莠狗尾草（学名：Setaria geniculata）为禾本科狗尾草属下的一个种。

Setaria parviflora is a species of grass known by the common names marsh bristlegrass, knotroot bristle-grass, bristly foxtail and yellow bristlegrass. It is native to North America, including Mexico and the United States from California to the East Coast, Central America and the West Indies, and South America.