Although lush green in appearance, nut sedge grass is not a grass at all. Sedges (Cyperus spp.) have grass-like leaves that more resemble the thin, lance-like leaves of lilies. Because sedges are thought of as grass and treated as such, the usual landscape herbicides have little to no effect. Sedges require a selective herbicide that acts on them specifically, causing no harm to the grasses with which they are intermingled.
Identify the species of nut sedge you wish to eradicate. Dig up or cut a sedge plant sample that includes leaves and, ideally, flower and seed heads and take the sample to a turfgrass professional at a landscape supply company, garden center or cooperative extension office. Knowing the species can better identify the best treatment for eradication.
Check the soil moisture in the area of the nut sedge infestation. Reduce irrigation in this area to impede the growth and germination of new sedges by creating drier soil conditions.
Purchase a selective herbicide known to be effective on sedges. Begin referring to this weed as a sedge and not a grass to avoid getting poor recommendations from people regarding the appropriate herbicides. Some chemicals known for efficacy in killing sedges include MSDS, halosulfuron and imazaquin. The product names include Sedgehammer, Image and Certainty, among others.
Follow the product label directions to determine application rates, dosages and timing. Wear long pants and closed-toe shoes and any other protective clothing advised on the product label.
Repeat the application of herbicide as recommended in the guidelines on the product label. Be prepared to follow up with a second and third application to effectively knock back and kill all sedge plants in the weed-infested area.