My wife and I have been on a campaign against invasive
plants on our property. Our two main
targets are garlic mustard and Japanese stiltgrass, Microstegium vimineum. The spring time is when our focus is on
garlic mustard, when the ground is soft and before it begins to flower. In late summer our focus switches to
stiltgrass. I am trying to come up with
a program that works for me: how can we eliminate as much stiltgrass with the
least amount of work and without causing too much collateral damage.
|
This is a shady area that used to be mowed. The stilt grass has moved into
the gaps and is crowding out the native vegetation. |
We've been pulling plants from planting beds as they appear
(compulsive behavior), pulling larger plants and weed whacking in late
summer. Recently a friend pointed out
how much stiltgrass was growing in the lawn.
I realized that this lawn weed may be creating a large mass of seed that
could easily recontaminate the surrounding woodlands. So I'm now including the lawn in the
project.
The Plan
As the weather has gotten cooler I could see how stiltgrass
has taken over large swaths of the lawn. This
effectively creates bare spots that are prime territory for stiltgrass to
resprout in the spring. Remembering that
one of the best to control lawn weeds is to have a thick turf, I decided that I
should be more aggressive about filling in those bare spots with desirable
plants. My general plan is as follows:
- Pull in early August.
This allows a second crop to germinate, but not enough time to mature
before frost.
- In natural areas minimize disturbance to soil and encourage existing native species. Cut stiltgrass low when flowering starts, about mid to
late August to early September.
- In disturbed areas (lawn) try to add more competitive ground
covers, like cool season grasses to get established before stiltgrass germinates in
mid-April (WVa).
This will be a 5+ year program to get rid of the current crop of seeds already in the ground. There will be continued outside
pressure from surrounding areas infested with stiltgrass.
|
Japanese stiltgrass is turning brown in the lawn early October.
This thatch can be slow to break down,
leaving a gap for more to germinate in spring. |
In late fall and winter stiltgrass appears as a persistent golden-brown thatch. The usual invasion route is into areas of disturbance
in an otherwise natural space. Deer are
also vectors for the spread of stilt grass.
They often bed on top of stiltgrass infested areas, then carry the seed
with them, dropping it along their paths.
While they will sleep on stiltgrass, deer do not feed on it. Instead they feed on native vegetation,
further helping stiltgrass to outcompete native species.
In late August/early September a flush of growth is a signal
that stiltgrass is maturing and seed production is about to commence. Waiting to cut the grass at this time does
the maximum damage to its reproductive cycle.
Early season mowing or whacking of stiltgrass stimulates early flowering and
a lower, harder to remove growth habit.
Pulling stiltgrass early in the season creates openings that allows
additional germination. By waiting until
late in the season these late germinated seedlings will not have time to mature
before they are killed by the colder temperatures. I really like the idea of tricking it into germinating late in the season. Also plants pulled out before the seed has matured can be left to decompose. After the seed has ripened in mid- to late-September plants should be bagged and landfilled to prevent spreading of the seed.
I found this recommendation by West Virginia forester,
RussAnderson:
"If the area where stiltgrass
control is desired includes a lawn that is infested, all regular mowing of that
portion of the lawn should cease around July 15 and allowed to grow for a month
before mowing again. Normally, during this 30 day period the stiltgrass will
significantly outgrow all other lawn
cover making it both easier to identify and easier to kill. To ensure the
highest proportion kill possible in the stiltgrass the best option is to mow
the lawn, especially where the stiltgrass is present at the lowest blade
setting. Completing the mowing during the hottest and driest conditions
possible will further enhance the kill in the stiltgrass. If the mowing of the
lawn is successful, regular lawn grass will begin to fill in the dead spots
almost immediately. If the stiltgrass is mowed before it is allowed to go to
seed the number of stiltgrass seedlings on the lawn will greatly decline in
succeeding years."
It's hard to leave an area of lawn unmown. But if this works, consider all the labor and
chemicals saved compared to removing stiltgrass by other means. Also this can be a positive step by NOT doing
something (mowing for a month), rather than continually mowing.
|
Here's that same shady area after weed whacking and raking up the cut stiltgrass (upper left). Pink flags indicate the location of desired native species left in place. |
Weed whacking stiltgrass from hard to mow areas should be
done in this late August period. Cutting
as low as possible removes both the upper flowers as well as the lower
cleistogamous
flowers hidden in the stems. If there
are native species going to seed in the area, waiting until they mature can
help reestablish native populations. In
some smaller areas I surveyed for native species and flagged them so that they
could be avoided while whacking the stiltgrass.
Cool season turfgrasses
|
Since each fescue plant is so small the seeding rate
is fairly high, 5 lb/1000sf, to get good coverage. |
Tall fescue is a good choice for high traffic sunny
areas, but this is not a North American species. Since my focus is on using native vegetation
and natural appearance, I am using a
mostly native fine fescue blend. (Eco-grass from Prairie Moon) of red and
creeping fescues for the shadier areas.
In the wilder areas I am trying a blend of native grass species. This is an experiment to see if I can get
good cover with these prairie species used in a lawn-like environment. However, a prairie is managed much differently than a
lawn and there is a good chance that this approach will not be successful. Many of these native grasses need
a year or two to put down roots before top growth takes off. Ideally these species should be allowed to
mature for a season or two before they get chopped back, by mowing or grazing.
For sowing, I first used an iron rake to clear out the stiltgrass thatch. (Looking back, if had done this in early September I could have limited the stiltgrass seed production even more.) This also loosened the soil surface. Then I broadcasted the seed. Finally I used the flat edge of the rake to push the seed in closer contact with the soil. To get good germination and establishment of the seedlings the ground should be kept moist. I usually try to time fall seeding with the weather forecast to take advantage of rainfall to get the grass started.
|
About 10 days after seeding with Eco Grass a fine green haze is covering this previously barren area. |
Most commercial turf grass blends contain annual and perennial ryes which are fast growing and fill in quickly. The fine fescues used here do not grow as quickly and it will take longer to have that full look.
Native Grasses
With that in mind I decided to try this as an
experiment. I selected species that
tolerate grazing, where they would be eaten back to 3-5 inches, since mowing it is a similar action. Since I am fall sowing
I selected mostly cool season grasses, with the hope that they will get
established before the stiltgrass germinates in the spring. Also, there are warm season species in the mixture to try and
fill in the gaps when the weather warms. The grasses I selected where mostly native to
Maryland or the mid-Atlantic region.
Name
| Botanical Name | |
Season
|
Exposure
|
Seeds/pound
|
Sun mix ratio
|
Shade mix ratio
|
Canada rye
| Elymus canadensis
| |
cool
|
Part
|
100K
|
8
|
4
|
Virginia rye
| Elymus virginicus
| |
cool
|
Part
|
100K
|
4
|
2
|
Side Oats Grama
|
Bouteloua curtipendula
| |
warm
|
Full
|
150K
|
6
|
1
|
June Grass
|
Koeleria macrantha
| |
cool
|
Full
|
2000K
|
1
|
0
|
Fall or Beaked Panicgrass
|
Panicum anceps
| |
warm
|
Part
|
--
|
0
|
1
|
White clover
|
Dalea candida
| | -- |
Full
|
260K
|
4
|
0
|
I made up two seed blends one for full sun and the other for
part shade. The majority of the seeds are cool season grasses. The weight ratios for each are listed in the table above. When making up a seed blend
you need to account for the number of seed per pound and the seed viability,
usually listed as pure live seed (PLS) which is seed purity times the germination
rate. This is my first time trying this
so I can't be sure that it will work. I
did put some seed into a new meadow area that will not be mowed regularly. This will serve as my 'control' group.
A better way to sow these native grass seed would be to use a seed drill and put them in 1/4 to 1/2 inch deep. Instead, I sowed them the same as I did for the fine fescue, but at a much lower rate (pounds/sf). The recommended rate for Eco Grass is 5 lbs/1,000 sf while for Canada rye it is on the order of 3 oz/1,000 sf. Since the ryes and other native grasses are much larger plants when mature, compared to a single fescue plant, it takes only a few seeds to get the same coverage.
|
June grass has a seed similar fescue is size;
however, the resulting plant is much larger |
|
Side oats grama has a lot of husks included, but
these are accounted for in the PLS calculation |
|
Virginia and Canada ryes look similar. |
If I don't see sufficient germination by next spring I will go back to a standard turf grass blend. It's better to fill in with something than leave space for stiltgrass.
|
15 days after seeding I'm seeing some new grass growth in some of the sunnier areas. The shade areas are not showing definitive signs of new grasses. |
|
We were surprised to find this obedient plant
blooming late in the season. I don't know if this is indigenous
or if it escaped from an earlier planting by a previous landowner. |
Other strategies
Broad spectrum (glyphosphate) and grass specific herbicides are effective on stiltgrass, but they may impact surrounding vegetation. I found a
mention of using a dilute solution of Fusion® (grass specific herbicide) to kill stiltgrass with relatively little collateral damage to native perennials and grasses. Another tool is the use a preemergent herbicide in spring. However, since stiltgrass continues to germinate throughout the spring and summer, a single treatment alone would not be effective. A preemergent would also suppress germination of other desired species.
One of the side benefits while pulling stiltgrass is that it gets you looking closely at plants and nature. We've spotted a number of interesting plants this year while thinning out the overgrown edges of the woodlands. Most recently I spotted a dark pink Obedient Plant among the grasses.
References
The following are some additional websites with useful information on dealing with Japanese stiltgrass: