I always recommend just doing spot treatments for weeds - unless we are talking about a weed field that might have grass hidden in there somewhere.

Usually with dandilions you can just walk through the yard spot spraying (quick shot per) and the things turn out great. Not good to be throwing herbicides all over the yard just for items that are only in certain easily identifiable areas.

Of course there is the chance you will miss a few - but you can always hit them in a week or two if you don't see any death starting.

Where do you live? Everything should be going dormant in the US...unless you have fescue in the Southwest desert or the coastal Pacific.

Weed n feed is usually not a great idea. Fertilize with a real fertilizer and kill weeds with a real weed killer. There is a mechanical approach, too. There used to be only one standup tool on the market for plucking weeds but now there are others. The Weed Hound is one of them. You center the teeth on the weed and step on it. The tool plunges into the ground and grips the weed by the tap root. Then you lift it out and you have the whole thing.

In the future if you mow your fescue (assuming it is not a dwarf variety) at your mower's highest setting, and water infrequently (when the soil surface has been dry for several days), then you should never see another weed. There have been reports here on this forum where someone changed his mowing height and went from watering every day to watering once a week. His neighbor had an entirely crabgrass lawn but it stopped dead in its tracks when it hit the border with his dense, tall grass.

Oops! I just reread your first post and see that you live near the coast in SoCal and from your screen name, I'm assuming you live in Torrance. Then you definitely fall into the category of "able to grow fescue."

If you have dandelions they you must have some thin spots or you are mowing too short or you are watering too frequently or maybe a combination of the above. If you have thin spots, then you'll need to reseed. Assuming you have a variety of Marathon fescue, you should find out whether you have Marathon I, II, or III so you can get the right seed. They are all three dwarf varieties. If you have III, then you really are supposed to mow that short and you might be fighting dandelions forever. In Torrance you should be watering about once every 3-4 weeks all year long. For those of you who are reading that and are not from the SoCal area, temperatures in Torrance are cool every day. The sea breeze begins at 2pm and cools things off. During those 2 weeks when the Santa Ana winds blow, you can water every 2 weeks. This is likely very different from what you are doing presently. When you do water, water a full inch at a time so it soaks in deep. If you get runoff before you get an inch of water, then stop and let it soak in for 30 minutes. Then resume until you get the full inch. After you water deeply for several cycles, the soil should become more receptive to receiving all the water at one time. Watch your grass as you wean it off of a more frequent watering cycle. Watch it for drying out. As soon as it appears to be drying out, water it again deeply. Then restart your calendar aiming for once every 3-4 weeks.

If you want to spray your current crop of dandelions, I believe you can get Weed-B-Gone in a hand sprayer bottle. That's all you need. Spray each individual weed to moisten the leaves. It is not a soil drench.