Giant foxtail Setaria faberi Hermm.
Life cycle: Annual
Native status: Native to China
Habitat: Agricultural fields, disturbed habitats
General description: Largest of the three primary weedy foxtail species, can reach heights of four feet. Seedhead is a bristly, spike-like panicle that droops.
Key ID traits: Hairy ligule, upper surface of leaves is covered with a dense mat of short hairs that are easily visible when held to light. Seedhead typically droops more than 45 degrees.
Similar species: Yellow foxtail has sparse, long hairs at the base of leaf blade and an erect seedhead. Green foxtail has no hairs on leaf blade and a smaller seedhead which tip bends slightly.
Miscellaneous: Most Iowa crop fields have a mixture of giant, yellow and green foxtail. Giant is the predominant foxtail in most fields, but the proportion of green increases in northern areas of the state. Yellow foxtail often is more common in fields where farmers have relied heavily on postemergence herbicides (other than glyphosate). All were introduced to U.S. from China in the first half of the 20th century.