Management of Microstegium
Microstegium vimineum (Japanese stiltgrass) is an exotic annual grass that was introduced to the southeastern U.S. from Asia in the early 1900s and first identified in Tennessee in 1919. Following a lag period of more than 60 years, it became highly invasive and is now found throughout the eastern U.S. Microstegium is listed as an invasive species in more than 20 states from New York to Florida, from the eastern seaboard to Missouri. It is often found invading along roads, trails, and streams but it can colonize a variety of habitats including sunny, open ridgetops and bottomland riparian areas. It often invades areas that have recently been naturally or anthropogenically disturbed (e.g. windthrows or timber harvests). Once it invades, it creates a seed bank and can require years of management to eradicate. Natural areas managers should be diligent in locating and eradicating new populations.
Species biology and identification
Microstegium employs the C4 photosynthetic mechanism (i.e. it is a warm-season grass) but it is very unusual because it is also highly shade tolerant. Researchers believe that it may be filling an empty niche in eastern deciduous forests where most native grasses are C3 species (i.e. cool season grasses). Microstegium is most productive during the warm summer months when native species are less active. Microstegium germinates in late spring and is relatively small (< 20 cm tall) until mid-June. It can grow to more than 2 m in height although it often falls prostrate and roots at nodes along the stem. It can be identified by its relatively broad, bright green leaves that often form a shallow ‘v’ as they extend from the stem (see photo at right). Leaves also have a faint silver line down the mid-section. Microstegium can be confused with native Leersia spp., Dicanthelium clandestinum, and other species but is distinguished by its growth form: it is most often found in dense patches > 1 m in diameter. Microstegium produces seed in September and October, while most native species produce seed much earlier in the year.
Impacts on native species
Invasions of Microstegium can quickly crowd out native species resulting in significant reductions in herbaceous species productivity and diversity. Invasions also reduce tree regeneration and alter the growth of tree saplings. Microstegium may impact native species through multiple mechanisms including changing soil properties, reducing light availability, and increasing native consumer activity. For example, the amount of vole damage to trees in invaded areas is increased by more than 125%. In addition, senesced Microstegium is slow to decompose, resulting in a dense mat that may inhibit native species recruitment. Fortunately, removing Microstegium with grass-specific herbicides or hand-weeding significantly increases native species productivity and diversity and tree regeneration.
Microstegium often invades very large areas (i.e. acres), so although multiple methods may be used to kill Microstegium, there are few practical techniques. Suggested methods include hand-weeding, mowing, and non-selective and selective herbicides. Recent research has shown that invasions can be successfully removed with hand-weeding, mowing, or selective herbicides but that the recovery of the native community and return of invasions the following season vary greatly among removal methods. Hand-weeding can be effective for small invasions and mowing can help to reduce seed production in flat, easily accessible areas. For large invasions in areas with trees or steep topography, selective herbicides are preferred. Grass-specific herbicides can economically eradicate large invasions, prevent re-invasion the following year, and allow native species to recover. Fluazifop-P-butyl (12 oz/ac; Fusilade DX; Syngenta Crop Protection, Inc., Greensboro, NC) mixed with a nonionic adjuvant surfactant and applied with a backpack sprayer for example kills more than 99% of standing Microstegium and prevents recolonization of sites the following year. Removal of Microstegium with this method results in increased native species productivity and diversity, including more than 120% increase in native tree regeneration. Other grass-specific postemergent herbicides have been shown to have similar effects.
Various online and in-print documents have recommended fire, preemergent herbicides, and non-selective herbicides such as glyphosate to remove invasions. However, preemergent and non-selective herbicides inhibit native species recovery and not enough information is known about the interaction between fire and Microstegium population dynamics to know if fire might be a feasible management tool. Therefore these methods are not currently recommended for controlling Microstegium invasions.
Methods for controlling Microstegium invasions
|Fire||NO||Not currently recommended; more information is needed to determine if properly timed fires might help control invasions|
|NO||Results in damage to native species; equally effective selective herbicides are available|
|Grass-specific herbicides||YES||Mix 22 ml herbicide with 15 ml of surfactant and apply at 40 psi with a backpack sprayer*|
|Hand-weeding||YES||Practical only for very small invasions, must be repeated throughout the season|
|Mowing||YES||Can be used late in the season when plants begin to flower but before seed has matured; must be repeated yearly|
|Pre-emergent herbicides||NO||Effective at eradicating invasions but prevents establishment of native species|
|*Grass-specific herbicides include those with the active ingredients fluazifop-P-butyl, sethoxydim, or fenoxaprop-ethyl. Recommendation above is for fluazifop-P-butyl; check labels for proper application rates and regulations. Generally, Microstegium is effectively killed at much lower application rates than what is recommended on labels.|