Friday, August 28, 2015

Stiltgrass is in bloom - The time to act is now!

The flower heads of Japanese stiltgrass are just opening up.
The weedy plants have just had a growth spurt
bringing some of them to nearly 4' tall.
I am in midst of a multi-year battle to get rid of, or at least control, the Japanese stiltgrass, Microstegium vimineum, on our property.  Last year I came up with a plan to bring this invasive species under control.  The key element is to prevent this annual grass from setting seed.  Eventually (5-7 years) the seed bank will be depleted.  Also I am encouraging the existing native plant population to back fill the gaps to suppress re-invasion.

In late August stiltgrass goes into a growth spurt as the flower heads develop.  It is critical to cut it down or pull it out before seed set begins.  By killing the plant before the seeds can mature, you can dispose of the plants by composting.  Otherwise the plants would need to be segregated (e.g. bagged and sent to landfill) to prevent another generation of seed from spreading.  The taller stiltgrass is easier to find and pull than it is earlier in the season.  You should try to remove the plant close to the ground since it also produces a second hidden (cleistogamous) flower in the lower stem.

The following two photos show a moist shady area just before I removed the stiltgrass.

One year after close cutting stiltgrass in late August (2103) the growth is still rather dense.

After two years of cutting there appears to be more gaps in the stiltgrass converage.

In a couple of areas I was weed whacking and composting in place.  After 2 years of this I am seeing some minor decreases in the density of the stiltgrass coverage.  This year I raked the cut grass off and into a pile.  By removing the dense thatch I am hoping to seed some other species move in.  I have another large area where I will leave the cut grass in place.  We'll see if that makes a difference.

American germander blooms in late July and the seed is still maturing,
so I'd like to keep these standing a little longer.

One of my challenges is to remove the stiltgrass while leaving as much native vegetation in place.  Many of the earlier blooming natives, such as the beebalms (Monarda sp.) and tick trefoils (Desmodium sp.) have already gone to seed.  However, there are a number of later blooming species that I'm trying to preserve by carefully hand-pulling around them.  These include American germander, (Teucrium canadense), Virginia knotweed (Persicaria virginiana), white vervain (Verbena urticifolia), white avens (Geum canadense), and the native annual, clearweed (Pilea pumila).  While not beautiful plants on their own these species do fill the woodland edge with a variety of colors and textures largely obscured by the invasive stilt grass.

Clearweed is a fairly common native annual found in shady moist sites.
Currently in bloom, the flowers are yellow tassels in the leaf axils.

Here I'm halfway done with a section revealing some American germander (center).  To the left is my new grass whip.
I recently got a double edged grass whip which does a great job of ripping stiltgrass out of the ground while leaving single bladed grasses largely intact.

This low-growing sedge was hardly disturbed as the weed whip tore out the stiltgrass.

I am also finding a number of native grass species under and within the stiltgrass.  These include the evergreen, spreading sedge (Carex laciculmis) and deer-tongue grass (Dichanthelium clandestinum).