Japanese Stiltgrass

The client requested identification of a weed taking over his lawn and recommendations on how it should be controlled.

DIAGNOSIS / RECOMMENDATION

Photo 1

The weed was identified as Japanese stiltgrass (Microstegium vimineum). It can be controlled in lawns using a selective post-emergence herbicide as recommended by Virginia Cooperative Extension in the current Pest Management Guide [1 and see table 5-7].

ADDITIONAL INFORMATION

Japanese stiltgrass is an introduced invasive weed species. First discovered in 1919 in Tennessee (probably in packing material used in crates sent from its native China), it now is found throughout much of the eastern U.S. [2, 3]. Stiltgrass is a weak rooted and sprawling summer annual grass that can grow to heights of 6 feet, though it is usually much shorter. Taller plants typically lie flat along the ground or propped up against other vegetation. Plants usually have multiple weak stems, with aerial rootlets near the base, giving rise to the common name ‘stiltgrass’. The leaves are short with smooth edges and a noticeable silvery midrib on older leaves. [8] The flowers and fruits are borne on thin spikes on the top of a delicate stem. In winter, the thatch is a distinct bright tan to orange color [4]. It is important to correctly identify this species from others that may look similar (nimblewill, whitegrass, smartweed, crabgrass) [4] so that the correct control measures can be followed.

Commonly found in shady, moist areas, Japanese stiltgrass germinates in early spring, several weeks before crabgrass yet flowers and seeds much later, from mid-September through October [5, 6] In residential areas, stiltgrass can invade lawns, landscape beds, and vegetable gardens. Stiltgrass does not proliferate in full sunlight or in areas with standing water [7, 8]

Photo 2

The seeds are small and easily adhere to clothing, shoes and animal fur, which aid the spread of stiltgrass along woodland pathways, lawns and gardens. Unfortunately, deer do not feed on this plant but may open areas for infestation by feeding on competing species. [7]

Control of stiltgrass should begin with sanitation. Since Japanese stiltgrass infestations typically begin in disturbed areas and then spread from those sites, early detection and control can prevent severe infestations. Japanese stiltgrass can produce large numbers of seeds – from 16,000 to 50,000 seeds per square meter. [5] Long-term management programs should emphasize prevention of seed head formation to deplete the seed reservoir. [7, 8] Where necessary, sanitation steps can be supplemented by the proper use of an approved herbicide [1].

In lawns, regular, close mowing reduces seed production. However, mowing once in late summer can be as effective as frequent mowing in reducing seed production. Hand weeding is effective on small infestations but is generally not practical for larger infestations. When flowers are first visible, many seed will mature even if the plants are mowed or pulled. Therefore, mechanical control should be done before flowers are visible. Growing and maintaining a healthy, dense lawn is the best preventative method to discourage the introduction of and growth of Japanese stiltgrass. Proper seed selection, mowing, liming and fertilizing according to a soil test, watering, etc. are all important cultural practices for maintaining healthy turfgrass. [7, 8]

In ornamental beds, hand hoeing and hand pulling can be an effective means to control stiltgrass as long it is done before it has dropped seed. Recognize that hoeing or pulling stiltgrass early in the season (before August) disturbs soil which can stimulate germination of new plants from the seed bank. [7, 8] Stiltgrass is very shallow-rooted and can be easily pulled. Any removed plants should be disposed of carefully and not added to compost, particularly if there are seed heads. [8]