What is nimblewill?

Correct nimblewill identification saves a lot of wasted effort, because this grassy weed doesn’t respond to ordinary weed-and-feed products. It’s a perennial warm-season grass native to eastern North America, Pennsylvania included.

Pennsylvania lawns are mostly cool-season grasses like Kentucky bluegrass, tall fescue and ryegrass that grow best in spring and fall. Nimblewill does the opposite: it greens up late, grows hard in summer heat, and goes dormant early in fall. That leaves tan, wiry patches in your lawn for half the year.

It spreads slowly by thin runners, so a small patch gets bigger every season if nothing pushes back.

Nimblewill identification: what to look for

• Blades: short, usually under 2 inches, flat and pointed. They’re blue-green to gray-green and stick out from the stem at wide angles.
• Stems: thin, wiry and springy, with obvious joints. Patches feel fluffy or spongy underfoot.
• Ligule: a very short, jagged membrane where the blade meets the stem.
• Runners: weak, thin stolons that creep along the soil and root at the joints.
• Seedheads: very slender spikes from midsummer into October, with tiny seeds carrying long, hair-like awns.
• Dormancy: stems turn pale, straw-colored and stay that way through winter until new growth emerges from the crowns in late spring.

The easiest time to map nimblewill is early spring or late fall, when it’s tan and the rest of the lawn is green.

Where it grows in Pennsylvania

Nimblewill is common in home lawns, parks and other low-maintenance turf statewide. It’s unusually adaptable, growing in sun or shade and in wet or dry soil, which is part of why it’s so persistent.

You’ll often find it in shady lawns under trees, along wooded lot lines and in thin turf that gets stressed in summer. When bluegrass slows down in July heat, nimblewill takes advantage and spreads.

Many homeowners first notice it after a dry summer. Bluegrass goes dormant in drought, but nimblewill tolerates it and stays green, so the patches look healthy in August and then turn tan when the rest of the lawn recovers in fall. Seed and runner pieces also ride along on mowers and in topsoil, so a patch can show up in a lawn that never had one.

Nimblewill look-alikes

Creeping bentgrass is the most common mix-up. Bentgrass also forms fluffy patches, but it stays green in cool weather, has softer, thicker stems and a noticeably longer ligule. Bermudagrass also goes dormant and tan, but it has a hairy ligule, thick runners above and below ground, and finger-like seedheads.

Japanese stiltgrass grows in similar shady spots, but it has wider, lance-shaped blades with a silvery stripe and dies each year.

How to get rid of nimblewill

Expect a multi-step, multi-season job. Most broadleaf weed killers do nothing to nimblewill, and many crabgrass products don’t touch it either.

• Hand removal: for a few small patches, it pulls out easily because the roots are shallow. Do it after it greens up and before it sets seed, then rake and reseed the spot.
• Selective herbicides: Penn State lists mesotrione and topramezone as selective options that spare most cool-season grasses. They turn the nimblewill white and kill it slowly over a few weeks. Expect two or three applications during active summer growth.
• Spot spraying with glyphosate: works on patches you plan to reseed, but it kills the surrounding lawn too. Spray actively growing plants in summer, let it regrow, and treat again. Then overseed.
• Reseed after treatment: late August into September is the best time in central PA to seed cool-season grass into the treated area. Check your herbicide label for any waiting period before seeding.

With any herbicide, read and follow the label (the label is the law) and confirm it’s labeled for your grass type and site. Applying herbicide for hire in Pennsylvania requires a PA Department of Agriculture pesticide applicator certification. Selective nimblewill products are often best left to a licensed lawn-care company.

Keeping it from coming back

Strong cool-season turf is your best defense. Raise the mowing height to 3 to 3.5 inches, fertilize mainly in fall and overseed thin areas every year or two.

Clean mower decks and avoid moving soil from infested areas when you renovate. Where shade under trees keeps turf thin, consider shade-tolerant fine fescue or converting the toughest spots to a mulched bed. Keep an eye on patches in early spring and late fall, when they’re easy to see, and handle any small ones before they grow.

Be patient with treated areas. Plan on a season or two of follow-up, because a few runners usually survive the first round. Spotting and handling those leftovers early, while the patches are small, is far easier than starting over.

Questions we get about nimblewill

Similar weeds

Creeping BentgrassAgrostis stoloniferaBermudagrassCynodon dactylonJapanese StiltgrassMicrostegium vimineum