Getting Ready for Stiltgrass 2021

My battle against Japanese stiltgrass, Microstegium vimineum, is a nearly year round effort.  To help me focus my efforts I’ve prepared the following table to remind me of where I will get the most for each hour of work in each season.

Japanese Stiltgrass Control

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.

 Because Japanese stiltgrass is an annual there are two points of vulnerability based on its life cycle.  As an annual all plants start new from seed each spring.  If you can disrupt germination you can make a significant dent in how much stiltgrass you will have to deal with.  This is where I have found preemergent herbicides to be very useful.  Products labeled for control of crabgrass have proven effective.  The other weak spot is seed production in early fall.  More on that below.

On the left you can see the effect of a single treatment with
a preemergent crabgrass herbicide.  The right side is thick with
bright green Japanese stiltgrass.  Photo taken in early July.

Springtime

An important part of using a preemergent is getting it applied at the proper time, neither too early or too late in the spring.  There are tools on the internet that track growing degree days, such as GDD Tracker 4.0.  The idea is that plants will develop at a rate controlled by how much heat they receive over time.  For germination, the soil temperature is particularly important.  It is important to realize with a preemergent it is critical to have the material well distributed on the soil prior to the onset of germination.  That’s why I like a really like the calculator, it builds in the time when you should actually apply the product.  Another way to time the application is to watch for when forsythia are in bloom.  In my limited experience just before peak bloom is a good time to do the preemergent application.

I have found that preemergent use on the lawn is very effective.  There was a significant reduction in stiltgrass in the lawn after treatment for two consecutive years.  Also the red fescue that I overseeded is really starting to knit together.  I should do a test this year to see if I can skip treating a portion of the lawn for a year without a resurgence of stiltgrass?  Maybe for a small area.  I'd hate to lose the progress I've made so far.

I have also experimented with preemergent treatments in a meadow area.  Here the ground is much coarser and there is a lot of debris on the ground.  It is very difficult to get an even application of the granular herbicide.  I have seen a decrease in the amount of stiltgrass seedlings in areas where the preemergent was applied.  But there are also patches where the stiltgrass still comes in densely.  I assume that these are due to uneven application.    

Another concern I have with this meadow area is that the preemergent treatments will inhibit the germination of other desirable plants.  The meadow area I have is dominated by wingstem (Verbesina alternifolia), wild blackberry, smartweed and a variety of sedges.  In addition there are the usual invasives: Wineberry (Rubus phoenicolasius), Oriental bittersweet, Japanese honeysuckle and multiflora rose.  Besides reducing the amount of Japanese stiltgrass I have also noticed a significant reduction in the amount of bull thistle, Cirsium vulgare, a non-native species.  (Of course having a thick layer of JSG will also inhibit or kill anything that is not well established, so one needs to balance the effects of the herbicide with not doing anything.)  Last spring I transplanted in a number of black- and brown-eyed Susans (Rudbeckia hirta and R. triloba) and some wild bergamot (Monarda fistulosa) in the gaps that opened up.  It is particularly important for the ‘Susans’ that they be allowed to reseed.  For this year (2021) I will not do the preemergent treatment in the areas with these reseeding perennials.  Instead I will focus on some areas that have not been treated before.

Last year I did experiment with surface burning of stiltgrass seedlings.  While it did provide some temporary control, more seedlings appeared a week or two later.  For me burning with a torch is a maintenance activity and it’s easier than bending over to pick out seedlings.  Spring fire does not work as a one-time treatment in my hands.

Mid-Season

I have been reading more about grass specific herbicides and how they would fit into a plan for eliminating Japanese stiltgrass.  I can see using them as a tool in maintaining a perennial bed or in a well defined, designed landscape.  For me I don’t expect to be using them because most of my landscape is more like managed wildlands.  I generally welcome any native species that pops up annual, perennial, shrub or grass.  So I don't want to run the risk of killing something new and unexpected.

This patch of unmown grass has benefited from both regular pulling
of stiltgrass and a single treatment with a preemergent. 
As I've opened spaces I've planted in natives such as switch grass
and wild bergamot (taller plants to the back right).  The yellow flowers
are wingstem and goldenrods that have come in naturally.

Most of my mid-season activity is focused on pulling and back-filling with desirable, native species.  This year I will be moving many of my excess plants from the vegetable garden, Rudbeckias and Monarda, as well as some overgrown New England asters and goldenrods into spots where I will have weeded out the stiltgrass.  Native species that are competing well against stiltgrass include golden ragwort, mayapple, wild bergamot and grasses and sedges such as river oats, deertongue grass, Virginia wild oats, and rosey and sallow sedges (Carex rosea and C. lurida).

 

This patch of golden ragwort, seen here in mid-April, started from a
single clump planted 2 years earlier.  This species is very effective
at excluding both Japanese stiltgrass and garlic mustard.

6 years ago I seeded in Virginia wild rye.  It is particularly evident
in unmown, shady areas around trees.  This cool season grass gets
started early in the season, well before stiltgrass, and grows 2-4 feet tall.

If pulling is not complete, the remaining stiltgrass will refill newly created voids.  One thing I learned last year was that it can put down roots anywhere a node comes in contact with the soil.  I will try to limit my efforts on mid-season pulling and burning to when I have something to fill back into the open space or where there are new natives trying to get established.  I will store up my energy for late summer when there is less time for the stiltgrass to regenerate and have enough energy to produce flowers and seeds.

Late Summer and Fall

This is a time when you can make a significant dent in the amount of seed that is produced for next year with the least effort.  Pulling stiltgrass that is 3+ feet tall in late summer will remove a huge amount of potential seed.  It’s also easier on the back than pulling shorter plants.  Timing is important.  It should be done early enough that any seed present on the plants will not be able to mature and late enough that and remaining fragments of plants won’t have time to recover and put up additional flowers.  Here in the mid-Atlantic August is about the right time for that. 

If you find yourself pulling stiltgrass later in the season after seeds have started to form you will need to be more careful about disposing the pulled grass.  You don’t want to risk spreading any seed around.  While I knew that stiltgrass has flowers hidden within the stem, I had not realized until last year that there may be flower stalks buried in nearly every leaf node of a healthy stiltgrass stem.  That is a lot of potential seed!

By my index finger you can see one of the flower spikes
 that was hidden within the stem.  These are able to
self pollinate and produce seed without ever opening up.

Cutting or mowing close to ground level is most effective at this time, too.  Burning with a torch at ground level (when safe and where allowed) is also effective.  I’m not certain, but there is a possibility that some cuttings or unburned stem parts may reroot if they contact the soil under favorable conditions.  I will often rake up the cuttings and put them in a separate pile where they can decompose without mixing in with other materials.

In years past I have spent a lot of time in the late summer and early fall raking stiltgrass out of the lawn.  This was probably of little use since much of the stiltgrass had probably developed seed by then.  Last year I combined raking with overseeding with cool season turf grasses.  The hope was that the cool season grasses would germinate quickly and fill in the gaps left from the stiltgrass.  That should work, in theory, but I can't comment on the results.

So the plans are in place and it's almost time to get started!