Exotic Pest Plant of the Year

by Marc Imlay and Eric Brewer

An alien invader is spreading like wildfire through the parklands of Maryland and Virginia. Japanese stiltgrass (Microstegium vimineum) is a dense, mat-forming annual grass that roots at nodes, is shade tolerant, and occupies various habitats including creek banks, floodplains, forest roadsides and trails, damp fields, and swamps. It is very aggressively displacing our native plants. Several parks have already lost half their flora, along with several birds that depend on native vegetation as part of their supporting ecosystem. If we can lick this one, we can lick most of them.

Japanese stiltgrass is native to temperate and tropical Asia. It can be identified by its lime-green color and a line of silvery hairs down the middle of the 2-3" long blade. It was introduced near Knoxville, Tennessee around 1919, and its current range is from Mississippi to Florida and north to Arkansas, Kentucky, Ohio, NewYork, and Connecticut.

In the last couple of years at Ruth B. Swann Park in Charles County, Maryland, where the Sierra Club and the Maryland Native Plant Society have been sponsoring invasive plant removal events, we have seen Japanese stiltgrass move in with a vengeance, covering over half of the lower areas of the park with a green carpet from early spring to late fall. On the first two weekends in October of last year, thirteen volunteers ranging in age from 23 to 67 worked a total of 104 person/hours in a successful effort to stem the invasion. Together with the work done the previous year, we estimate that 90% of the park's stiltgrass has been killed before it had a chance to set seed.

Our control of Japanese stiltgrass may be a model for the mid-Atlantic region on how to do it right. In areas where the stiltgrass had formed a monoculture, we used a 2% solution of RoundUp applied with a back pack sprayer, staying 10 feet away from streams. Used this way, RoundUp does not migrate, and it biodegrades quickly. Where the stiltgrass plants were mixed with native plants (about 5% of the population), volunteers hand-pulled the stiltgrass. Thus, volunteers were critical to the success of this invasive plant removal project. As more government money becomes available for invasive species control, it becomes tempting to depend on indiscriminant herbicide application by a few trained professionals. At Huntley Meadows Park in Virginia, $12,000 was spent recently on controlling Japanese stiltgrass with herbicide applications. Volunteers at Swann Park made it possible to control an aggressive invader at a cost of $200, while sparing closely-growing native plants.

A goal for the year 2000: Let's control Japanese stiltgrass in Maryland! q

Contact: Marc Imlay
301-283-0808 (h)
703-607-7989 (w)

BOX SCORE 200 acre Ruth B. Swann Park - November 1999
BOX SCORE for 200-acre Ruth B. Swann Park--November 1999
English Ivy 19/88 12 July 98 100% pull/wet
Mile-a-minute 3/6 August 98 100% pull
Vinca minor 31/172 26 Sept 98 99% pull & bag
Ponceras trifoliata 1/1 August 98 100% hack & squirt
Japanese stiltgrass 2/30
July-Oct 98
Sept/Oct 99
20% pull/spray
70% pull/spray
Beefsteak plant 12/55 Oct 98/99 90% pull & bag 
Chinese day lily 2/5 Oct 98 99% dig/quarantine
Garlic mustard 12/48 2 May 99 50% (2nd year only)/bag
Ailanthus (Tree of Heaven) 12/16
July/Sept 99
7 Oct 99
20 % pull
30% hack & squirt
Wineberry 11/44 5 Sep 99 80% pull/wet (spading fork)
Multiflorra rose 11/22 July-Oct 99 10% pull/spading fork
Chinese privet 5/5 Sept 99 5% pull/spading fork/h&s
Lespedeza cuneata 5/5 5 Sept 99 5% pull/wet/spading fork
Japanese barberry 3/2 Oct 99 5% pull/spading fork

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Chesapeake is a publication of the Maryland Chapter of the Sierra Club.