Physical removal is probably the best approach followed by filling the holes with compost. Dallisgrass can also be rotted to death with a heavy (at least 1/8" across the entire clump) treatment of sugar, dry molasses or cornmeal. It can also be sprayed with full strength vinegar. Add an ounce of orange oil and 1 teaspoon per gallon of vinegar for even better results.
The commonly recommended toxic chemical product MSMA is an arsenic compound and of course should never be used. Dallisgrass is a high-successional tough perennial grass that doesn’t go away when the soil is improved. In fact, it likes it. It’s a good forage for cattle, but that doesn’t help the home gardener. Applying corn gluten meal at 20 pounds per 1,000 square feet prior to seed germination in the spring is also helpful in preventing new plants.