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.

I Planted ...What???

For a long time I’ve wondered why the great interest in exotic barberries and no mention of our native species, American barberry, Berberis canadensis.  From the design standpoint, Japanese barberry offers a wide variety of foliage colors and forms while, as it stands today, there is only the native form of B. canadensis available.  Of course the Japanese barberry, B. thunbergii, we see today is the result of much work in the horticultural field to develop all those unique forms.  This widespread use of Japanese barberry in the landscape has led to its spread into the wild.  Birds do like the red berries and deposit them throughout the landscape through their droppings.  Once established in the wild it is able to out-compete native vegetation as it is rarely browsed by deer.  Instead the deer turn to native vegetation, in many cases severely decimating the native plant populations.  Japanese barberry has also been associated with the spread of Lyme disease due to its tendency to harbor ticks.

This American barberry was planted in early spring
and has more than doubled in size since then.

 

Identifying features of American barberry are the
 three-pronged thorns and the teeth or bristles
on the leaf margins as indicted by the arrows.

American barberry, B. canadensis, is a mounding shrub growing from 2 to 6’ tall that can spread via underground stems.  It has 1-2 inch long spatulate leaves with widely toothed margins.  Its thorns are three pronged, which differentiates it from the single pronged Japanese barberry.  In the spring it bears drooping clusters of yellow flowers.  The flowers give way to red, edible fruits in late summer to early fall.  One concern with American barberry is that it is an alternate host for black stem fungus (rust) in wheat.  (European barberry, B. vulgaris, is the major offender which led to its near total eradication in wheat farming areas.  Japanese barberry does not act as a host for this disease.)  However this is not as significant of a problem within its native range south from PA to GA.  Native habitats include savannah and open woodlands, but these areas are decreasing due, in part, to fire suppression leading to increases in shade.  Some gardening sources indicate that American barberry will grow under a variety of conditions, in the wild it favors shallow, neutral to basic soils.

The reason I wanted to try now American barberry is as a replacement for Asian spireas.  In particular I’m looking for a mounding shrub that blooms in the summer and grows 3-4’ tall.  I would also expect that this barberry would be resistant to browsing by deer, but that is not confirmed.  I'm also looking at NJ Tea, Ceonanthus americana, as possible spirea substitutes.  More on that later.

I found this Eastern Wahoo growing in Beaver Brook Reservation
 in Belmont, MA.  The inset shows the deeply furrowed bark which
 appeared to take on a diamond-like pattern.

 The other new plant that I got this spring is Eastern Wahoo, Euonymus atropurpureus. It is a small tree or large shrub native to the eastern U.S.  I have generally been in the business of ripping out Euonymus species whenever I saw them.  This has applied particularly to burning bush, E. alatus, and wintercreeper, E. fortunii, both invasive species.  A number of years ago I came across an Eastern wahoo growing in an unmanaged suburban woodland in the Boston area.  The bright colored seed pods in fall and the diamond patterned bark were two attributes that sparked my interest.  What I found may have been a garden escapee since it is not native to the New England states. Its native range is primarily in the Mid-West; however, it does extend into parts of Maryland, as well as Pennsylvania, Virginia and West Virginia.  So when I saw that it was available at a regional native plant nursery I decided to give them a go.  It is quite shade tolerant so I put them in an area where I have been removing established tree of heaven, Ailanthus altissima, as well as seedlings of burning bush.

This photo, taken in early November, shows that Wahoo holds onto its leaves
fairly late into the year.  Most of the red arils have fallen from the flowers. 

One of the tricky aspects of planting eastern wahoo, while actively removing winged euonymus seedlings is that I will need to tell them apart, lest I remove a desirable plant.  The obvious thing is to make sure that I keep a recognizable tag on the wahoo and remember where they are planted.  Comparing young wahoo to burning bush seedlings show both to have some corkiness, but the Wahoo has it in straight lines and it is not as pronounced as on burning bush.  Also, the leaves of burning bush are stiffer and more narrow and pointed than those on a young wahoo. 

Here's a comparison of an existing burning bush (left) with
 an Eastern Wahoo seedling (right).