Green foxtail (Setaria viridis)

Synonyms: Panicum viride, Chaetochloa viridis

Common Names: Green bristlegrass, wild millet, green millet, pigeon grass, bottlegrass

Description:

Green foxtail (Setaria viridis) is a bristly summer grass from Europe, North Africa, and Asia that has spread across North America as a common weed of lawns, gardens, farm fields, and roadsides [1][5]. MISIN tracks it because it grows fast and produces huge numbers of seeds, letting it crowd into disturbed ground and crops ? though it is mostly a weed of cultivated and disturbed places rather than high-quality natural areas [2][5].

Habit:

Green foxtail is an annual grass ? it sprouts, seeds, and dies in a single season [2][5]. It grows in clumps of upright to leaning stems, usually about knee- to waist-high [2]. Its leaves are flat, light green, and rough to the touch, and the plant is topped by the feature that gives it its name: a dense, bristly, cylindrical seed head shaped like a fox's tail [2]. From summer into fall, this green (sometimes purple-tinged) "foxtail" spike stands 1 to 4 inches long and usually nods over at the tip [2][3]. It is easiest to identify from midsummer through fall, when the bristly seed heads are out [3].

At-a-glance cues:

1. A dense, bristly, cylindrical seed head shaped like a fox's tail, 1 to 4 inches long [2]
2. The seed head is green (sometimes purple-tinged) and usually nods at the tip [2][3]
3. Flat, light green leaves that feel rough to the touch [2]
4. An annual grass in clumps of upright to leaning stems, knee- to waist-high [2]

Leaves: Alternate, 1.5-12 in. long, lance-linear, flat, hairless, smooth to slightly rough, 4-25 mm. wide depending on variety, sheath is open, green in color, hairless except for a fringe of hairs along edge, Ligule is a fringe of hairs 1-2 mm. long. Hairless and green to purplish nodes.

Stems:

1. Habit: herbaceous annual grass; smooth, round stems, upright to leaning, that can root at the lower joints where they touch soil [2]
2. Height: usually about 1 to 3 feet tall, sometimes taller in rich soil [2]
3. Form: clumped and multi-stemmed [2]

Flowers:

1. Type: tiny grass flowers packed into a dense, bristly, spike-like head (a "foxtail") ? not showy petals [2]
2. Color: green, sometimes tinged purple [2]
3. Bristles: 1 to 3 slender green or purple bristles rise beside each seed, with tiny upward-pointing barbs [2]
4. Shape and size: a cylindrical spike 1 to 4 inches long that usually nods at the tip [2]
5. Bloom time: summer into fall, with seed heads mainly July through September [3]

Fruit and seeds:

1. Fruit: a small, dry grass grain (seed), oval and slightly flattened [2]
2. Seeds: one plant can produce very large numbers of seeds in a season [2][5]
3. Dispersal: seeds drop from the head and are carried on mowers, shoes, clothing, animal fur, and in moved soil [3]
4. Ripening: from midsummer into fall [3]

Habitat:

Green foxtail is native to Europe, North Africa, and Asia, and was introduced to North America, where it now grows across the continent [1][5]. It is a plant of open, sunny, disturbed ground ? lawns, gardens, farm fields, pastures, roadsides, vacant lots, and construction sites [2][5]. It does best in poor, disturbed soil and tolerates both moist and dry conditions [2]. It is a well-known weed of grain and row crops such as corn and soybeans, but it usually does not push far into high-quality natural areas [2][5].

Reproduction:

Green foxtail spreads only by seed, but it does so in huge numbers [2][5]. A single plant can make very large numbers of seeds in one season, and because it is a fast annual, it can produce more than one generation in a single summer [2]. The seeds are easy to move around by accident ? they hitch rides on lawn mowers, shoes, clothing, and animal fur, and they travel in soil moved from place to place [3]. Seeds sprout in spring and summer on warm, bare ground, and the plants set seed from about July through September [3]. The best time to act is before those seed heads ripen ? pull, cut, or mow the plants before the bristly heads turn brown and drop seed [3].

Impact and Damage:

For homeowners, green foxtail is mainly a lawn and garden weed [2][3]. It moves into thin or new lawns, garden beds, and disturbed soil, where its fast growth and heavy seeding let it crowd out grass and young plants [2][5]. Its bristly seed heads can also work into the fur or paws of dogs and other pets, so they are worth clearing from areas pets use [3]. The plant itself is not known to be poisonous, and grazing animals will eat it [2].

Green foxtail is best known as an agricultural weed, competing with corn, soybeans, and other crops and reducing yields [5]. In natural areas it is much less of a threat ? it favors already-disturbed, open ground and usually does not invade high-quality habitats, though it can be common along trails, roadsides, and field edges [2][5].

Similar species:

Green foxtail belongs to a group of grasses called foxtails, named for their bristly, cylindrical seed heads. Telling them apart comes down to seed-head size, bristle color, and where the leaves are hairy.

Yellow foxtail (Setaria pumila) is the most common look-alike ? a very similar summer annual foxtail grass [3][4]. Its seed head is yellowish to orange-tinted with shorter bristles, while green foxtail's head is green with longer bristles [3][4]. Up close, yellow foxtail has long, sparse hairs at the base of the upper leaf surface, whereas green foxtail's leaf blades are hairless but have fine hairs along the leaf sheath [3][4].

Giant foxtail (Setaria faberi) is a larger cousin with a longer, heavier seed head (up to about 7 inches) that droops or nods more strongly than green foxtail's [4]. Its upper leaf surfaces and leaf-sheath edges are noticeably hairy, unlike the hairless blades of green foxtail [4].

Monitoring and rapid response:

Signs to watch for:

1. Clumps of an annual grass with flat, rough, light green leaves in lawns, gardens, or disturbed ground [2]
2. Dense, bristly, green (sometimes purple-tinged) seed heads shaped like a fox's tail, nodding at the tip, from midsummer into fall [2][3]
3. New patches spreading along mowed strips, paths, and field edges [3]

What you can do:

1. Pull or hoe out plants while they are young and before the seed heads form ? this is the single most important step, because the plant spreads only by seed [3].
2. Mow or cut off the bristly seed heads before they ripen and turn brown, and bag them so seeds do not drop [3].
3. Keep lawns thick and healthy so there is little bare ground for seeds to sprout in [3].
4. Mulch garden beds and reseed bare spots to shade out new seedlings [3].
5. For a larger area, a crew can mow or cut before seed-set across the site and repeat over the season to keep new plants from seeding [3].

When to call a professional:

1. Large or repeated infestations in crop fields, pastures, or turf may need a coordinated plan over more than one season [3].
2. Because seeds build up in the soil, heavy infestations often take repeated effort to bring down [3].
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. USDA NRCS Plants Database. Setaria viridis (L.) P. Beauv. plants.usda.gov
2. North Carolina Extension Gardener Plant Toolbox. Setaria viridis (green foxtail). NC State Extension. plants.ces.ncsu.edu
3. Penn State Extension. "Lawn and Turfgrass Weeds: Yellow Foxtail and Green Foxtail." extension.psu.edu
4. University of California Statewide IPM Program (UC IPM). "Foxtails ? Weed Identification Gallery." ipm.ucanr.edu
5. Go Botany, Native Plant Trust. Setaria viridis (green foxtail). gobotany.nativeplanttrust.org

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