Thursday, October 5, 2017

Progress on Japanese Stiltgrass Removal - 2017

My 4 year long battle with Japanese stiltgrass, Microstegium vimineum, is continuing and it must be a continuing fight to remove this invasive grass from my property.  Since this is an annual grass the goals are to keep it from producing a new crop of seed and to eventually deplete the seed bank so that it won't crop up again from older seed.  Since this grass is all around I will need to take the fight to the neighborhood and beyond.  This will be easier if I can demonstrate to  other that this is a battle that is worth fighting.

One approach to Japanese stiltgrass removal is to nuke the site with round-up or a grass selective herbicide.  Despite it being effective on the current year's growth, this would still be a multiyear approach to deplete the seed bank.  I'd rather not kill everything because I have a number of interesting plants that I want to keep and I am generally opposed to the indiscriminate use of herbicides or pesticides. 

The key to non-toxic approach to stiltgrass removal is good timing.  Pulling the grass in late summer as the flowers are forming (late July to early September in Maryland) is the best time to concentrate your efforts.  Early season pulling helps, but if some plants remain they will expand to fill the void and you will need to return to pull again.  Stiltgrass pulled before seed has formed can be composted, though I usually segregate it from the rest of my garden scraps just in case.   Any grass pulled after flowering should be bagged or at least segregated and covered so that seed can not escape.
Here's a woodland edge area in 2013 when I started pulling/whacking stiltgrass
In 2014 coverage is not as dense, but still dominant.
In 2015 other plants are showing up.  Also I had seeded in some Virginia rye in 2014.
Now in 2017 stiltgrass is no longer dominant.  In the foreground is
Virginia rye, Elymus virginicus, drying out after seeds have matured.  

 The photos above show the progress that has been made over 4 years.  For the first two years this site was weed whacked to near ground level and then raked out.  As the stiltgrass density dropped I switched over to hand raking and pulling for the past two years.  These methods were more selective and allowed me to avoid the more desirable plants that were coming back in.

Mature Japanese stiltgrass, note the
location of the cleistogamous flowers.
In lawns, mowing stiltgrass is done to control its spread.  Unfortunately stilt grass has the ability to form cleistogamous flowers near the base of the stem.  These flowers are enclosed in a leaf sheath about an inch off the ground and can survive most mowings.  It has been reported that these flowers mature earlier in stiltgrass in regularly mown lawns.  To address this Russ Anderson, a West Virginia forester has suggested allowing stiltgrass to grow freely through July and then mow it closely to the ground in August as the flowers begin to develop.  The expectation is that there will be fewer cleistogamous flowers and by cutting it back late in the season there is not time enough for the grass to regrow.  I have been doing a variation of this in an isolated area where I am growing fine fescue.  Instead of mowing, I use a manual grass whip.  This rips out the stiltgrass and leaves more of the fine straight blades of the fescue intact.  After doing this for two years the amount of stiltgrass in the area has decreased, but I still have a few years to go.  

Another technique that I have been using  to remove stiltgrass from the lawn is to briskly rake the lawn after a rain to try and catch the lateral stems (stolons) of the stiltgrass.  Using a spring or bamboo rake does tear out a lot of stiltgrass, but it also tears up the soil and can damage the bunch and perennial grasses as well.  I also found that after doing this in early July, even though I removed a great deal of stiltgrass, much of it had regrown to fill the gaps in the lawn.  Inspection of the stiltgrass at this time did not show evidence of the cleistigomous flowers. 

This area was raked over with a steel garden rake.  Nearly all this debris is stiltgrass.

What appears to have worked better is a stiff steel garden or bow rake that is pulled along the surface of the ground.  It catches and pulls out the stolons of the stiltgrass and since the action is not so vigorous, most of the other bunching grass are left intact.  I did this in mid-September so there is not enough time for the stiltgrass to regrow.  Even though the soil was dry, the stiltgrass pulled out easily.  Inspection of the stems showed that there were some cleistogamous flowers forming at this time.

Areas that are blackened were burned with the torch (next to watering can). 
I kept a full watering can nearby just in case the fire got out of hand (it didn't).  I left a small area
in the middle un-burned as a 'control group'.
These mechanical methods are helping reduce the number of stiltgrass plants in the lawn but there are still a number that escape the raking and pulling.  A new approach that I am trying out this year is fire.  Burning stands of stiltgrass is not effective early in the season while new plants are still germinating, or in the off season when plants are already dead (stiltgrass seed is relatively fire resistant).  However, burning in late summer as the stiltgrass is beginning to flower may be a way to successfully battle a stiltgrass invasion.  This method was suggested to me by Joene Hendry, who writes the blog  Joene's Garden.  The process I am trying is to first mow the area close to the ground (about an inch), then allow a day or two for the grass to dry out.  Next use a garden torch to burn the remaining stems, this should get at those hidden flowers.  While this may seem extreme, any perennial  grasses with good root systems will bounce back in a week or two, but the stiltgass is not able to recover.   I did try burning without mowing first, but stiltgrass holds a lot of moisture and it takes a long time to completely burn up such a moist plant.  Mown plants, without a lot of leaves, were quickly burned up.

Another element of stiltgrass removal is to fill in the gaps with desirable vegetation.  Since I am located in the cool season grass zone I have been using a fine fescue blend (like Eco-lawn) in the shadier areas and tall fescue blends in the sunnier spots.  I do have some zoysia grass growing in the sunnier spots.  This warm season grass grows thickly and excludes most of the stiltgrass.  It's unfortunate that there are not more native options for turf in this area (although red fescue, Festuca rubra, is technically a native species).  By avoiding the use of broad spectrum herbicides I do allow the native sedges, violets and other species a chance to repopulate.

I did get an early start over-seeding this fall and I hope to have the new plants established before it gets too cold.  If these desired grasses get established I will experiment with some pre-emergent herbicides.  These act by  interfering with root development after seed germination.  These are particularly effective on annual species such as Japanese stiltgrass and crabgrass.   I imagine a year without stiltgrass competition should help develop a thicker lawn. 

1 comment:

Unknown said...

I also use a flame torch for weeding at times. From my reading I've come to believe that the plant does not need to completely burned up to be eradicated. It's simply needs to get adequately hot. Theoretically if one can see a thumbprint on the leaf tissue enough damage has been done to kill it.