The seed leaf (coleoptile) of yellow foxtail is pale green, less than 1/8 inch (3 mm) wide, and up to two inches (5 cm) long. It usually has a few cobwebby hairs on the upper surface near the base of the leaf blade, but these hairs are more conspicuous on true leaves. True leaves of yellow foxtail are rolled in the bud and taper evenly to a point. ln seedlings it is difficult to see the ligule—a fringe of hairs about 1/32 inch (0.5 mm) long. Ligule hairs are fused together at the base.
1. Seedlings have cobwebby hairs near the collar.
2. Fringed ligule surrounded by wispy hairs.
Leaf sheaths are smooth and distinctly flattened, usually green, and often purple-tinged, especially near the soil surface. Sheaths are split and the smooth transparent margins overlap in front. The back edge of the leaf sheath is sharply keeled, or folded along its length, forming a flattened, creased stem.
3. Leaf sheaths are flattened, leaf blades are hairy near the collar.
Yellow foxtail is a shallow-rooted summer annual grass that reproduces by seeds. Stems grow 1 to 2 feet (30 to 60 cm) tall and branch at the base. The grass tends to grow in clumps because the stems often tiller, or root, at the lower joints.
Stems are smooth, and leaf sheaths are smooth and flattened; the back edge forms a sharp crease, especially at the base of the plant.
The ligule of the mature leaf blade is a fringe of hairs about 1/16 inch (1 to 2 mm) long. The hairs of the ligule are fused together near the base. Auricles are absent.
4. Leaf blades often twist in a graceful spiral.
A major identifying characteristic of yellow foxtail is the straggly white hairs clustered near the base of the upper leaf surface, as described under the Similar Species section. Except for these long hairs near the collar, the leaves are smooth above and below.
Leaf blades are 4 to 12 inches (10 to 30 cm) long and about ¼ inch (6 mm) wide at the base. They broaden slightly up to the midpoint, then taper evenly to a pointed tip.
The seedhead (panicle) is a compact, slightly tapered cylinder covered with soft yellow bristles (awns) about ¼ inch (6 mm) long. The erect panicle grows 1 to 5 inches (2 to 12 cm) long and ½ to ¾ inch (1 to 1.5 cm) wide, including the awns.
5 . Mature plant in seed.
6. Seed head showing yellow bristles.
The small seeds are densely packed along the main axis of the panicle. Since they do not require a dormant period, they can germinate as soon as they mature. Seedlings can grow to maturity and produce seed in forty days or less. Seeds germinate at temperatures between 68° and 95°F (20° to 35°C) and at depths of about ¾ to 1¼ inch (19 to 30 mm).
Originally introduced from Europe, yellow foxtail is now found throughout the United States and much of Canada. Somewhat less common than green foxtail, it occurs in the same areas, competing most heavily in cereals, vegetables, in row crops such as com and soybeans, and in orchards and vineyards.
Like green foxtail, yellow foxtail has value as a forage. However, it is usually not encouraged in well-managed fields because it can crowd out more desirable plants. In addition, the barbed awns can cause abscesses and infections by lodging in the mouth, nose, and eye tissues of livestock.
In addition to competing with crops for nutrients, yellow foxtail can cause abnormal growth in certain crops, including corn and some vegetables. Research on cabbage and tomatoes shows that foxtail may be toxic to crops. Toxicity occurs when chemicals produced by the foxtail roots travel through the soil and are absorbed by the roots of vegetable plants. This interaction, called "allelopathy," enables some plants to reduce competition by stunting nearby vegetation.
The genus name Setaria derives from the Latin seta, meaning "bristle." Yellow foxtail may be referred to by one of two species names, glauca or lutescens, both referring to a pale yellow color. This weed is also known as yellow bristlegrass and pale pigeon grass.
Three Setaria species are common in the United States: yellow, green, and giant foxtail. The yellow variety is the easiest to identify because of the cobwebby hairs near the base of the leaf blade. Hairs grow up to 3/8 inch (9 mm) long and may be either sparse or dense enough to obscure the ligule. The rest of the leaf blade is hairless. Mature yellow foxtail leaves often twist in a loose spiral, while those of the other species tend to be flat.
Green foxtail (S. viridis) leaves are completely smooth or have a few short hairs 1/16 inch (1.5 mm) long scattered along the upper surface. They never have the long white hairs characteristic of yellow foxtail. The entire upper leaf surface of giant foxtail (S. faberii) is densely covered with soft, short, velvety hairs 1/16 inch (1.5 mm) long.
The seedheads (panicles) of yellow and green foxtail are similar in size and shape, but not in color. The bristles (awns) on the seeds of yellow foxtail are yellow, while those of green foxtail are green or purple. All foxtail panicles turn tawny yellow when dry.
Important identifying characteristics of yellow foxtail include the long hairs near the leaf base, the smooth flattened leaf sheath, spirally twisted leaf blade, short hairy ligule, and yellow awns.
Since seeds can germinate over the entire summer, full-season control of this weed may be difficult. Most preemergence herbicides are effective in controlling foxtail if applied at the recommended time and rate. Herbicides applied very early in the season often lose their effectiveness by the time foxtail germination is at its peak. As a result, foxtail can be a problem in early planted fields.
Row crops, such as soybeans and com, favor the growth of foxtail. Therefore, a rotation that includes a solid stand crop such as legumes or grasses can help keep this weed under control. Mowing before seed production is a cost effective way to prevent the spread of foxtail in solid-stand forages. A combination of cultural and chemical methods is recommended for avoiding foxtail problems in row crops. Cultural methods include planting narrow rows and providing the nutrients necessary for vigorous crop growth and early canopy closure.
For specific recommendations, consult your county Extension agent or the most recent Weed Control Manual and Herbicide Guide, available through Meister Publishing Company, 37841 Euclid Avenue, Willoughby, Ohio 44094. Follow label instructions for all herbicides and observe restrictions on grazing and harvesting procedures.
Prepared by W. Thomas Lanini, Extension weed specialist, and Betsy Ann Wertz, agricultural writer.
Weed Identification 14