Microstegium on the March

by Andrea Laine, EMGV

Typically I don’t get riled up about weeds that are easy to pull up by hand, but Japanese stiltgrass (Microstegium vimineum) is a HUGE exception. Despite its fibrous, shallow root system, in just three to five years this invasive species can overtake a natural area, pushing out natives and non-natives alike. It is also detrimental to ground-nesting birds and can contribute to fueling forest fires. I’ve observed more and more of it in local forests and parks where I hike as well as the roadsides in my woodsy Durham County neighborhood. It’s a sad sight, especially on conservation lands.   

This spring was the first time I noticed stiltgrass at a friend’s home in the Piedmont region of Virginia. Normally when I‘m there I’m grousing about periwinkle (Vinca minor) and winged burning bush (Euonymous alata), two other invasive species which I have previously blogged about. I admit to feeling a bit of poetic justice at the sight of the one invasive (periwinkle) being overtaken by another (stiltgrass). But the feeling was fleeting. Every subsequent feeling has been more along battle lines – how can I fight this?

A trio of invasive species is pictured here: winged burning bush in the background, a wide mat of periwinkle established in the foreground and now Japanese stiltgrass has joined the scene. Photo taken June 22, 2019 by A. Laine

Identification

Before attempting to eradicate any weed, you want to be sure you have identified it correctly. When I first noticed stiltgrass, its structure and wispiness reminded me of bamboo, albeit a tiny version.  

In plant ID lingo stiltgrass is a “prostrate to erect, sprawling and freely branched summer annual with spreading stems that root at the nodes … Leaves are rolled in the bud; ligules are short membranous with hairs …”1  If you’re thinking, hey what IS a ligule? Don’t despair! Stiltgrass does have one distinguishing characteristic that you need not be a botanist to recognize:  Each leaf on stiltgrass has a silvery midvein that divides the leaf unevenly

Note in the accompanying photo gallery how this feature is absent from other plants (some weedy, some not) that are often mistaken for stiltgrass.


The root structure of stiltgrass is also distinct from other weeds often mistaken for stiltgrass as noted in these photos. (Stiltgrass is the photo with the brown background.)


Growth habit and lifecycle
Japanese stiltgrass seeds germinate in early spring. The plants grow and strengthen through the summer. In June the Virginia patch was about six inches high; At the beginning of August, the plants were two to three feet tall. In NC it flowers from mid-September through October and soon after flowering the seeds are dispersed – 1000 seeds per one wispy plant! Seeds stay viable in the soil for four years.

I consulted a lot of sources before writing this post and it seems that there is not one “right place” for stiltgrass to thrive. Some sources advised sun, others shade. Some moist woodland, others dry roadsides. Apparently, it is adaptable to a variety of conditions. It will even tolerate a mild frost. And, it really makes its presence known in areas where the soil has been disturbed. This may have been a factor for the Virginia property I referred to earlier as several very large trees were felled, cut up, and carted away from the land over the last year. That kind of activity definitely disturbs soil and surrounding environment.

Would you believe there is a tree peony in the midst of this mess of Japanese stiltgrass? Photo taken August 4, 2019 by A. Laine

Understanding the lifecycle of a weed or any unwanted plant is important because in order to stop it from spreading you need to stop it before it seeds. The flowerhead on stiltgrass though is quite small as are the seeds, so best to act based on the time of year than on a visual. From now through September is a good time for those of us in Durham County to act.  

Tactical solutions
Here are three ways to combat a stiltgrass invasion. Which tactic you choose will depend upon how much stiltgrass you have, where it is growing, and your comfort level with chemicals.

Hand-pulling or digging
While this tactic is typically my go-to for weeding, it only makes sense with small infestations and even then, there are some caveats. When we pull weeds by hand, we disturb the soil which is often enough to bring previously dormant seeds to the surface where they will receive the sunlight they need to germinate. “Hand-pulling of stiltgrass plants needs to be repeated and continued for many seasons until the seed bank is exhausted.“2

Mowing
If stiltgrass is growing in your lawn (or what passes as your lawn) then mowing seems like an obvious tactic. But when stiltgrass is mowed too early in its lifecycle, the roots re-energize and send new shoots above ground more quickly than the first time and it may flower and seed earlier, too.3  If possible, delay mowing stiltgrass until the end of August to deter regrowth or seeding.

The best way to prevent stiltgrass in a lawn is to follow best practices for lawn seeding and care. To learn how to properly maintain your lawn consult Carolina Lawns: A Guide to Maintaining Quality Turf in the Landscape

Herbicide
My friend has given me complete freedom to attack the burning bush and the stiltgrass around his home, but not the periwinkle which he likes very much. After three decades it is as much a part of his mountain retreat as the cabin it surrounds. Knowing I needed to save the periwinkle, I turned to the one-percent solution. This is a tip I received from a weed control expert at a local botanical garden during an educational class. (We master gardeners need to complete at least eight hours of education each year.) Extension programs also endorse this solution.

A half to one-percent solution of glyphosate will kill Japanese stiltgrass without harming the other plants around it. Ready to spray containers of glyphosate I have purchased held an 8% solution. Concentrated varieties were 18%. I share this information to drive home the point that more IS NOT better. I suited up (long pants, long-sleeved shirt, tall rubber boots,  nitrile gloves) before mixing up a much diluted version of the herbicide and I sprayed the stiltgrass.  

Do not use glyphosate on your lawn. Pre-emergent herbicides for crabgrass are recommended for preventing stiltgrass from growing in a lawn. These are best applied in late spring or early summer so that the lawn has time to recover.

Weeding is a commitment
Whichever method you choose, plan on at least a five-year commitment. Since I don’t live on or near the property I treated, I won’t know the outcome of my effort until the fall. But I already understand that my work is not finished. I was working in a natural area on a mountain side. I could not reach all the stiltgrass. Hopefully, the patch of stiltgrass growing on your land is smaller, more easily accessible and responds to your chosen method of treatment.

Footnotes
1 and 2 –  Detail about the identifying characteristics of stiltgrass and list of herbicides specifically labeled for stiltgrass: https://content.ces.ncsu.edu/japanese-stiltgrass-identification-and-management#

3 – Control options for grasses and grass-like plants:  https://www.invasive.org/alien/pubs/midatlantic/control-grassesandsedges.htm

Additional Resources & Further Reading
Carolina Lawns: A Guide to Maintaining Quality Turf in the Landscape
https://content.ces.ncsu.edu/carolina-lawns

A very good weed key:
https://weedid.missouri.edu/weedinfo.cfm?weed_id=173

Invasive Plant Species Management, Quick Sheet 4: Japanese stiltgrass, Penn State

Invasive Weeds of the Appalachian Region, University of Tennessee Institute of Agriculture.

Give Your Lawn Love in February

Give Your Lawn Some Love

If you have a fescue or other cool season lawn**, February is the time to give it some love in the form of fertilizer. Turfgrass experts at NC State University recommend applying 1 pound of nitrogen per 1000 square feet of lawn. If you have the results of a recent soil test, use those recommendations instead.

10-10-10-web

The following example calculations from Turffiles.ncsu.edu demonstrate how to use the label on your bag of fertilizer:

To determine the amount of product required to apply 1 pound of nitrogen per thousand square feet, divide 100 by the first number on the fertilizer bag.

Example 1:

A 16-4-8 fertilizer. Dividing 100 by 16 = 6.25 (100/16 = 6.25) pounds of product applied per thousand square feet to deliver 1 pound of nitrogen.

Example 2:\

A 10-10-10 fertilizer. Dividing 100 by 10 = 10 (100/10 = 10) pounds of product to be applied per thousand square feet to deliver 1 pound of nitrogen.

Cool season lawns should be fertilized on or around three holidays – Valentine’s Day, Labor Day, and Thanksgiving. Do not fertilize tall fescue after March 15.

If your lawn has an abundance of annual weeds such as chickweed or henbit, an herbicide labeled for controlling these weeds in fescue can be applied as well. A weed and feed product can be used prior to March 15. After this date, herbicides without fertilizer should be used if weed control is needed.

If you have a warm season lawn, do NOT fertilize this month. Fertilizing can begin once the lawn turns green.

** Not sure what “cool season” and “warm season” mean? Cool season grasses grow best in temperatures between 65 – 80 degrees F (spring and fall in NC). Examples of these are the fescues, perennial ryegrass, and bluegrass. Cool season lawns stay fairly green during our winters. Warm season grasses, like zoysiagrass, bermudagrass, centipedegrass, carpetgrass, and St. Augustine grass grow best in our summer temperatures between 75 – 90 degrees F. These grasses turn brown when dormant in winter.

-Ann Barnes