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Giant Foxtail (Setaria faberi Herrm.)

Also known as Japanese bristlegrass.

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An annual grass, native to East Asia and introduced in North America.

Range - Expand

Introduced or Not Present

This tentative map is based on our own research. It may have limited data on Canada and/or Mexico, and there is some subjectivity in our assignment of plants as introduced vs. expanded. Read more in this blog post.


Found in disturbed, sunny habitats, but adaptable to a wide range of moisture conditions and soil types.

Can compete somewhat against other plants of similar stature, but requires exposed soil to germinate, and intolerant of shading from taller plants.

In North America, mostly found in anthropogenic habitats, especially as a weed in agriculture, particuarly no-till agriculture, and along roadsides and railroad tracks, and other areas where other vegetation is removed before the start of the warmer part of the growing season, but not in areas that are mowed regularly. Often thrives in areas regularly treated with herbicide, especially where herbicides are applied only between late summer and early spring, outside this plant's growing season.

Life Cycle

This species is an annual that exclusively uses C4 metabolism, and it thus has a fairly short growing season restricted to the warmest months. Seeds germinate in late spring to early summer, in response to a combination of warm temperatures, moisture, and soil aeration. This species usually requires exposed conditions to germinate; it benefits from soil disturbance and cultivation. Germination is likely inhibited by cool temperatures, shading, drought, or poor soil aeration, but the mechanisms of this inhibition are poorly understood; the seeds may exhibit a type of secondary dormancy triggered by certain conditions.

Growth is rapid. Plants do not always support their own weight, and may fall over and sprawl if not supported by other vegetation.

Starts blooming mid-summer and continues into autumn, but plant growth slows as temperatures and sunlight decrease. Flowers are wind-pollinated. Seeds mature in late summer to fall. Both flowering and seed production is staggered, often varying from plant to plant, with seeds on some plants maturing before some plants have even produced flowers. Seeds on a particular spike also ripen inconsistently, with some ripening and falling off before others are ripe.

Seeds can form a persistent seed bank and may remain viable for many years. In habitats where it occurs, this species can be one of the more abundant members of the seed bank, but seeds do not germinate in all years because they are dependent on conditions. However, the seed bank can become depleted if germination is high in a particular year.

Populations vary considerably from year to year; this plant tends to do best in warmer years, and when rain is concentrated in late spring to early summer, followed by drier conditions later in summer. Earlier spring rain followed by a dry late spring to summer results in this plant struggling to establish and facing more competition during the period when it germinates. However, dry weather later in the growing season gives established plants an advantage against competing vegetation, from its C4 metabolism.


This species can be difficult to control because it is competetive against many grasses as well as crops.

Small isolated individuals growing in with other vegetation can be uprooted by hand. Uprooting is much easier if individuals are identified early in the season, as the root system is less extensive. Larger patches can be mowed or weed-whacked; this plant tends not to recover from mowing as it invests most of its resources in aboveground growth during the early part of the growing season.

On sites where this species is a persistent problem, one of the best ways to control it is to change the site's management regime, so as to prevent its germination and establishment. Mowing a site earlier in the year, such as in late winter, and allowing the establishment of competing vegetation in early spring, can hinder its establishment. Where large monocultures exist, mowing after plants are established, such as in mid-summer, can kill most plants and greatly reduce seed production if any plants survive. When the site cannot be mowed mid-season, such as in cropland, the use of low-growing cover crops, particularly broadleaf plants, can prevent seedling establishment.

Herbicide is often ineffective at controlling this plant, although it can be effective in some circumstances. This species tends to be resistant to a number of herbicides, including triazines, sethoxydim, fluazifop, diclofop, and it may also be resistant to alachlor, paraquat, linuron, and diuron. It is (currently) susceptible to most other herbicides although with all species that are weeds in commercial agriculture, resistance will likely only increase over time. Herbicide use is most effective on this species when it is carried out before seeds are produced, and when this species is growing in a large monoculture and not interspersed with desireable plants such as crops or native plants. Herbicide use can backfire if it kills perennial plants that would compete with this plant long-term, allowing it to re-establish in the next year. This species frequently thrives in areas treated yearly with herbicides, especially if the timing of treatment falls before germination and after seed production.


This species has negative impacts on native grasses that fill similar ecological niches, such as fall panicgrass (Panicum dichotomiflorum). However, it competes poorly with most broadleaf plants.

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