Yellow Nut Sedge (cyperus esculentus): This is a perennial weed that spreads both by seed and by underground runners. It grows best in full sun and disturbed soils. It spreads quickly, so pull it out now! Cut the seed heads but pull after. You will have to treat herbicides next year. Evil weed. It also produces 'nutlets' in the ground that will reproduce next year, not grass!