Green foxtail (Setaria viridis) is also known as “green bristle grass,” and little wonder. This common grass has a peculiar upright or nodding cylindric inflorescence covered in bristly hairs. The inflorescence is green on the whole, but often has a purplish tint. It varies from one to five inches in length and can be up to an inch wide. Because of the unusual shape of the inflorescence, it is tempting to classify it as a spike, but it is actually a panicle with many branches—the branches are just very short and hard to find without dissecting the plant. Mutant green foxtail plants with forked inflorescences have been seen in west-central Kansas, and possibly further east, as well.
The hollow stems are erect, allowing the plant to stand anywhere between 8 and 36 inches high. They often bend near the base at the nodes, and they may branch at the base, as well.
The leaves are 2 to 10 inches long and less than 1/2 inch wide. They can be either flat or folded and taper to long points. The leaf blade is hairless or very nearly so. Where the blade joins the stem, the sheath is fringed with hairs. This species has no auricles, earlike appendages growing at the junction of the blade and the sheath.
Green foxtail is a clump-forming grass. It grows a fibrous root system.
Common throughout the United States and all parts of Kansas, green foxtail is something of an opportunist. It can grow in any open area with adequate soil drainage and fertility, whether that is a lawn, a cultivated field, or a waste area. It prefers full sun, but will grow quite nicely in partial shade.
Green foxtail is a warm-season annual. It germinates in the warmer months as soon as the soil temperature passes 60°F. It grows quickly, flowering anytime from July through September and producing literally thousands of seeds. Some of the new seeds will sprout to produce new plants as the summer progresses. However, all existing plants are killed by frost, making the soil seed bank the sole source of plants the following year.
This species is not native to the United States and is considered a weed. It is a pioneer species in freshly disturbed areas. It also provides food for birds in the form of seeds.
While young green foxtail plants have some forage value, they are generally a sign that something is wrong with the pasture or hay field. Properly managed grass stands should be able to compete by shading out the foxtail.
Green foxtail is a problem weed in everything from fields to lawns. It robs desirable plants of moisture and nutrients, and it spreads foxtail mosaic virus, a disease to which sorghum is susceptible. Fortunately, green foxtail is easily prevented from establishing itself by attention to two priorities:
- Preventing the spread of seeds.
- Keeping a thick stand of desirable grasses or crops.
To prevent green foxtail from gaining a foothold, pay attention to such practices as rotating cash crops and preventing livestock and mowers from cutting the grass too short in pastures, hay fields, and lawns. In infested lawns, weekly mowing is recommended to keep the foxtail from producing a mature seed crop.
As the name suggests, giant foxtail is a taller plant than green foxtail, but there are other differences. Giant foxtail has hairy leaf blades and smooth leaf sheaths—the opposite of green foxtail, which has smooth or nearly smooth leaf blades and hairy margins on the leaf sheath.
Yellow foxtail is very similar to green foxtail; the differences between the two species are subtle. Yellow foxtail has a flat stem, leaves that sometimes (but not always) grow in a loose spiral, and long hairs often compared to cobwebs on the base of the leaf blades. If you are ambitious enough to count the bristles growing at the base of each spikelet of the inflorescence, you will note that yellow foxtail has 4 to 12 yellowish bristles compared to the 1 to 3 green or purplish bristles of the green foxtail.
Parts of a Grass Plant: A Glossary
Definitions for technical terms used in this post.