Grass is Grass, Right?

By K. Bagby VCE Southside Master Gardener I’ll be the first one to admit that grass is not my thing. It wasn’t all that long ago that my mental grass database had about two entries: crab grass and pampas grass, with a possibility of some of those reddish ornamental grasses thrown in, and that other grass that isn’t grass at all (No, not that! The kind with banjos. Bluegrass! Or the lawn grass, I guess). Ignorance was, indeed, bliss. I’ve had a chance to educate myself over the summer about an invasive grass that’s starting to make the news locally, and that’s Japanese stiltgrass. Even so, I hadn’t seen any of it this side of Occoneechee and wasn’t going to get too worried about it yet. Until this past weekend, when my husband and I happened up on a good-sized stand of it not half a mile from the house, and that was just the part we could see. Just like so many other invasive plants or bugs, it’s only a matter of time till I’m staring it down in my own yard. It's actually kind of pretty, if you like that sort of thing. A nice vibrant green that makes a solid but delicate-looking ground cover. So what is it, exactly, and why should we not like it?

The invasive stiltgrass has pale green leaves with a silvery stripe along the middle of the upper leaf surface. The leaves are lance-shaped, much longer than they are wide, up to about three inches long. Photo by K. Bagby Japanese stiltgrass, Microstegium vimineum, is native to Japan, China, and central and southern Asia. Back in the day, dried stiltgrass was used as packing material for fragile items and probably got to the States that way. It was first reported in Tennessee in 1919 and has since spread to most of the Southeast and beyond, from Texas to New England. Stiltgrass is an aggressive opportunist, propagating easily in disturbed soils, such as along roads and drainages, in logged areas or powerline corridors, and places where something such as flood, disease or fire has stripped or damaged existing vegetation. Though it doesn’t spread in full sunlight or areas of standing water, it does well just about everywhere else, favoring moist soils that are acidic to neutral and fertile. It also does well in our Piedmont upland forests. It outcompetes our native plants and grasses, which can trigger a cascade of effects within our ecosystem. For instance, whitetail deer avoid stiltgrass because of its poor nutritive value. They eat more of the native grasses, which in turn gives the stiltgrass more room to expand its footprint. The birds, small mammals and insects that had depended on those native grasses are negatively affected by their loss, so their numbers suffer as well. The larger birds and predators then suffer from the loss of the smaller ones and in turn the largest predators go hungry too. Eventually we arrive at a thriving community of stiltgrass but our native plants, animals, insects and birds are gone. It’s a vicious cycle that will take years to play out, but play out it will unless we can preserve our native flora and fauna. You can find this Asian native on the Virginia Invasive Species list as well as every state contiguous to Virginia. So, what do we do about it? First, learn to identify it. It’s not hard. Stiltgrass is an annual grass that germinates in the spring. It can get as tall as three to four feet if left to do so, though when it gets tall it can flop over. There are nodes along the stem that will grow roots, allowing the grass to grow horizontally as well as vertically. It looks a little like a delicate miniature bamboo, but its stems are thin and wiry. Its leaves are pale green with a silvery stripe along the middle of the upper leaf surface. The leaves are lance-shaped, much longer than they are wide, up to about three inches long. The leaves are a little asymmetric, or very slightly lopsided, and that’s one of the biggest keys for me, since I can easily mistake deer-tongue grass for stiltgrass. Looking at a stiltgrass leaf straight on, one side will be slightly bigger than the other. The leaves are alternate, meaning they grow singly on one side of the stem and then the other, and they’re spaced out along the stem. There are frequently multiple stems to each plant. One of the bonus features is that stiltgrass has very shallow roots and is easy to pull up. Since it’s an annual, it dies back in the fall and won’t come up again. HOWEVER, each plant can produce as many as a thousand seeds. As the parent plant dies back, the seeds drop to the ground. If they’re left alone, they’ll come up in the spring—or in some spring up to five years from when they dropped. Or they’ll get tracked to some new habitat on your boots or jeans or an animal’s hooves or trailer tires or by the wind—you get the idea. Five years of potential viability for every last one of those thousand seeds per plant! How do you even combat such a thing? In small patches, hand weeding or hoeing works well. Don’t compost what you pull up if there’s any possibility of seed in it. For larger invasions, we need something else. Luckily, there are other methods available. The timing is just right for the most effective one. This time of year, roughly from August into October, stiltgrass will be starting to flower and set seed. The flowers are one to three thin stalks at the tip of a stem with the seeds arranged along the stalks (a divided spike-type seedhead, similar to Bermuda grass or crabgrass). The important thing is to not let the stiltgrass set that seed. Cut it down before it flowers. An easy tactic is to mow it as short as you can with the idea that there’s not enough time left in the season for it to mature enough to set seed again. Some people weed-whack it down to the dirt. Keep after it! Stiltgrass can take years to deal with given that the seeds can stay viable in or on the ground for up to five years. Once it goes for several years without being allowed to set seed, it should die out. Other methods of control can include smothering it with plastic or heavy mulch. Different federal and state agencies along with several Extension Services such as NCSU, Penn State, and West Virginia Extension Research are experimenting with different tactics, but your best bet is just to cut it down before flowering and seed development begins. A pre- or post-emergent herbicide can be also used as a last resort, given the collateral damage that could occur to other vegetation nearby and pollinators that may be accidently injured. There’s plenty of information available on Japanese stiltgrass. Virginia Cooperative Extension at https://ext.vt.edu is a good place to start. The U.S. Department of Agriculture’s National Invasive Species Information Center (NISIC) is also full of information. That’s at https://www.invasivespeciesinfo.gov. As is so frequently the case, awareness of the problem is ninety percent of the solution. These invasive non-native plants and insects are a relatively new thing for so many of us, but with our native pollinators—especially bees and butterflies—in danger of catastrophic population failure or even extinction, we’d be well-advised to keep our native ecosystems in mind, and plant and tend accordingly. Many thanks to our Virginia Cooperative Extension Southside Master Gardeners and Virginia Master Naturalists Southern Piedmont Chapter, and to all the people who give their time to and through these groups to educate us! The Virginia Cooperative Extension Halifax Extension Office is open from 8 a.m. to 5 p.m. Monday-Friday. Masks and physical distancing are required. If you have gardening questions, you can continue to reach an extension master gardener or extension staff member by sending an email to wmccaleb@vt.edu or calling the Halifax Extension Master Gardener Help Desk at 434-830-3383. Be sure to give us your first and last name, telephone number and the nature of the call. The help desk phone is routinely checked Monday-Friday. Someone will get back to you, although it may be from a different telephone number.