It's Stiltgrass Time Again

As summer is peaking so is the time to focus on removing Japanese stiltgrass, Microstegium vimineum.  At this time (beginning of August) in the Mid-Atlantic region this invasive grass is putting on a growth spurt, but has not yet begun to develop viable flowers. In one of my previous blog posts on this subject I prepared this table to help keep track what to do to combat stiltgrass at each point in the season.

Season	Actions	Pros	Cons	Comments
Late Winter Early Spring	Pre-emergent treatment	Effective in lawns and smoother (even) surfaces with access to soil surface.  Allows lawns and perennials to get a head start.	Will affect all germinating seeds for several months.  Uneven coverage on rough surfaces.  Application needs to be at the right time.	Takes at least 2 years to knock down seed bank to see significant progress.  More time to complete elimination, if ever.
Late spring-Summer	Herbicide	Grass selective herbicide leaves broad leaf plants and some sedges intact. Try products containing Fluazifop-p-butyl	Difficult to control collateral damage, especially with non-selective herbicides	Targeted application and use of selective materials may limit side effects.
Late spring-Summer	Pulling	Non-toxic and selective.  Opens space for other species.	Labor intensive; left over stilt grass will expand to fill gaps.	If removal is not complete this will need to be repeated at the end of summer
Late summer/Early fall	Cutting/ pulling/ burning	All methods to reduce the amount of seed	Need to complete actions before seed begins to ripen.	Copious amounts of seed being produced, need to be thorough and avoid spreading any ripened seed.

While it is too late to count on herbicides cutting close to the ground level and pulling at very effective methods to employ at this time in order to prevent Japanese stiltgrass from reproducing.  Because this is an annual grass, keeping it from reseeding goes a long way to eliminating from your environment.  In wooded areas and existing beds where there are many desirable plants intermixed with the stiltgrass I opt for pulling as my preferred approach.  Since it has grown fairly tall by this time, I usually pull it by the handfuls then leave it out in the sun to dry.  If you are weed whacking it you could leave the cut grass in place to dry; however, I’ve read that doing this can generate a thick layer of thatch that can be difficult for other plants to grow through.  Whenever possible I will rake out the cut grass and leave it in the sun.  If I’m confident that there is no viable seed in the stiltgrass I will mow over the dried grass to help return that organic material to the soil.

For several years I have been removing stiltgrass manually from this
shady mossy lawn.  This year I treated it with a preemergent herbicide
 in late April and am seeing only a few instances of stiltgrass.  In addition
to the moss and some fine fescue and sedges there are patches of selfheal,
Virginia jumpseed and white avens. 

I’ve noticed that this year that the stiltgrass is more brittle and harder to pull cleanly out of the ground.  This may be due to the drier weather that I am experiencing at this time.  I’m afraid that I may be leaving more rooted fragments that may be able to regenerate.  I will try to time my next pulling campaign to be after a significant rainfall to soften the soil. 

Another thing I’ve noticed this year is that the plants that I am pulling up have multiple rooting points along the stem.  I’m thinking that as I am reducing the number of stiltgrass plants, year by year, there is more room for them to spread laterally.  So a partial success, but it means that there is still more work to be done.

I've treated this woodland path for two consecutive years with a
preemergent as indicated by the white line.  You can see the
bright green stiltgrass to the back and on the right. In the treated area
are a variety of grasses and sedges.  Deer tongue grass is the
largest species here.  In late March this area is covered with spring beauties.

Looking over my property I see that the most significant reduction in Japanese stiltgrass is where I have applied a preemergent herbicide in early spring.  This year I applied Dimension™ (dithiopyr) at the higher recommended rate.  This is expected to be effective for 3-4 months.  It was applied at the time recommended for crabgrass control (380 GDD(32°F)), or about the time when the forsythia were coming into full bloom.  I am seeing next to no stiltgrass in many parts of the lawn as well as in the treated parts of my ‘mown meadows’.  Better results are seen where I have treated for at least two consecutive years.  In these meadows and in the more natural areas I try to avoid treating the same area with a preemergent two years in a row.  This is to allow the seeds of the many desirable plants to germinate on the off-years. 

As far as native plants that compete well against Japanese stiltgrass, golden ragwort, Packera aurea, seems to actually suppress the growth of stiltgrass.  Virginia wild oats, Elymus virginicus, and bottlebrush grass, E. hystrix,  compete well.  What I believe to be fowl manna grass, Glyceria striata, has been able to out compete Japanese stiltgrass in shady moist areas.  This grass develops early in the year with tall, thick growth that shades the ground.  The downside of this grass is that it dies back to the ground after going to seed in late June.  

This photo, taken at the end of May, shows thick growth of
a grass that I believe to be fowl manna grass.  The area inside
the white circle has been free of stiltgrass for the past two years.

 I have been posting blogs about my battle with Japanese stiltgrass since 2014, probably 3-4 times a year.  Following are links to several of the more informative posts.  Getting Ready for Stiltgrass 2021, July 2020 What to do about Stiltgrass Now, The Forsythia are in bloom, Now is the Time, and Making a Plan to manage Japanese Stiltgrass.

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).

Fall Grasses

We've had a long and relatively mild fall here, that is until this week when overnight temps got to the low 20's.  Many trees held onto their leaves for a long time wait for a real cold snap to trigger leaf drop.  The Fothergilla I planted last season finally turned the fluorescent orange that I was hoping for.

As the temperature dropped the leaves of this
 Fothergilla 'Mt. Airy' changed to this intense orange color.

It got me thinking about my plant selection.  I am always looking out for plants with exciting fall foliage, reds, golds and oranges.  It got me to thinking that these are more effective when contrasted with cooler or muted colors like pale yellow, green or tan.

One class of plants to fill that role are the native grasses. Late or warm season grasses that produce flowers and seeds in the fall are particularly effective.  The low angle of the sun late in the year really plays off the seed stalks, bringing them to life.  I usually leave these stalks standing through the winter to get the most out of them.  I'll clean up what remains in the spring.

Another benefit of these grasses is as a food source for birds and as shelter for many insects and overwintering animals.



Here are some of the grasses I have that are showing off nicely this fall.

I have planted inland sea oats (Chasmanthium latifolium), aka, Northern sea oats and several other names, along a sloping area by the house subject to erosion.  This grass produces a dense fiberous root system that holds the soil well.  While its native habitat is in moist shady locations it will also tolerate dry shade.  It sprouts early in the spring and can spread, both by expanding clumps and seeds, to form dense stands.

The broad leaves of Inland Sea Oats has a bamboo-like appearance.
These copper colored seeds will persist into winter.

The plan is for this Pink Muhly to fill in along this fence.

When they open the flowers look like exploding fireworks.

Another grass that I have added to the property is Pink Muhly Grass (Muhlenbergia capillaris).  This species is native to the eastern US and the gulf coast, but you're not likely to find it naturally in the mountain regions where I am.  The reason I put this in was the light-catching effect of the flower plumes.  At first I was concerned that this effect would not be strong because I didn't have a good angle for the backlighting. But that's not a problem.  The photo above was taken at 2 PM and there is penty of light being scattered by the flowers even though the sun is still rather high in the sky.

I've found this plant to be slow to establish here. Some of that has to do with competition from the surronding plants. Clumps of pink muhly will expand, but it is not an aggressive spreader.  Larger masses should be mown or burned back in late winter to clean up the clump.

This clump of little bluestem is easily identified
by the silvery seed tufts along the stem..

These next three species are growing wild around my home.  Little Bluestem (Schizachyrium scoparium) is a common native species around here.  It is well suited to dry sunny sites.  It grows well in poor soils.  In excessively rich soils it puts on too much growth and flops over.  As a warm season grass it grows to 2-3 feet by mid-summer.  In the fall it turns golden and produces fuzzy white seeds along the upper stem.  These catch the light and envelop the stem in a silvery glow.  Some selections of little bluestem take on redder shades in the fall.   Small birds feed on the seeds, so I leave these up all winter.

One of the more distinctive grasses I have is Deer-tongue grass (Dichanthelim clandestinum, formerly Panicum clandestinum).  It has relatively broad leaves compared to other grasses.  It is a cool season grass, producing terminal spikelets in early to mid-summer.  Unlike most other cool season grasses, branching and growth continues through the summer.  The name, deer-tongue grass, refers to the shape of the inch-wide leaves, not to any preference for deer to eat it.

Deer-tongue grass persists well into fall, here as a deeply textured mass.

No longer colored, the seeds of Purpletop still catch the light.

Another common pasture grass here is purpletop (Tridens flavus).  When it first blooms in late summer it has a reddish purple color.  When distributed through a field, these blooms cast a purplish haze over the scene.  As the seeds mature the color is lost and the seed stalk becomes a brownish-gold.  As a pasture grass it is very palitable to livestock.  It is also a larval host to a variety of butterflies.

I have not seen purpletop used in any designed plantings, though it does have some interesting features.  The red colored flowers are best appreciated en masse and at a distance.  What might be useful in a smaller garden is to use the 3-4 foot tall flower stalks as a translucent screen between plantings.  Since the leaf blades are concentrated in the lower half of the plant they would not block a view across a planting.  Purpletop grows well on dryish soils in part to full sunlight.