Stiltgrass Fall 2019

I'm continuing my multipronged attack on Japanese stiltgrass, Microstegium vineum, that I have been waging for about 5 years now.  Depending on where the stiltgrass is growing different techniques are more effective.

Here are links to some earlier posts on my campaign against stiltgrass: Spring 2019, Spring 2018, Fall 2017, Original Plan 2014, and Use of Pre-emergents.

Woodlands  In the  shady woodland settings pulling the stiltgrass through the summer and especially in late summer just before blooming has been pretty effective.  In several of these shady areas removing the stiltgrass before is sets seed has shown good results after two seasons.  It is important to continue to follow up year after year to prevent a re-infestation.  When I first started do this I used a weed whacker to cut very close to the ground and I left the cut grass in place.  In places where I removed the cut grass progress toward eliminating it seemed to go faster.  Also as other, hopefully native, species begin to fill in, weed whacking risks cutting out those species as well.  Now I've gotten to the point of hand pulling the stiltgrass and piling it up in segregated locations where any seed present will be less likely to spread.

Here are some clumps of Virginia wild rye growing under a young tupelo tree. 
This is a cool season grass, seen here in June.  By the end of summer
 it will be golden brown with arching seed heads.

Bottlebrush grass is also a cool season grass that like partly sunny sites. 
These early season grasses have a chance to shade the ground before
the stiltgrass begins maturing in July

In these locations I have been trying to have more native species fill in, by either encouraging the existing natives of adding new ones.  Virginia wild rye, Elymus virginicus, is a native grass that grows pretty well in the shade, as is bottle brush grass, E. hystrix.  Other species that are filling in on their own are Virginia jumpseed, Persicaria virginiana, and clearweed, Pilea pumila.   A variety of smartweeds are also increasing, but I fear many of those are non-native species.

Clearweed is a native annual that has had a banner year here in 2019. 
It grows well in shady locations.  

Meadows  I've been having more trouble in the open meadow sites.  Some of this is my reluctance to do anything but hand pull.  I am trying not to disturb the more desirable species that co-inhabit the meadows.  In one area that I have been hand pulling for 3-4 years I'm seeing a reduction, but it still has a long way to go.  This past spring I put some pre-emergent  in several meadow areas and saw a further reduction in stiltgrass density, but not an elimination.  I also tried burning a patch of ground in early spring but that had no noticeable effect on the amount of stiltgrass.  (That is consistent with what the Forest Service reports on the use of fire.) 

By virtue of how stiltgrass grows, sending out shallowly rooted runners to fill all available space, by the end of summer you will have a similar density of flowering stalks whether you have 10 or 50 seedlings per square foot.  (These are my impressions, not proven facts).  But having fewer rooted individuals means it gets easier to clear an area by pulling because so many of the stems are interconnected.  I will try the pre-emergent again this spring, but do the application earlier (read on below).  One of my concerns in the meadow is that the pre-emergent will inhibit some native species from growing/reproducing.  I did not go in and inventory what was or was not growing in the treated and untreated areas.  I did see smartweeds and tick trefoils, Desmodium panniculata,  growing in all areas.  Where stiltgrass was growing thickly the ground plane was essentially barren after the grass was removed.

In May stiltgrass seedlings are less than an inch tall.  The right side of the area
was treated with Dimension pre-emergent herbicide in the first week of April. 
The untreated side has a greater density of stiltgrass seedlings.  I expect that
 applying the herbicide earlier in the spring will further reduce the amount
 of sprouted stiltgrass.

This is the same area, photograph from behind.  The treated side (left)
 has a slightly lower density of stilt grass, but still
 most of the available space is filled with stiltgrass stems.

Removing stiltgrass from the lawn.  Pre-emergent herbicide is still showing very good results.  2 years ago I applied herbicide (Dimension^tm) around the 3rd week of March.  While in the spring of 2019 I waited until the first week of April.  Or using the forsythia bloom as an indicator of spring weather, mid-bloom in 2018 and late bloom in 2019.  Despite the presence of the herbicide I did see more stiltgrass seedlings in 2019, so I think applying the pre-emergent earlier may be more effective.  For folks in the Northeast and Mid-West  there is a website that helps with the timing of pre-emergent application based on degree days.   Another problem with getting stiltgrass out of the lawn is that repeated mowing can stimulate earlier formation of flowers lower in the plant.  These are much harder to remove than the terminal flowers that form on undisturbed plants.

Here is some stiltgrass pulled from the lawn after mowing.  You can see
 how low in the plant the stem flowers (cleistogamous) occur. These flowers
 need to be cut off for mowing to be really effective at eliminating stiltgrass.

Some folks have reported success with cutting the lawn really low in August, the beginning of flowering season.   Looking at some of the stiltgrass growing in the lawn, it looks like you would need to cut down to about an inch to reach those lower flowers.  I tried that in one section of my lawn that I have not otherwise treated and is mostly stiltgrass.  Next spring we'll see how that area compares to normally mown areas. 

After you manage to suppress the stiltgrass you need to get something else growing in its place.  The easiest option in the lawn is to overseed with a well adapted turf grass.  In the Mid-Atlantic the commercially available options are tall fescue blends for sun and fine fescues for shade.  In my rural setting I also have many other grasses growing in and around the lawn.  Some of the native species that are mixed in include path rush (Juncus tenuis), purple top (Tridens flavens), nimblewill (Muhlenbergia schreberi) and a variety of sedges.  While I encourage these to grow, they would be much happier if they were not mown on a regular basis.  Nimblewill, though, does seem to tolerate mowing pretty well.  

This is what nimblewill looks like in the lawn.  This warm season grass is
 not as 'pretty' as commercial turf grasses, but is is native and is well adapted to
 the climate here, even in this unseasonable hot and dry year.

I was planning on overseeding a large area in early fall, but here in Maryland it has been unseasonably hot and dry so I have been holding off seeding until the weather cools.  Getting the new seed established in the fall is critical to using most pre-emergents because they will suppress growth of most weeds planted in the spring. 

Another option to turf grasses is to convert from lawn to meadow or other types of plants.  Based on my meadow experience you should get rid of the stiltgrass before just adding other plants.  This can be done chemically, by solarizing (covering with plastic for  enough time to kill the stiltgrass seeds), or covering with cardboard or many layers of paper followed by mulch or clean soil and then planting on top.

In one shady area of lawn I have using timed mowing as the primary means of stiltgrass control.  I leave the area unmown from mid-June until mid-August.  At that time I'll pull out and remove the tallest grass and follow up with a low mowing.  After 3 years of this I am getting less stiltgrass, but it is still pretty thick.  One explanation is that there is a lot of stiltgrass in the surrounding area and the seeds may be coming in from there, either blown in or carried by the rain.  I did put down some pre-emergent in a small section of this area and there was no stiltgrass present there.  Mosses and perennial grasses seemed unaffected. 

The vegetable garden  In the garden one of the places stiltgrass flourishes is along the fence line.  It interlaces with the chicken wire and can be hard to remove completely.  This year I have been using a flame weeder to clear those areas.  This method is more effective early in the season when plants are smaller and more tender.  As weeds mature they have more moisture in their stems and leaves and are more difficult to kill with heat.  One caution with using a garden torch is not to expose soaker hoses or drip irrigation lines to the direct flame.  Unlike some weeds a soaker hose will not recover after being melted. 

Next steps: 

• Overseed with turf grass.  For next season  I am going after a large open area that is mostly mown stiltgrass.  I will use pre-emergent on this area in early spring assuming I can get the new seed established.
• Continue use of pre-emergent in lawn areas where stiltgrass is depleted.  While I have not been targeting it, the amount of hair cress, Cardamine hirsuta, a winter annual weed, seems to be decreasing in the treated areas as well.
• Continue testing pre-emergent in meadow, this time apply earlier in spring
• Expand areas in the woods where stiltgrass has been pulled.  Try and remember that the best strategy for removing invasive species is to clear a small area really well and then expand that area each year.  Also start in a less infested area and then move to higher density areas.  

Stiltgrass actions for Spring 2019

I have been battling Japanese stiltgrass, Microstegium vimineum, for the past 5 years or so.   Pulling stiltgrass out, particularly in late summer, in the shaded woodlands has been effective in reducing the amount of stiltgrass over several years.  Getting it out of the lawn is another matter.  I've tried raking it out in late summer, and over planting with more desirable grasses (particularly fine and tall fescues).  This has helped, but stiltgrass as a warm season annual, is very adept at filling any gaps in the lawn starting in mid-spring.  While I really like the look of the fine fescues,  particularly the no or low-mow fescue blends, these are slow to establish.  The tall fescues are more aggressive than the fine fescues.  When over-seeded in late summer, these do a better job of getting established and filling in the gaps. 

The area outlined in black has been burned with a garden torch in late summer for the past two years. 
The control patch in the middle was not burned; it has slightly less coverage with perennial grasses.

More recently I've used a garden torch in late summer to eliminate it before it can set seed.  This has been somewhat effective but that is not so practical for a large area.  

Last year I used a pre-emergent herbicide, like those you would use for crabgrass, for the first time.  It was very effective at suppressing the stiltgrass for an entire season.  (I should say that the chemical's effect is probably gone after 2-3 months, but by that time the stiltgrass germination rate has dropped.)  Other perennial grasses were able to start filling in.  I will expand the area of application this year and also test it in some of the meadow areas, as well.

The treated areas have a little more coverage with perennial, mostly cool season, grasses than the untreated areas. 
The brownish spots are mostly zoysia or nimblewill, both warm season species.

While Japanese stiltgrass has a very high rate of germination, I expect that there may be some that waits a season of two to germinate, so these pre-emergent herbicide treatments may need to be repeated for several years.  I will try to leave a small area that I treated last year  untreated this year to see how strongly the stiltgrass comes back. 

In a blog post last year I mentioned several pre-emergents that were effective.  This year I will be using the same as last year, dithiopyr, sold as Dimension.  It has the advantage that I could find it alone, without added fertilizers.  Also, it was less expensive than Preen garden weed preventer (trifluralin).  Timing-wise, the general recommendation is to put the pre-emergent herbicide down when the forsythia are in bloom.  Last year I did this on the early side, just before peak bloom.  This year I will wait just a little later.  My thought is that this will give the existing grasses a little more time to spread before I put down the herbicide, which works by inhibiting new root growth near the soil surface.  I recently found a website that give guidance on when to apply pre-emergent herbicides and other turf related IPM activities called GDDTracker.  A nice feature is that it compares the current and previous year's temperature histories.

I will also try the pre-emergent herbicide in an area that I mow only once a year then leave to grow as a meadow.  In one section I burned off the surface debris.  Half of this I will treat with the pre-emergent, the other half will be untreated (Burn Only).  I will also treat an unburned area with the herbicide to see if burning makes a difference.  The rest of the meadow will serve as the 'control' group.  I am a little concerned about using the pre-emergent herbicide in' wilder' areas.  It could have a negative effect on some of the native annuals there like sweet everlasting, Pseudognaphalium obtussifolium, and yellow fumewort, Corydalis flavula.  But, then again, the stiltgrass has a definite negative effect.

Here is a section of my 'Mown Meadow' where I will do a Stiltgrass/Pre-emergent experiment.  This will give me an idea of how much prep work is needing in this wilder area.

Another action that I will be doing is to plant some bottlebrush grass seedlings, Elymus hystrix, into areas that are infected with Japanese stiltgrass (some herbicide treated, others not).  Bottlebrush grass does particularly well in open shade, conditions that Japanese stiltgrass excels in.  Just removing the stiltgrass alone is not enough, I need to establish some desirable native species to keep the stiltgrass out.

The Forsythia are in bloom, now it's time to...

The blooming of Forsythia is a signal to begin a number of outdoor tasks.  It signals a good time to apply preemergent herbicides for control of summer annual weeds.  I'm giving this a go this year as another tool to get rid of Japanese stiltgrass, Mircostegium vimineum, from my property.  I've been making progress in the woods where I have been pulling it out in July and August as it is getting tall.  Getting it out of the lawn is another matter.  

It's the end of March, and although the Forsythia started blooming
at first in January, I think they are doing it for real now.

There, repeated mowings keep it short and actually induce early seed formation in the lower stems.  I have been raking/combing it out of the lawn in a few areas but that does not seem very effective.  It seems that while I remove a lot of the weed, any remaining stiltgrass just expands to fill in the gaps.  So while I prefer to avoid the used of synthetics, I've tried going it alone for a couple of years and now I need some help.  

Many of the common preemergent herbicides used for crab grass control have been found to be effective on stiltgrass when applied prior to seed germination.  Preemergents that have been shown to be effective include Dithiopyr ('Dimension'), Pendamethalin ('Pendulum'), Prodiamine ('Halts') and Trifluralin ('Preen Weed Preventer').  One of the challenges is finding a preemergent that does not come with added fertilizer.  In my case I do fertilization in the fall, since I am growing mostly cool season grasses, particularly fine fescues, Festuca rubra cultivars.  Fine fescues have low fertilizer demand and I see no good reason to apply fertilizer at a time when weeds are about to take off. The product I found contained only Dithopyr, no excess fertilizer.

Hairy Cress is a winter annual weed that has been taking over here.  Last year I mowed
it early before much of it started producing seed.  This year I'm hoping
 to get some added help from the preemergent herbicide.

As an added bonus this may help control the hairy bittercress, Cardamine hirsuta, that is growing in the lawn.  This weed is a winter annual, sprouting in fall and again in early spring.  While it dies back by mid-spring, this creates gaps in the turf that provides space for the stiltgrass to fill in. 

Dithopyr works by interfering with development of new roots, after seeds have germinated.  Perhaps I should have waited a little longer to put this down in order to allow the existing grasses to get further along, but I didn't want to forget. We'll see how all this works out later in the summer when I can compare treated and non-treat areas for amount of stiltgrass.  Check out this earlier post for some things I tried last fall. 

Last Comments on Stiltgrass -- This Year

I've been talking a lot about Japanese stiltgrass control and how I am trying to eliminate it from my property.  One of the really insidious features of stiltgrass is that in addition to its normal seeds produced on tall stalks, it also produces a second set of seeds on flowers enclosed in stems close to the ground.  These are referred to as cleistogamous flowers.

Here in mid-October you can see the height difference
between the regular flowers and cleistogamous ones.

While removal of the upper flowering parts of the plant will help control the spread of stiltgrass and reduce the total number of seeds produced, that second set of seeds keeps the local population going.  These cleistogamous flowers are particularly relevant in mown lawns, where these ground-hugging flowers survive the regular trimming.

An approach that I am expanding on further this year is to use a stiff rake to pull out the stilt grass from the lawn.  This works best when the desired grass is clump forming.  The rake can get locked into the creeping stolons of the stiltgrass, while the clumping grasses are not snagged (too much).  Timing is critical -- wait until late in the season when the expanding lateral growth of the stiltgrass makes it easier to snag, but before the cleistogamous seeds begin to mature.  This year I did a thorough raking at the end of September.  That worked out with the timing for overseeding the lawn with a more desirable grass seed.  When I went out a week later I noticed that some of the stiltgrass in the lawn did have seeds forming in the lower stems.  Next year I will do the raking in early or mid-September to reduce the chance of actually spreading any matured stiltgrass seed while raking.

Here are the piles of stiltgrass and other debris I raked out in preparation for overseeding
the last week of September.  The 4 smaller piles are from an area I overseeded
with tall fescue last year; the larger piles are from a new area I started this year.
After drying for a couple of days these piles were carefully carried away to a segregated brush pile
to avoid spreading stiltgrass seeds.

A general strategy for removing invasive plants is to start with a manageable sized area and clean it up thoroughly.  In subsequent seasons expand the area for cleaning.  This reduces the chance that the previously cleaned areas become reinfested.  Trying to do too much at once risks leaving many seeds or plants behind that will reinfect your 'clean' areas and real progress will difficult.

Collecting my own seed

I've been trying to figure out what to plant in the areas where I've been pulling out the Japanese stiltgrass.  I want to use native plants and I'd like them to be as local as possible.  As I was taking some autumn photos, suddenly it hit me.  Why not use the seeds that my native plants are producing right in my own backyard (duh)!!!  This is perfect.  By collecting seed from around my property I'm getting plants that are adapted to the local area.  I can also make a good guess at where the plants will grow well.  Of course not every seed I put out will germinate but the seeds are free and the investment in labor is minimal.  The seed I am collecting now are from late summer and fall blooming plants.

Here's what I've collected so far:

The ripe seed heads of this Sallow Sedge fell apart into individual
seeds when I touched them making them easy to harvest.

Sallow sedge, Carex lurida, is pretty common on my property.  It forms dense clumps that mature to 2-3' tall and wide.  It grows best in moist to wet soils and partial sunlight.  I have small clumps of it growing in the lawn, but these can't reproduce since they are getting mowed down regularly. The leaves are long and have a deep fold along the midrib.  This gives it a stiff texture.

I'll scatter the seeds along the woodland edges where the soil is moist and there are several hours of good sun each day.  It is also an area where I am trying to remove the invasive wineberry bushes, Rubus phoenicolasius.  The dense clumps may make it a little harder for these bushes to spread.

The seeds of bottlebrush grass are easily stripped off from
bottom to top.  Trying to go the other direction leaves most
of the seed still attached to the stem.

Bottlebrush grass, Elymus hystrix, is a common cool season grass of the northeastern quarter of the US.  Most of the plants I have were purchased, however I have seen some growing remotely.  So I may have some indigenous plants, or they are just really good at spreading.  This species is most noted for the flowers and seed heads that resemble a bottle brush.  The flowers appear in early summer and persist until fall.  

The plants grow from 2 to 5 feet tall and do well partial sun and soils with medium moisture levels.  I will plant these along the edge of a path where the soil drops away.  The height of these plants should still make them easy to see.

The seeds are relatively large.  One ounce typically consists of about 7,500 seeds

Ripe seeds are assisted in wind dispersal by the fluffy white appendages.
Some flowers still in bloom are at the lower right in the photo.

Tall Snakeroot, Ageratina altissima, formerly Eupatorium rugosum, is very common in this area.  It is particularly evident in my area along roadsides near the Potomac river.  It grows well in full to partial sunlight and a range of soil moistures.

It is tolerant of soil disturbance, making it a good candidate for an edge habitat where plants are occasionally mowed down.  I'll scatter these in some of the drier woodland edge areas.

The seeds are tiny, typically 150,000 per ounce. They require light for germination.  This is common for disturbance adapted plant species.

Here most of the fluffy seed of the Sweet Everlasting have 
been blown away, leaving the sepals as 'everlasting' flowers.

Sweet everlasting, Pseudognaphalium obtusifolium, is a native annual that depends on disturbance for survival.  It is most common recently cleared areas in full sun and dryish soils.  I have a recently cleared meadow area that will be perfect for these.

This plant is evident in a border because the fine hairs on the leaves and stems catch the sunlight and make it look like the plant is glowing.  The tiny white flowers never fully open but form white clusters of buds that show well.  After blooming long-lasting bracts remain giving the effect of an everlasting flower.

The seeds of this species are really tiny, coming in at 500,000 per ounce.  It is hard to find the actual seed, there is so much fluff attached. These seeds are quickly wind dispersed, so I need stay on top of harvesting them.

Short's Aster, Symphyotrichum shortii, is found in the mid-Atlantic and mid-western states.  This aster is the latest blooming species that I have growing.  It starts in about mid-September and continues to the end of October.  Besides its long and late blooming cycle, it is also tolerant of dry shade and alkaline soils.  This makes it an excellent candidate for deeper into the woodland areas where it can compete with the stiltgrass for patches of light and openings in the canopy.

Each seed of Small's Aster has an attached pappus that looks like a little umbrella that catches the wind.  The actual seeds are larger than the previous two species, with about 60,000 per ounce.

In the center are some ripe seeds with their fluffy pappus.
In the background you can see some or the lavender
flowers still in bloom.

So these are some of the later blooming species that I will try to 'seed' into the stiltgrass infected areas.  There no reason I shouldn't harvest some of my spring and early summer species and do the same.

Stiltgrass management, part 2

After trying to remove as much Japanese stiltgrass as possible in late summer, the next step is to fill in the gaps with more desirable plants. My approach last year of seeding in native grasses like Canada and Virginia ryes did not work out too well.  There were some good reasons for my disappointing results.  I needed to plant  these relatively large seeds more deeply to get better germination.  Also these new grass seedlings need 2-3 years to establish before mowing back, or using as pasture.  It would be better to use these big perennial grasses in a meadow planting where mowing is done only once a season.

This year I am trying a more conventional route with the filler grasses.  I will be using commercial turf grasses that are selected for rapid growth and formation of a dense turf layer.  This is what I need to exclude the stiltgrass.  By planting these cool season grasses in the fall they have a chance to germinate and fill in before the stiltgrass starts growing in mid-spring.

I divided up the stiltgrass infected areas into full sun, part sun and mostly shade and selected a seed mixture appropriate for each condition.  For full sun I selected a blend of tall fescues with just a little Kentucky bluegrass.  For the part-sun areas I have a blend or both tall and fine fescues with a little perennial rye and Kentucky blue grass.  For the shade areas I am using a blend of fine fescues selected for low maintenance.  This year I am using Eco-Grass from Prairie Moon, but there are other blends such as No-Mow from Prairie Nursery and Eco-lawn from Wildflower Farm that should work as well.

Most commercially available cool-season turf grasses are not native to North America with the exception of some of the fine fescues, in particular red fescue (Festuca rubra).  You can find detailed information about which turf grasses are appropriate for your region from your state's cooperative extension.  For example the Maryland Extension Service has a listing of recommended grass cultivars that were tested locally.

Before buying seed this year I shopped around to see what specific seed cultivars were used in each of the blends.  There is usually a tag with the detailed seed composition somewhere on the bag. When I went out to buy the one I liked, I found that that specific blend was no longer available even though the product name on the bag was the same.  Frustrating!!!  I imagine that the retailers are still trying the produce an equivalent performing product, but it still, that was a frustrating experience.

The first step in the reseeding process is to remove the stiltgrass thatch in the lawn.  This opens up spaces for the new seed and may help remove some undispersed sitltgrass seed.  Since late in the season much of the remaining stiltgrass has had a chance to set seed, this thatch needs to be segregated from regular compost and the regular brush piles.  I have a couple of piles dedicated to stiltgrass so that it does not get mixed up with the regular yard waste and I can monitor it for spreading.  Another option would be to landfill it in thick plastic bags.  You do not want to let the stiltgrass get out and spread its seed.

Late September is when the stiltgrass begins to die back.  The brownish areas are easy to spot.

Once the area was clear of thatch I applied the new seed.  I used the back side of a bow rake to press the seed into the soil.  The nice thing about the conventional turf seeds is that they do not need to be planted deeply.  After sowing, it is necessary to keep the new seed bed moist until the new seedlings are established. I usually try to time my seed sowing with coming rains.  That way I don't need to water it in (I'm really lazy in that way).  Besides the cooler temperatures, autumn is a good time for lawn seeding because it is usually a rainier then too.   I usually see good levels of germination in 10-14 days for the Eco-grass.  This year is working out well (so far).  The soaking rains in early October saturated the soil and I have only needed to add a little additional water to keep the soil moist.

The area between the piles has been (mostly) cleared of stilt grass and is ready for seeding.
I used a leaf rake for this, but a stiff garden rake would have been
more effective for tearing out the stiltgrass plants.

While the standard instructions on the seed bag recommends fertilization at the time of seeding, it is best to do a soil test to determine if added fertilizer is needed.  If you use a mulching mower to return your grass clippings and leaves to the soil your fertilizer needs will be much lower (or non-existent). The risk of over-using fertilizer is that it will stimulate weed growth and that run off of excess nutrients will damage the environment.  Since we are in the Chesapeake watershed I try to use the minimum of fertilizer possible.  That usually means none.  In fact, for the fine fescues fertilization is not recommended.  If fertilization is needed, fall is the best time for cool season grasses.  Spring fertilization will stimulate growth of warm season weeds (and stiltgrass) as well as the cool season grasses.  In the fall only the cool season plants are actively taking up nutrients.

In this full sun area tearing out the stiltgrass exposed a lot of bare ground.
This spot was seeded with the full sun blend.  Just to the back left
 is a full shade area where I planted the Eco-grass mix.

One new thing I learned about tall fescue, Lolium arundinaceum, is that some cultivars are infected with an endophytic fungus that produces loline alkaloids that are toxic to many insects and mammals that feed on the grass.  This endophytic fungus also reduces biodiversity around the infected fescue.  while this is great for the fescue it is bad for the wider plant and animal communities.  The widely used and inexpensive cultivar K-31 has a high rate of infection.  So far I have not been able to find out which cultivar have low infection rates, however this may be more common in southern states.  One way to lower the effects of infected fescue on the environment is to keep it mowed so that it stays in a vegetative state, i.e., not going to seed.  Hopefully its ability to form a good turf and exclude the stiltgrass will outweigh it negative environmental effects.
..

Stiltgrass is in bloom - The time to act is now!

The flower heads of Japanese stiltgrass are just opening up.
The weedy plants have just had a growth spurt
bringing some of them to nearly 4' tall.

I am in midst of a multi-year battle to get rid of, or at least control, the Japanese stiltgrass, Microstegium vimineum, on our property.  Last year I came up with a plan to bring this invasive species under control.  The key element is to prevent this annual grass from setting seed.  Eventually (5-7 years) the seed bank will be depleted.  Also I am encouraging the existing native plant population to back fill the gaps to suppress re-invasion.

In late August stiltgrass goes into a growth spurt as the flower heads develop.  It is critical to cut it down or pull it out before seed set begins.  By killing the plant before the seeds can mature, you can dispose of the plants by composting.  Otherwise the plants would need to be segregated (e.g. bagged and sent to landfill) to prevent another generation of seed from spreading.  The taller stiltgrass is easier to find and pull than it is earlier in the season.  You should try to remove the plant close to the ground since it also produces a second hidden (cleistogamous) flower in the lower stem.


The following two photos show a moist shady area just before I removed the stiltgrass.

One year after close cutting stiltgrass in late August (2103) the growth is still rather dense.

After two years of cutting there appears to be more gaps in the stiltgrass converage.

In a couple of areas I was weed whacking and composting in place.  After 2 years of this I am seeing some minor decreases in the density of the stiltgrass coverage.  This year I raked the cut grass off and into a pile.  By removing the dense thatch I am hoping to seed some other species move in.  I have another large area where I will leave the cut grass in place.  We'll see if that makes a difference.

American germander blooms in late July and the seed is still maturing,
so I'd like to keep these standing a little longer.

One of my challenges is to remove the stiltgrass while leaving as much native vegetation in place.  Many of the earlier blooming natives, such as the beebalms (Monarda sp.) and tick trefoils (Desmodium sp.) have already gone to seed.  However, there are a number of later blooming species that I'm trying to preserve by carefully hand-pulling around them.  These include American germander, (Teucrium canadense), Virginia knotweed (Persicaria virginiana), white vervain (Verbena urticifolia), white avens (Geum canadense), and the native annual, clearweed (Pilea pumila).  While not beautiful plants on their own these species do fill the woodland edge with a variety of colors and textures largely obscured by the invasive stilt grass.

Clearweed is a fairly common native annual found in shady moist sites.
Currently in bloom, the flowers are yellow tassels in the leaf axils.

Here I'm halfway done with a section revealing some American germander (center).  To the left is my new grass whip.

I recently got a double edged grass whip which does a great job of ripping stiltgrass out of the ground while leaving single bladed grasses largely intact.

This low-growing sedge was hardly disturbed as the weed whip tore out the stiltgrass.

I am also finding a number of native grass species under and within the stiltgrass.  These include the evergreen, spreading sedge (Carex laciculmis) and deer-tongue grass (Dichanthelium clandestinum).