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Weed Identification

Virginia Tech College of Agriculture and Life Science Virginia Cooperative Extension

giant foxtail

Family

Poaceae

Scientific Name

Setaria faberi
Weed photograph 1
Weed photograph 2
Weed photograph 3
Weed photograph 4
Weed photograph 5

Other Common Names:

Japanese bristlegrass

Habit

Pants germinate in spring and compete with crops during summer. Seed production starts in mid to late summer. Reproduces by seed. Plants grow in clumps and lack stolons or rhizomes, but have a shallow fibrous root system.

Leaves

Leaves are light green, up to 16in long and 1/2 to 1 1/2in wide at maturity, and have short dense hairs on the entire surface from tip to near the base. Sometimes leaves can look as if they lack hairs, but bending the leaf and examining the crest in sunlight will reveal the short hairs on the surface. Ligule is hairy (3mm) and plants lack auricles.

Identifying Characteristics

Plant height can reach 2-5 feet. Hairy ligule and leaves, but stems often do not have hairs. Plants lack auricles and do not have stolons or rhizomes. Plants have characteristic foxtail seed head that is long and nods (unlike other foxtails). Distinguishable from other foxtails due to its larger size, short hairs on upper leaf surface, and a nodding seed head.

Flower Seed Head

Seed heads are green in color. A bristly spike on the end of a long, slender, naked stem. Seedhead is typically long (~2 in) and nods (unlike other foxtails). Each spikelet is about 3mm long with up to 3 bristles that are 5-10mm long

Seed Fruit

Seed are 3 to 5 mm long and covered with upper and lower sheath (palea and lemma) that have pronounced veins. An average plant produces 900 seeds.

Where Found

Typically found in cultivated areas following a tillage event. May occur in open areas such as the border of rock driveways or in highly disrupted turfgrass. It is often found in highly fertile soils, especially soils high in phosphorous.

Leaf Hair on Upper Surface

hairs from base to tip

Leaf Arrangement

rolled in bud

Mature Leaf Width

Varies: 
less than 5 mm, 
6 to 15 mm, 
more than 15 mm

Stem

flat or oval

Seedhead

Varies: 
bristly, 
panicle

Root Structure

fibrous

Life Cycle

summer annual

Auricle

not present

Ligule

hairy

Ligule Length

Varies: 
1-2 mm, 
2-3 mm, 
more than 3 mm

Plant Type

Grass