Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Life cycle and growth habit
Japanese stiltgrass (Microstegium vimineum) is an invasive summer annual plant. This bright green grass has silver hairs down the center of its short, bamboo-like blade. It grows up to 2 ft. tall. It has a weak and shallow root system.
Roots at nodes; elongates quickly in fall, then produces seeds which stay viable in the soil for many years. Dies back in the fall. Seeds germinate in late winter/early spring. The sticky, tiny seeds can be spread into other areas on the fur and hooves of animals (deer), by water, shoes, and clothes.
Conditions that favor growth
Invades and alters disturbed soils in sun or shade. Tolerates low mowing.
Management of Japanese stiltgrass
In ornamental landscape beds
Prevent plants from going to seed. Japanese stiltgrass can be pulled out by hand easily. Do not compost plants with seed heads.
In forested areas
Hand pulling or using an appropriate weeding tool are the primary means of mechanical weed control in lawns. This is a viable option at the beginning of an infestation and on young weeds. Hand pulling when the soil is moist makes the task easier. Weeds with tap roots like dandelions or have a basal rosette (leaves clustered close to the ground) like plantain are easier to pull than weeds such as Bermudagrass (wiregrass) or creeping Charlie (ground ivy) that spread with stolons or creeping stems that root along the ground.
Chemical Prevention and Treatment in Lawns
Herbicides should be used as a last resort because of the potential risks to people, animals, and the environment. Be aware of these precautions first.
Use a granular (apply with a spreader), selective, preemergent herbicide. Apply a preemergent without nitrogen fertilizer. Look for the active ingredient: Prodiamine (Barricade) or other preemergents labeled for crabgrass control. Apply in early spring (March) before it germinates. It germinates earlier than crabgrass so to prevent Japanese stiltgrass the preemergent needs to be applied a couple of weeks earlier than for crabgrass prevention.
Rainfall or irrigation is required to dissolve the herbicide which is then absorbed into the upper portion of the soil and forms a barrier which kills weed seedlings. Preemergent grass herbicides have residual activity that lasts for several weeks after application. High temperatures and rainfall will decrease the length of time they remain at sufficient concentration to be effective.
Tips for herbicide application:
If planning soil disturbance, such as aeration, do it before application.
Apply prior to seed germination which begins, in early spring a couple of weeks before crabgrass seeds germinate.
Water after application, according to label.
A second application may be possible, usually 6-8 weeks later (see product label).
Consult label for specific waiting period between application and overseeding.
If Japanese stiltgrass is present in your lawn, a postemergent herbicide labeled to control annual grass weeds like crabgrass can be used to spot treat young weeds. Herbicides do not work well on mature plants. Look for the active ingredient Fenoxaprop.
Japanese Stiltgrass | Penn State (2020)
Japanese Stiltgrass Control | Rutgers New Jersey Ag Experiment Station
(PDF) Weeds Gone Wild: Alien Plant Invaders of Natural Areas