Yes and no. Topgrowth in zone 6 is probably going to be over very soon, and using a fall fertilizer probably won't have much effect. Now there are studies however that say applying a fast acting fertilizer (urea based) after topgrowth has stopped will help the roots and offer some more carbohydrate storage. So if you are going to do it, wait till your grass just stops growing and apply a high N, fast acting fertilizer.

Good advice from tiemco.

But, note that the rate for such last fall feedings is 1 and quarter pounds of nitrogen per thousand cubic feet. Keep in mind that isn't much volume when you are using straight urea.

And, water it in well.