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.

Learn With Us, week of July 7

Canceled: PESTS – For Garden’s Sake Nursery Saturday, July 13, 2019 10:00 – 11:00 am

For Garden’s Sake 9197 NC-751, Durham, NC 27713

Managing PESTS in your yard & garden. Integrated Pest Management (IPM) is a research-based process you can use to help solve pest problems while minimizing risks to people, useful critters and the environment. Topics covered will include identifying some common local pests and how you can use the 5 major principles and practices of IPM to help maintain a healthy and happy landscape.

Free/Registration required
To register, email ann@fgsnursery.com or call 919-484-9759

Scouting for Insect Pests, June Edition

Squash Bugs

squashbugweb

Photo: growingsmallfarms.ces.ncsu.edu

Squash bugs, which have overwintered as adults, are actively laying eggs now. Egg clusters can be found on the undersides of leaves. Remove and crush the eggs to reduce the population of squash bugs.

squash_bug_eggs
photo: Whitney Cranshaw, Colorado State University, http://www.insectimages.org

Nymphs and adult squash bugs suck sap from plants and can quickly destroy squash vines. Adults and nymphs frequently hide under damaged leaves and at the base of plants. Keeping debris and mulch away from the base of plants reduces cover for the bugs and may also reduce damage. In fact, Clemson University suggests the following method of trapping adults and nymphs: “The secretive nature of squash bugs can be used to your advantage in controlling these pests. Place a small, square piece of old shingle or heavy cardboard under each squash plant. As bugs congregate under it for protection, simply lift the trap and smash them with your hoe (or shoe).”

http://www.clemson.edu/extension/hgic/pests/plant_pests/veg_fruit/hgic2207.html
http://www.ext.colostate.edu/pubs/insect/05609.html

Mealybugs

mealybug

Photo: ucanr.edu

These pests can be a problem on ornamental plants in the landscape as well as on houseplants. Female mealybugs are oval shaped, soft-bodied, wingless, and covered with a fluffy wax. Males are gnat-like and have wings and a waxy tail. Eggs are contained in a fluffy, waxy mass. Mealybugs feed on sap from plants. They excrete waste called honeydew, which promotes the growth of sooty mold. Small infestations can be controlled by wiping away the insects with a cotton swab dipped in isopropyl (or rubbing) alcohol or nail polish remover or with insecticidal soap.

http://www.ces.ncsu.edu/depts/ent/notes/Ornamentals_and_Turf/flowers/note19/note19.html

Spotted Wing Drosophila

 

on-raspberry-1024x730

Photo: Jesse Hardin, North Carolina State University

The Spotted Wing Drosophila damages fruit crops by cutting a slit into healthy fruit and laying eggs inside. Spotted Wing Drosophila prefers softer fleshed fruits like berries, cherries, and grapes. These insects are less than 4mm in length, and their larvae can be found inside fruit, causing softness and holes.

How can I manage SWD (Spotted Wing Drosophila) in my garden?
While SWD infested fruit may be unpalatable, larvae are not harmful if consumed. Ripening and ripe fruit are susceptible to SWD attack, but flies do not appear to be attracted to unripe fruit. Good cultural management can reduce SWD damage. Good cultural control includes:
1.Excellent sanitation: fruit should be harvested frequently and completely. Any unmarketable fruit should be removed from the field and either frozen, “baked” in clear plastic bags placed in the sun, or hauled off site to kill or remove any larvae present. When you done harvesting for the season, strip any unwanted fruit from plants and destroy it.
2.Canopy and water management: Prune plants to maintain an open canopy. Do not overwater plants. Leaking drip irrigation should be repaired, and overhead irrigation should be minimized.
3.Exclusion: Fruit can be covered with fine mesh bags or paint strainers prior to ripening to exclude flies. Bags should be tightly sealed. Placing a foam plug between branches and the sealed based of bags is useful to prevent plant damage and maintain a tight seal.
4.Regular fruit sampling: Fruit should be observed regularly for infestation before and during harvest.

While cultural control may be sufficient to reduce SWD infestation below damaging levels, insecticides are currently the most effective tool to reduce or possibly prevent SWD infestation. Insecticides can only be applied to plants for which they are labeled. The label is the law! County extension agents and university
specialists can assist with selecting effective, appropriate insecticides. There are some organically acceptable insecticides available for SWD, but they are less persistent than conventional materials and may need to be applied more frequently. (per http://www.ces.ncsu.edu/wp-content/uploads/2013/04/Homeowner-Factsheet-2013.pdf)

http://swd.ces.ncsu.edu/swd-biology/

This video shows how to make a Spotted Wing Drosophila trap to assess the presence of these pests in your garden.

Finally, Japanese Beetles are active. Beetle traps are more effective at attracting Japanese Beetles than controlling them. If you do use traps, locate them far from plants you wish to protect. Per NCSU: Homeowners can take advantage of the beetles’ aggregation behavior by shaking plants to dislodge beetles each morning. Without beetles already on a plant, it is less likely that beetles will aggregate there later in the day. Picking beetles off by hand will also reduce the accumulation of beetles that results in severe damage. They can be easily knocked into a widemouth jar of soapy water.  In some settings, flowers or plants can be protected with cheesecloth or other fine mesh.

http://www.ces.ncsu.edu/depts/ent/notes/O&T/flowers/note44/note44.html

IPM

Are you a fan of Facebook? The national Extension Master Gardener Facebook page has been discussing Integrated Pest Management (IPM) this week. For those who are not familiar with the concept, this definition from North Dakota State University sums it up nicely:

“IPM is a sustainable approach to managing pests by combining
biological, cultural, physical and chemical tools in a way that
minimizes economic, health, and environmental risks.”

I highly recommend the series of posts starting on February 17th to anyone interested in learning more about using IPM practices in their own gardens: EMG Facebook page. For those of you not on Facebook, a call to the Master Gardener office or a web search of NCSU Extension resources (such as the IPM North Carolina website) can provide a wealth of information on the topic.

One of the goals of IPM is to reduce the use of broad spectrum insecticides that harm both the pests and beneficial insects. Scouting for pests is an essential part of management, as opposed to spraying for insects on a schedule regardless of whether they have been found in the garden. This Beneficial Insect Chart can help identify the “good bugs” in your yard – having them around can do some of the pest control for you!

IPM chart

-Ann Barnes