore:

• Maryland Biodiversity Project -- Japanese Stiltgrass gallery (includes images of flowers and seed heads)
• UMD -- Japanese Stiltgrass in Home Landscapes (one photo in the gallery shows seeds developing)
• NC State -- image of Japanese Stiltgrass seed head
• Illinois Extension video (near the bottom of the page) -- the section on Japanese Stiltgrass runs from time 35:38 to 42:14

Miri

Thank you, one more question if I trimmed the stiltgrass with a weed trimmer so the leaves are gone how long does it take to grow back leaves ? How about if I trim it all the way down to the Earth ?

How quickly something grows back will depend on the situation, (moisture, heat, etc.) but now that you know what the 'flowers"/inflorescences on which the seeds are eventually produced, you can keep an eye on it.  
(I live near where Carroll, Frederick and Howard Counties converge and my Japanese Stiltgrass is just starting to bloom.)

We don't have research on it yet, but there are some public gardens that are having some luck with waiting until  Japanese Stiltgrass plants are just starting to bloom and then weed-whacking them down low so the seed can't mature or produce more blooms as it is too late in the season then. (Done earlier in the season the plant has the ability to bloom down low).
That will help reduce the "seed bank" within the soil, which over the course of a few years can make a difference in how much Japanese Stiltgrass that you have.


Christine