Swamp grass is a common weed throughout the United States and is more commonly referred to as nutgrass or yellow nutsedge. The weed is very hard to control, propagating rapidly from seed, rhizomes and hard tubers called nutlets. Under optimal growth conditions, a single tuber leads to nearly 2,000 new plants in one growing season.
Irrigate the weedy area well a day prior to herbicide application. Water enough to moisten the soil as deep as 6 inches.
Use glyphosate as an effective post-emergence control of swamp grass, as recommended by the University of California Extension. The chemical is sold under different trade names.
Spray herbicide on each weed to cover the plant well. You don't have to drench the weed to the point of runoff. Swamp grass is best controlled during its active growth stage between early spring and early summer, according to Trey Rogers in Lawn Geek. Avoid applying any chemical if air temperature exceeds 85 degrees F.
Wait for two days after herbicide application before watering treated area again. Irrigate well so that soil is moist to a depth of about 6 inches.
Irrigate area deeply again after a week and reapply herbicide. Water well after two days, drenching the treated ground to a depth of six inches. Swamp grass is hard to get rid of and often requires up to four application before total elimination.