How to Kill Japanese Stilt Grass [SOLVED]

A Plan for Japanese Stilt Grass

Last year we put in a new lawn and to keep the costs reasonable we used seed instead of sod. We did this knowing that in the spring the weeds would return and we would need a method to deal with them.  So, we hired a very prominent and expensive grounds maintenance company to solve the problem.  We selected this vendor because we believed they had expertise where other firms did not.  In the end it turns out you don't always get what you pay for as they have only one maintenance program, regardless of the local conditions in your lawn.  Sadly their program did nothing for the Japanese srtilt grass.  In the end, our new beautiful lawn was again taken over by this invasive weed in the late spring and summer months leaving the problem to me (the computer guy) to solve.

Japanese Stilt Grass, What is it? 

According to the National Park Service, "Japanese Stiltgrass [Microstegium Vimineum] was introduced into the United States in Tennessee around 1919 and likely escaped as a result of its use as a packing material for porcelain."  It's an annual weed that grows from seed.  It is also less commonly referred to as "packing grass" and "Nepalese Browntop".  In my region (Northern Virginia) this invader is a very common sight along roadways and gravel paths and it seems it can grow in any light or soil condition.  It fact, is not uncommon to see it growing in complete shade.  The plant has interesting joints that resemble miniature bamboo.  The roots are flimsy and it's easily to remove by hand or cut down to the ground with a string trimmer.

The Department of Horticulture at the university of Pennsylvania has prepared a very informative but technical two-page Invasive Plant Species Management pamphlet on Japanese Stilt Grass that is worth downloading and printing.  The trouble though is that most people are not pursuing horticulture degrees, do not have access to the exotic chemicals, do not have spray or commercial applicators, and just want to know what can be done quickly and cheaply to solve the problem.  While there is no quick "one-shot" solution, below is how I killed it.

How to Kill It

If you have Japanese Stilt Grass living in and through your lawn, other than replacing your entire lawn with sod, there are effectively only two options: either pulling the weeds or killing them with a post-emergent herbicide.  "Post Emergent" is a fancy way of saying "actively growing weeds that have already come up from soil".  So, if you can see it, you need a post-emergent weed killer.

Do not think for a second that you are going to go to Home Depot and buy a bag of "weed and feed" to treat this problem--it won't have any effect other than to fertilize the stilt grass.

Before I did the research I tried "weed and feed" and some liquid weed killers--some of the other weeds in the lawn were affected but none of these methods did anything other than help the Stilt Grass grow.  The one exception was RoundUp (Glyphosate) which was effective at killing the stilt grass, but it also killed everything else including the good grass.

Finally I found Bayer Advanced 704100 Bermudagrass Control for Lawns on Amazon.

After reading some of the product reviews I gave it a try.  It was super easy to use--you just attach it to the end of your garden hose and then just spray the Stilt Grass.  One bottle treats about 5,000 square feet so it goes a long way.  The active ingredient is "fenoxaprop-p-ethyl".  I am quite sure any product with this ingredient will do the job, but the hose end sprayer meant makes it idiot proof.

After the application it did not appear to be working and I was ready to give up and try something else, but after about 10 days passed (including a few days of rain) I could see a noticeable difference in the stilt grass (it began to yellow and some of the other weeds in the lawn reddened).  See the image below.  This is what it looked like about two weeks later--note that the regular grass (what little was left) remained unaffected.  I have since learned that the product works as the weeds are growing and that explains why it takes some time to fully kill them.

(about two weeks after application of the Bayer product)

Here is the lawn at three weeks after application of the Bayer product.  A huge improvement, the invader completely dead (but not yet defeated).

(about three weeks--21 days--after the application of the Bayer product)

After about a month the areas that I had treated with a single application were entirely dead.  There was no noticeable affect to the regular grass which is what the product advertised.  The product says you can immediately re-seed with tall fescue which I should have done and didn't.  If you are going to re-seed with Kentucky Blue Grass, you are supposed to wait three weeks which would be the above picture.  None the less I was very happy to find this product and it made a very big difference.  I still have more work to do however, read on.

How to Eradicate It

Just because you have killed the Stilt Grass in your lawn doesn't mean that it won't come right back next year.  Japanese Stiltgrass can have a very extensive seed bank in the soil.  And according to the University of Pensylvania, it might take up to 5 years to completely rid your lawn of it depending on how bad it was to start.  This is where you need a maintenance schedule--the most critically component of which is a pre-emergent herbicide that prevents the grass from getting started.  PennState recommends applying an herbicide such as "Pendulum Aquacap" (active ingredient pendimethalin) at 4.2 qts per acre in the month of March.  I was able to find some of this herbicide on the internet through a Google search.

If you have read this far it means, like me, you want to declare war on the invader.  If so, best of luck to you and please share your own war stories in the comments below.