Also known as yellow nutgrass, this perennial weed thrives in moist areas in much of the country. Its bright green leaves grow from the base in groups of three; grass leaves, in contrast, grow in sets of two. The flower head is golden brown. Small, roughly round tubers (nutlets) form at the tips of the roots; the weed spreads by these tubers as well as by seed.
Remove nutsedge when it's young ― when plants have fewer than five leaves or are less than 6 inches tall. Older, taller plants are mature enough to produce tubers; when you dig or pull the plant, the tubers remain in the soil to sprout.
For chemical control, try glyphosate, being careful not to get the chemical on desirable plants. It is most effective when the plants are young; it will not kill tubers that have become detached from the treated plant.