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. |
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.
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.