Ken

A picture of the weed that you are trying to get rid of would be helpful. Your two suggestions, Nutsedge or fountain grass, are totally different species. Fountain grass is a generic term for a large number of ornamental grasses that are popular plantings. Nutgrass or nut sedge however is a weed that grows from seeds and also spreads widely from rhizomes. It has V shaped blades and a starburst flower that develops into seeds. It is not affected by normal lawn herbicides and pulling the grass out does not stop the spreading since the rhizomes are deep in the lawn.

I will assume that nut sedge is the weed you are concerned with. If not, please send a picture of the nasty weed. 

There are herbicides that attack the nut sedge and another common lawn problem Kyllinga sedge. The active ingredient is sulfentrazone. One with a high concentration of this ingredient is Dismiss. There may be others. This is very expensive and is the reason the lawn company quoted a high price for the application. It is applied in a very dilute solution and is offered on the internet in more than one size container. It may be available at a lawn and garden store but I have not attempted to locate any. There are others more commonly found with sedge in their names which have not been as effective perhaps due to lower concentrations of the active ingredient or a less effective active ingredient.

A surfactant is recommended to help the product wet the blades. It is best applied to the grass before cutting and then allowed to act for a few days after the application before the next cutting. It may take another application in two or three weeks if the grass is not tuning brown. It may have to be applied again in the next growing season if some sedge grass reappears.

As with all products Read The Label before using and take precautions for contact with hands and face.

Thanks for using Ask Extension

Tony