狗尾草（学名：Setaria viridis），又名绿狗尾草、谷莠子、狗尾巴草。一年生草本植物；秆直立或基部膝曲，高30-100厘米；叶片扁平，狭披针形或线状披针形；圆锥花序紧密呈圆柱形，刚毛粗糙，通常绿色或褐黄色。同属植物常见的还有：大狗尾草（Setaria faberi）等。

狗尾草是小米的祖先。

与之外形相近的**（原S.glauca，现Pennisetum glaucum）已经移入狼尾草属，与之非同属植物。

狗尾草的种子适生性强，耐旱耐贫瘠，在酸性或碱性土壤均可生长，常见于农田、路边、荒地。全球分布广泛，中国各地均有分布，为常见主要杂草。麦类、稻类、玉米、旱作物易受其侵害，与作物争夺肥力能力强，造成作物减产。

Setaria viridis is a species of grass known by many common names, including green foxtail green bristlegrass, and wild foxtail millet. It is sometimes considered a subspecies of Setaria italica. It is native to Eurasia, but it is known on most continents as an introduced species and is closely related to Setaria faberi, a noxious weed. It is a hardy grass which grows in many types of urban, cultivated, and disturbed habitat, including vacant lots, sidewalks, railroads, lawns, and at the margins of fields. It is the wild antecedent of the crop foxtail millet.