Monday, August 15, 2022

Pull! Pull! Pull!

 Yes Pull!  Now is the time to pull out Japanese stiltgrass, Microstegium vimineum.  This invasive species is rampant in the eastern U.S. from Georgia to Massachusetts and west to the Mississippi River.  It affects home landscapes and natural area alike.  Here in the Mid-Atlantic region the grass is putting on a growth spurt prior to going into bloom.  So the plant is expending a lot energy now to grow taller and produce flowers.  It also means that it is a lot easier to pull out without getting on you knees.  Since this grass in an annual, keeping it from going to seed can go along way to controlling its spread and reducing its numbers.  

Early in the growing season Japanese stiltgrass stays relatively low, rooting at several nodes along the stem.  In late July it starts growing upward to gets its flowers higher off the ground.  If it were only that simple.  Stiltgrass not only produces flowers at the top of the stem it also has flowers at most of the vertical leaf nodes buried within the stems.  These are referred to as cleistogamous flowers.  

  This image shows flowers at the top and at the
lowest nodes. Cleistogamous flowers can occur all
along the stem as well.  Roots can also form roots at each
node where they contact the ground. If the grass is not
cut early in the season most of the flowers are
concentrated toward the top of the stem.

These cleistogamous flowers are one of the reasons stiltgrass is so hard to eliminate.  If you cut or mow stiltgrass early in the season without removing it completely, these stem flowers will form even lower on the plant requiring even more careful pulling later on.  I've seen a recommendation to leave the stiltgrass grow until late summer so that most of the flowers are higher in the plant.  Then when you pull you are able to get most all of the flowers with the least effort.  (Sounds good to me.)

Here are some highlights of my nearly 10-year battle with stiltgrass here in Maryland:

Pre-emergent herbicides are very effective in existing lawns and smooth surfaces.  These chemicals interfere with the development of germinating seeds but do not have a strong effect on established plants.  These must be applied in early spring prior to the germination of the stiltgrass seeds.   I have been using a preemergent containing Dimension (dithiopyr) for several years.  I took two years of successive treatments to get nearly complete removal of stiltgrass from the lawn in treated areas.  Moss has not been effected. 

Late summer pulling of previously uncut stiltgrass, especially in shady areas, has reduced the amount of stiltgrass in subsequent years.  This does require a multiyear effort.  Since nasty things like poison ivy, multiflora rose and wineberry can hide in the tall stiltgrass, it is important to wear gloves and arm protection when pulling.

Here's the before photo.  I wonder why there is so much
stiltgrass just in this area, and why so close to the path. 
It could be from the lawn mower blowing seed from
 the other side of the path where there is a lot more stiltgrass

After about 30 minutes of labor you can see the
existing plants reappear. (Some of the freshly
pulled stiltgrass is piled in the foreground-left.)

Weed-whacking and raking of the cut grass before it begins to bloom is very effective, BUT you need to get really close to the ground to remove all the stiltgrass. Raking up the cut grass helps existing plants bounce back. 

Identify and plant native species that can compete with stiltgrass. Two exceptional plants that seem to outcompete stiltgrass are golden ragwort (Packera aurea), and mayapple (Podophyllum peltatum).  Other plants that are strong competitors include clearweed ( Pilea pumila) and grasses that grow well in shade: river oats (Chasmantheum latifolium), mannagrass (Glycera sp.), Virginia wildrye (Elymus virginicus), and  nimblewill (Muhlenbergia schreberi).  Also there are a number of sedges that will persist under cover of stiltgrass and can form a dense cover if given the chance.  Rosy sedge (Carex rosea) is one example that does quite well on my property.  I recently noticed that there was much less stiltgrass growing in an area where celandine poppy (Stylophorum diphyllum) and mannagrass have been spreading.  The exclusion of stiltgrass is not as great as with Packera, but it is noticeable.

This opening under the trees is free of both garlic mustard and stiltgrass now. 
In early spring it is fully covered with mayapples and a few woodland phlox.

The area just beyond the bench has benefited from annual late
summer pulling and by a dense crop of mannagrass that totally
shaded the area from late April to early June.  The stiltgrass that is
growing there now is only a few inches tall.  Compare that
to the 2 foot tall stiltgrass in the foreground-left.

It's not just pulling in late summer and fall.  There are things you can do earlier in the year to control stiltgrass.  Here is a table summarizing some removal strategies:

Japanese Stiltgrass Control






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 (same time as for crabgrass).

Takes at least 2 years to knock down seed bank to see significant progress.  More time to complete elimination, if ever. Many pre-emergents for crabgrass control are also approved for Japanese stiltgrass (aka Mary's grass, on the label)

Late spring-Summer


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


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.

You can read more information about my on-going battle with Japanese stiltgrass in previous blog-posts by entering 'Microstegium' in the 'Search this Blog' box at the top of this page.

Good luck and I would like to hear about your experiences battling this invasive species.