Q: This weed has a spikey seedhead. It is growing wild in a liriope bed that is in full sun.

A: You have yellow nutsedge (nutgrass). The chemical imazaquin (click for sources) is labeled for use on some liriope varieties, and may be safe for all of them, but you’d better test it on a small patch of liriope before spraying the whole bed.

Imazaquin is absorbed by the roots so be sure to irrigate after application. In my experience, control is slow to appear. You won’t see damage to the nutgrass for several weeks.

see

Nutsedge Control in Landscapes