I have had luck and others have reported success killing nutgrass with kindness. Mow, clip or pull as often as you can and apply a heavier than normal application of dry molasses. Use about 20 lbs per 1000 sq ft and repeat in two weeks. The mixed products that contain molasses, and cornmeal will also help. The idea here is to stimulate a furious level of biological activity aimed at rotting the crowns of the undesired plants.
We used to say that there's no good organic or toxic chemical solution for nutgrass. On the toxic chemical side, that’s true. The commonly recommended chemicals are Image and Manage. Most everyone in the landscape industry agrees with me that Image doesn't work on one of the most common species. Manage works better but will severely damage or kill your trees.
Another remedy is to remove the weed physically with mechanical devices. In beds cover the weeds with newspaper and mulch. Spot spray with the vinegar herbicide formula or Avenger. For turf, overseed problem areas with ryegrass in the fall. Applying corn gluten meal in the spring at 20 pounds per 1,000 square feet prior to seed germination is also helpful. An important point to remember is that nutgrass (nutsedge) grows primarily in wet anaerobic soil. Try applying hydrogen peroxide, the kind at the drug store, full strength to the problem areas. Also let the area dry out better between waterings, improve soil health , improve drainage and help the soil to drain better.
The best control appears to be molasses, believe it or not. Drench problem spots with liquid horticultural molasses at ¼ to ½ cup per gallon of water. Start with about a gallon of drench per 9-10 sq ft. This simple technique fires up the microbes in the soil and the nutgrass simple fads away.
Nutgrass Cyperus rotundus and ciesculentus are perennial sedges introduced from Eurasia. It spreads by seed, nutlets and creeping tendrils. Likes wet soil and is hard to control.