Nimblewill

Is Nimblewill Ringing Your Doorbell?

Nimblewill (Muhlenbergia schreberii) is a lawn weed that can slowly but surely spread across a weak lawn, giving it a patchy, dull blue-green appearance. Thanks to numerous thin, wiry stolons, it can aggressively invade a yard. Nimblewill is a warm season (C4) creeping perennial grass considered to be native to North America. In the southern states, some even consider it as a shade-tolerant turfgrass species. It has limited value as a forage and is not generally considered to be palatable by livestock.

Cool season grasses, such as perennial ryegrass, Kentucky bluegrass and tall fescue, that constitute the bulk of lawn-type turfgrasses in West Virginia, tend to become semi-dormant during the hot summer months, while nimblewill spreads aggressively during this time due to its ability to tolerate heat. Warm, dry summers tend to favor nimblewill. Contrarily, its inability to tolerate cold temperatures turns it brown during winter months to make it appear as patches of dead straw scattered throughout the lawn, which can sometimes be confused for dead turf. Winter is, however, a good time of the year to scout the yard and prepare your management strategies for the following growing season.

Nimblewill Identification

Nimblewill leaves are flat and narrow, about 1 to 2 inches long, with a few tiny hairs present at the base of the leaf along with a small membrane like appendage (ligule) where the blade hugs the stem. The stems are slim and upright early on but become decumbent with age to produce stolons capable of rooting at nodes. Inconspicuous axillary seed heads about 5 inches long are borne during late summer. Nimblewill can reproduce both from seed and asexually through the stolons. It has a relatively shallow, fibrous root system.

Controls for Nimblewill

Non-chemical approaches are mostly preventative and strictly depend on providing optimal conditions to nourish the turfgrasses to maintain a dense cover. These include choosing the right species (shade-tolerant or sunlight-loving), proper soil pH and other conditions for establishment, appropriate mowing height and frequency, fertilizing the lawn as needed at the proper times of the year, providing adequate drainage and irrigation, and occasional aeration. Among these cultural practices, mowing and fertilization are critical.

Chemical controls comprise of two strategies – using a selective herbicide to treat small areas or using a non-selective herbicide to spot-treat localized infestations or renovate the entire yard. If more than half the lawn appears to be patches of dead straw, it may be a good idea to renovate the entire lawn as opposed to resorting to selective control options.

The only selective herbicide labelled for use on cool season grasses in lawns is mesotrione (Tenacity). Two to three sequential applications at two- to three-week intervals during the active growth stage of nimblewill may be necessary to provide acceptable levels of control. This herbicide can whiten or bleach the weed as it starts to respond, causing large infestations to stand out after being treated. It only takes about one-tenth of an ounce (3.5 ml) to treat 1,000 square feet. Due to this low use rate, one has to be careful to apply the appropriate amount, using a calibrated sprayer. Another selective herbicide, topramezone (Pylex) is labelled for use in recreational and utility types of turfgrasses.

The non-selective herbicide option consists of using the systemic herbicide glyphosate (Roundup and other formulations). Patches can be effectively controlled by spot treatments, whereas large areas may require broadcast applications to treat entire sections. A good application window would be late summer, as long as the soil is not too dry.

Reseed dead grass or bare spots with a suitable turfgrass species in early September and facilitate good contact with the soil for good germination by disturbing or lightly tilling the areas that you will reseed. Apply a mulch after reseeding, followed by light irrigation for a few weeks to allow swift establishment. If a no-till slice seeder is used to reseed the lawn, the dead mat of turf and nimblewill may readily serve as mulch material.

Recommendations for the use of agricultural chemicals are included as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services does not imply endorsement by West Virginia University Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

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