Virginia Tech Weed Identification Guide

Purpletop: Tridens flavus

Weed Description:  A perennial with short, thick rhizomes that is most noticeable from August through October when these plants reach 4 or 5 feet in height and produce dark purple panicles.  Purpletop is primarily a weed of hay fields, pastures, abandoned fields, and roadsides that is found from New Hampshire south to Florida.
Leaves:  Leaves are somewhat flattened and appear folded in the sheath and have a relatively prominent white midvein.   Leaves are 8 to 17 mm wide, usually hairy except near the bases, lacking auricles, and with a ligule that is a fringe of hairs less than 1 mm in length.

Stems:  Sheaths are round and usually hairy only near the top.   Plants may reach 4 to 5 feet in height when mature.

Flowers: The seedhead is an open panicle that is dark purple in color.  Individual spikelets are 6 to 8 mm long, 1 to 2 mm wide, and purple in color.

Roots:   Short, thick rhizomes occur along with a fibrous root system.

Identifying Characteristics:   A grass with relatively wide leaves that have a very small ligule that is a fringe of hairs.  Additionally, the short, thick rhizomes and purple seedhead are characteristics that help in the identification of this weed.