2020 Stiltgrass Wrapup

As we are coming to the end of stiltgrass season for 2020 I wanted to review what I’ve learned about controlling this invasive species on my Mid-Atlantic property over this year. 

Pulling 
Pulling Japanese stiltgrass, Microstegium vimineum, is an effective means for controlling this annual grass, but it is extremely labor intensive.  While its primary germination period is mid-spring it does continue to germinate into summer, particularly if more openings appear in a previously shaded area.  So you may find that you need to redo areas in late summer that you thought had been taken care of earlier.  This was the case in a shaded woodland where I thought I did a pretty good job clearing the stiltgrass at the end of July.  When I returned to that place in mid-September it was in need of more pulling.  Apparently I left enough scraps around that they were able to regrow.  So if you only want to pull stiltgrass once in a season get every bit out the first time, or wait until just before it goes to seed, maybe early September (depending on local conditions) and then pull out all that you can. 

This was the initial condition, before any clearing in 2020.

This was after clearing in late July, by September this area was
overgrown again with stiltgrass.  This time it only took about 10 minutes
to clear the area.  The underlying Rosey sedge, Carex rosea, still looked good.

While searching for more information about the cleistogamous seeds in stiltgrass (those seeds hidden in the stem), I found a Master’s thesis by Samantha Nestory of the University of Delaware.  There it was noted that Japanese stiltgrass grown in sunnier locations had more cleistogamous seed than in shade, 47% vs 28%.  It also pointed out that, at maturity, there is a cleistogamous flower stalk at nearly every joint along the stem. After reading this I checked out some of the stiltgrass that was ripening.  Sure enough, nearly every joint had a flower stalk hidden or nearly hidden within.  In the woodlands I did not find as many of these hidden flower stalks.  Another observation about JSG is that it is able to put out roots wherever a leaf node, or joint, touches the ground.  By this means a single stiltgrass seedling can cover a large area.  Also residual fragments can quickly reestablish.  I’m not sure what this means for stiltgrass that is pulled then dropped back on the ground.  Will it reroot? 

Next to my finger you can see the flower stalk that was hidden under the leaf sheath. 
In sunny locations by early fall there can be one of these at each joint.

This brings up the topic of how to allocate our most precious resource, time.  While I often dive into some of the most thickly infested areas and rip out the biggest plants, it is actually more effective to begin in less densely infested areas and clear them completely.  After those areas are clear, move on to thicker areas.  The idea is that if an area is totally clear you won’t need to come back to redo it as much.  Whereas while you are battling a thick infestation, the lightly infested area is getting worse and then you end up with twice as much heavily infested space. 

Here's a small scale example of complete removal of Japanese stiltgrass. 
Ideally, I won't have to come back again this year and can spend my time elsewhere. 

Lawn 
This year I was late on reseeding the lawn.  I didn't get out there until early October.  I typically use a bow rake to tear our residual stiltgrass, then overseed with an appropriate cool season turf grass in mid-September.  (We are near the southern limits of where cool season grasses are preferred.)  Overseeding helps to fill in the gaps in the lawn that would otherwise be filled by more stiltgrass.  By seeding in fall these cool season grasses can get established and not be affected when I apply a pre-emergent herbicide in the spring to kill the stiltgrass.  I should have raked out the stiltgrass much earlier, before the seed was ripening.

Herbicides
I’ve had great success controlling stiltgrass in the lawn using pre-emergent herbicides in early spring.  Most products labelled for pre-emergent use to control crabgrass are effective.  I have noticed that the amount of hairy cress, Cardamine hirsuta, has also been reduced (this is due in part to mowing at least once in mid-spring to cut off the flowers before they can set seed.) While the pre-emergent works very well in the lawn, it is not as effective in the rougher meadow areas.  

In this mini-meadow I have started to use the pre-emergent herbicide Dimension™
to augment pulling of Japanese stiltgrass.  Naturally occurring species that are flourishing
here include deer tongue and purpletop grasses, wingstem (Verbesina alternafolia)
and wild blackberry.  I have also planted in some panic grass, wild bergamot and brown-eyed Susan.

After two years of treatment in small meadow I have opened up enough space to get some more desirable plants established like wild beebalm, Monarda fistulosa, black-eyed and brown-eyed Susans, Rudbeckia sp.,and grasses like Virginia wild rye, Elymus virginicus, and panic grass, Panicum virgatum.  I noted this year that, in addition to a decrease in stiltgrass, the nonnative invasive bull thistle, Cirsium vulgare, was largely absent this year.  This thistle is a short lived annual or biennial species so is susceptible to control by pre-emergent herbicides.  I have been watching for other changes in the species mix because of the pre-emergent treatments.  Since I have put in some black-eyed Susans, which depend on reseeding to survive, I will not use pre-emergent in that area next spring to see if I can get them to come back on their own.  Ideally I would like to build up a strong network of native species that can exclude the stiltgrass on their own. 

I have not been using post-emergent herbicides on Japanese stiltgrass, but they do have their place in the arsenal. I found research that indicated that the use of grass selective herbicide can be effective, without causing damage to non-grass species.  Fluazifop-p-butyl is a selective post-emergent herbicide that can adequately control M. vimineum with minimal effect on the non-graminoid native plant community (Judge et al. 2005b). Fenoxaprop-p-ethyl, is a selective post-emergent herbicide that provides excellent control of M. vimineum and can maintain or even increase cover and richness of native species post-treatment (Judge et al. 2005a, b, Judge et al. 2008, Pomp et al. 2010, Ward and Mervosh 2012).  Fenoxaprop is not effective on sedges or cool season perennial grasses, like red fescue, so that would be a good thing, since there are many sedge species occupying my woods.  However there are also many shade tolerant grasses like bottlebrush grass, deer tongue grass and mannagrasses that could be affected.  So I would be hesitant to use these useless it was in a very targeted fashion.

 Fire
These past few years I’ve been using fire, primarily from a garden torch, to control Japanese stiltgrass.  I’ve found that fire is good for clearing a space prior to planting, but not for clearing without a plan for back fill with desirable species.  In some areas I’ve burned the stiltgrass seedlings in early summer only to have the area recovered with more stiltgrass; mostly from rooted stems coming in from nearby plants. Fire alone is more effective in late in season (August) when there is not enough time for new JSG to germinate and reach maturity.  It can work particularly well if there are well rooted perennials in the area.  These perennials are able to resprout after their tops have been singed off.  Cool season perennial grasses are a good example of these.

Here I used my garden torch to burn away the stiltgrass. 
Then I planted some plugs of switch grass, Panicum virgatum.

This year I also used fire to dispose of late season stiltgrass that was full of seed.  After realizing just how much seed is contained in a stiltgrass stem, I decided that rather than moving piles of stiltgrass around I would burn what I had in a central location.  Fortunately, I live in an area with plenty of space and that allows burning.  The key to getting stiltgrass to burn well is to allow it to dry out.  I allowed my big piles [photo] of stiltgrass to dry about 2 weeks to get it dry enough to burn rapidly,  In all I estimate I had nearly 2 cubic yards of stiltgrass stems plus thatch from where I reseeded.  This was reduced to less than 2 cubic feet of smoldering ash. [photo].  When burning remember to follow all local regulations.  Don’t burn on windy days, keep the flames under control, and have water on hand to put out any unintended fires and dowse the ashes when done.

These piles of ripe stiltgrass, plus some additional thatch raked out of the lawn,
were reduced to a couple of cubic feet of ash.

Native Competitors
A more exciting aspect of stiltgrass control is finding native plants to fill in or even resist Japanese switchgrass.  Many people, myself included, have noted that golden ragwort, Packera aurea, is very effective at excluding JSG.  

In the woods nearby is a large dense patch of mayapples, Podophylum peltatum, a spring ephemeral.  I have noticed that during garlic mustard season (April to June) there is no garlic mustard growing there.  This year I also realized that there was not any stiltgrass there either, even though the ground is essentially bare save a few sedges and Virginia creeper, once the mayapple has retired for the summer.  I recently saw a post on Facebook where there was a patch of wild ginger, Asarum canadense, that was relatively free of JSG.  These two species spread extensively by rhizomes.  May there’s something to that?  

In early through spring the area circled is covered with mayapples. 
This dense cover seems to have excluded both garlic mustard and Japanese stiltgrass.

There are also grasses that maybe useful.  River oats, Chasmantheum latifolium, grows in dense stands and I have found stiltgrass only on the outer edges.  In the woods the rosy sedge, Carex rosea, has done very well with just a little help from me. In a moist wooded area I noticed that I had an early season grass that excluded the stiltgrass until it went to seed in June.  I’m pretty sure it was a species of mannagrass, Glyceria sp.  (I keyed it out as American mannagrass, G. grandis, but that is a rare species in Maryland, so I will double check when it blooms again next spring.)  In late summer while pulling stiltgrass I came across another patch of grass that had just a very few stiltgrass stems.  Currently unidentified, it seems to block the stiltgrass with a dense layer of thatch from a previous season’s growth.  This is another one to try to identify come spring.

This small, yet unidentified grass seems to have repelled an invasion of stiltgrass.

Next Year:

• Continue with the pre-emergent treatments on the lawn and in limited areas in the meadows.
• Focus my efforts in areas to achieve 'complete' removal before moving on to new areas.
• When burning to clear an area have something ready to fill in.
• Identify those grasses and see what else is holding its ground.

If you have any additional ideas or know of other competitive native species I'd love it if you could share that here!

 

The Forsythia are in bloom, now it's time to...

The blooming of Forsythia is a signal to begin a number of outdoor tasks.  It signals a good time to apply preemergent herbicides for control of summer annual weeds.  I'm giving this a go this year as another tool to get rid of Japanese stiltgrass, Mircostegium vimineum, from my property.  I've been making progress in the woods where I have been pulling it out in July and August as it is getting tall.  Getting it out of the lawn is another matter.  

It's the end of March, and although the Forsythia started blooming
at first in January, I think they are doing it for real now.

There, repeated mowings keep it short and actually induce early seed formation in the lower stems.  I have been raking/combing it out of the lawn in a few areas but that does not seem very effective.  It seems that while I remove a lot of the weed, any remaining stiltgrass just expands to fill in the gaps.  So while I prefer to avoid the used of synthetics, I've tried going it alone for a couple of years and now I need some help.  

Many of the common preemergent herbicides used for crab grass control have been found to be effective on stiltgrass when applied prior to seed germination.  Preemergents that have been shown to be effective include Dithiopyr ('Dimension'), Pendamethalin ('Pendulum'), Prodiamine ('Halts') and Trifluralin ('Preen Weed Preventer').  One of the challenges is finding a preemergent that does not come with added fertilizer.  In my case I do fertilization in the fall, since I am growing mostly cool season grasses, particularly fine fescues, Festuca rubra cultivars.  Fine fescues have low fertilizer demand and I see no good reason to apply fertilizer at a time when weeds are about to take off. The product I found contained only Dithopyr, no excess fertilizer.

Hairy Cress is a winter annual weed that has been taking over here.  Last year I mowed
it early before much of it started producing seed.  This year I'm hoping
 to get some added help from the preemergent herbicide.

As an added bonus this may help control the hairy bittercress, Cardamine hirsuta, that is growing in the lawn.  This weed is a winter annual, sprouting in fall and again in early spring.  While it dies back by mid-spring, this creates gaps in the turf that provides space for the stiltgrass to fill in. 

Dithopyr works by interfering with development of new roots, after seeds have germinated.  Perhaps I should have waited a little longer to put this down in order to allow the existing grasses to get further along, but I didn't want to forget. We'll see how all this works out later in the summer when I can compare treated and non-treat areas for amount of stiltgrass.  Check out this earlier post for some things I tried last fall. 

Securing the Garden Perimeter

Now that all sorts of plants are springing back to life any number of outdoor chores are available, some fun and interesting, others, not so much.  One of the major challenges in last year's vegetable garden was near daily incursions by a plump groundhog.  While we can hope that our resident fox does his/her job, I decided to take steps to modify the perimeter fence to make it more difficult to dig under.

Of course I had read that a good garden fence needs to go below the surface to keep out rabbits and groundhogs, I took the easy way out and only buried  few inches of the chicken wire fence under the mulch.  This was actually partially effective the first year, but last year there were several shallow entrances all around.  One article I read, says to dig a trench 2 feet deep and a foot wide and line the bottom and side closest the fence line with chicken wire.That sounds pretty impressive.  I got started, but hand digging a trench that size was beyond my limits of fun.  I backed off a little and when with 12-16" deep and 6" wide.

Here's some photos of my project:

First, dig a trench.  I used a narrow trenching shovel
to make a narrow hole with pretty straight walls.
This trench was only 14" deep and about 6" wide.

Push in the chicken wire and bend it outwards at the bottom
 so that about 6" covers the bottom of the trench.  This way
if the critter tries to go deeper, it will be frustrated.

Fill in the trench and compact the soil.  Connect the buried chicken wire
with the above ground fencing.  I bent about 6" of the above ground portion
outward to create another digging barrier.

Cover the base of the above ground wire with soil and then
 mulch the area between the inner and outer fence.

So with the inner fence secured against the small mammals I'll need to tighten up the outer wire fence to deflect the deer.  

One of the features of my garden is a pollinator border consisting mostly of native plant species. Since many of these plants are vigorous seeders, I have an abundance of seedlings to move from the garden out to the border.  Before I got started with trench digging I took a close look at the plants I would be digging up to determine with they were keepers or 'weeds'.  Here are some photos of the ones I encountered:

This is an over-wintered rosette of Black-eyed Susan.
It can be recognized, in part, by the soft fuzzy leaves

Black-eyed Susans produce a lot of seed and each plant lives only 2-3 years.  To keep a good supply of these in the border I have been transplanting them out from the inner garden.

At first glance the rosette of the weedy English plantain is similar to the Black-eyed Susan.  

This English plantain has lance-shaped, deeply veined leaves

This clump of common yarrow was dug out of the path of the new trench.

Common yarrow, Achellia millefolium, is a cosmopolitan plant, meaning is occurs in similar habitats on a global basis, not just a single region.  Though not always considered a native species it is very good at attracting pollinators and beneficial insects.

These leaves did not break ground until the last week of March.

Wild columbine, Aquilegia canadensis, is another short lived native perennial and is dependent on reseeding for its long term presence in the garden.  The new leaves are a dark, purplish green and can be difficult to spot until they open up some.  Before the leaves develop they could be mistaken for red clover.

There are a  number of native Cardamine sp.
around but they do not resemble this one

Hairy winter cress, Cardamine hirsuta, is a introduced winter annual.  It develops its foliage in late winter or early spring and is in full bloom by April here.





There are many wild garlics, both native and introduced out in the garden.  Since these have a tendency to deter small mammals, I have not been targeting them for removal.  I planted nodding onion, Allium cernuum, in the garden border a year and a half ago.  I have seen several resprouting, some are already about 6 inches tall.

The foliage of nodding onion is a flattened blade.  The
 weedy field garlic, Allium vineale, found in many lawns
 has darker green tubular leaves

Sheep sorrel spreads rapidly by shallow runners.

The last weed I was tossing out was sheep sorrel, Rumex acetosella.  The leaves of this plant can be used as a tart, lemony flavoring in soups and salads.  The plant concentrates oxalic acid giving them a tart flavor; however, it can be toxic in high concentrations.  I should probably consider trying it in a salad, in moderation.

  

More Winter Trees

Since it is still a little early to start creating the beds for the vegetable garden I've had time to take a closer look at some of the trees out back.  With the leaf buds beginning to swell there is enough information on the twigs to do some identification.  Our new property is blessed with a number of hickory trees.  In my last post I showed a photo of the terminal bud of a Mockernut Hickory (Carya alba).  This past week I found that there were at least two other species of hickories.

The Pignut has smaller leaf scars than the Mockernut.

The first one I noticed had a much more ovate terminal bud than the Mockernut Hickory, and the leaf scars were more like a rounded off equilateral triangle.  Again, I turned to Trees of New York State for help in narrowing down the choices.  Based on the detailed descriptions in the text I feel pretty confident that this one is a Pignut Hickory, Carya glabra.

Not far from the Pignut was another type of hickory.  The leaf scars on this one were triangular with raised edges.  What stands out is the bright yellow buds and the orangy color of the year old twigs.  This one was easy to find in the key since only Bitternut Hickory, Carya cordiformis, has the yellow leaf buds.

Yellow leaf buds and the raised leaf scars indicate that this is a Bitternut Hickory

As I was taking these photos I noticed some branches where the leaf buds were opposite on another on the twig, rather than on alternate sides moving along the twig.  There are only 6 genera of native trees with this opposite branching:  Maples, Ash, Catalpa, Buckeye, Dogwood and Viburnum.  When I see this opposite branching pattern I usually think of maples, but the terminal leaf buds on this branch were not as pronounced as on maples.  To help with this ID challenge I turned to The Tree Identification Book, by George Symonds.  A quick review of the twig photos brought me to this being some type of Ash tree.  I'm pretty sure that this is a White Ash, Fraxinus americana.  I settled on that because the twigs were smooth and not fuzzy (F. pensylvanica); and the leaf scars are concave at the top rather than straight across (F. nigra).

White Ash has smooth, hairless twigs, a blunt terminal bud and the leaf scars are concave at the top (arrow).

 An easy tree to identify in the field is the American Beech, Fagus grandifolia.  In this photo you can see the elongated leaf buds.  Other indicators over the winter are the persistent dried leaves and the smooth gray bark.

Leaf buds of the American Beech 'stick out'.

Looking down at the ground level I had been perplexed by a small leafy plant that was just sprouting up last fall.  I was unfamiliar with it and just assumed that it was badly confused by the warm weather.  As I was deciding on plants to order for this spring I came across a description of a spring ephemeral that matched up with this little plant.  This appears to be Toothwort, Dentaria diphylla.  I will need to keep an eye out for the little 4-petaled white flowers this spring.  I only found one patch, but I hope I have some others.

Toothwort, a spring ephemeral is a member of the Mustard (Brassicacae) Family.

While walking back to the house I noticed a lot of little white flowers blooming in the lawn.  Many aspects of this plant were familiar, but I could not put a name to it.  I ended up digging one up for closer examination with a hand lens.  The flowers had 4 petals so I immediately thought of the mustard family.  I ended up using Gleason and Conquist to key it out as Cardamine hirsuta, Hairy Bittercress.  This is an Old World plant that is now found in 2/3 of the US.  It is a winter annual that germinates in the fall and overwinters as a rosette.  It blooms from early spring and through the summer.  While edible, the leaves on mine are very small, so it would take a lot if picking to make a salad.

Hairy Bittercress has tiny hairs on the leaves and petioles visible with a hand lens.