Japanese stiltgrass or Mircrostegium vimineum has rapidly spread from south to North in Pennsylvania over the last 10 years. This weedy grass is generally considered an invasive species of woods and forests and is particularly common along disturbed forest roads and trails. Although stiltgrass is most commonly found in shady, moist, and disturbed environments, we are seeing it becoming increasingly common on the edges of farm fields and it is invading pasture, hay fields, home landscapes and low-maintenance turf areas. Stiltgrass is an annual that was introduced to the US from China almost 100 years ago. This grass can quickly spread in just a few years and dominate native plant communities and reduce the growth of desirable forages. Whitetail deer and most livestock do not browse the grass which enables it to spread more quickly. Japanese stiltgrass germinates in late April or early May in Central PA and flowers and sets seed in September and October prior to the first frost. It has short broad leaves making it quite distinct from many other annual grasses. In addition, it has a short membranous ligule and hairs on the backside and the upper blade is sparely hairy (see accompanying images).
Stiltgrass control is often difficult simply because it invades areas where weed management is often not practical. In hay and pasture settings, frequent mowing can help suppress the plants, but like many grasses, it is able to still successfully set seed. A number of studies have investigated potential herbicides and glyphosate as well as the grass selective herbicides (Assure, Fusilade, Select, etc.) are quite effective. Seedlings are most susceptible to selective control. Preemergence herbicides that are effective on crabgrass and the foxtails would also be effective on Japanese stiltgrass. However, in hay and pasture settings, few products are labeled for annual grass control making the options limited. An important first step is to recognize the threat of this invasive species and aggressively scout, manage, and monitor its movement and potential to spread.
Japanese stiltgrass seedling (Microstegium vimineum) (Image by Chris Evans, Illinois Wildlife Action Plan, Bugwood.org).
Japanese stiltgrass in its natural habitat (Image by James H. Miller, USDA Forest Service, Bugwood.org).