Thank you for learning the lesson about repeat applications of atrazine and posting it here. Sorry it had to be you, but thanks for posting. The effect of atrazine is not seen for several weeks, so you need some patience when using it. But once you see the effects, it seems to kill absolutely everything except the St Augustine.

I would definitely wait until at least April when all the weeds are up and growing and so is the grass. I'd wait until late April or even May with the double dose you did last fall. The weeds you have now are different weeds from what you took out last fall. Don't fret. What you have now is likely poa annua and possibly some wild flower plants. The clover you see is likely oxalis or black medic. Dichondra can be a bugger because it seeds so readily. We tried to grow it in SoCal when I was a kid and lost it every year to an insect called flea beetle. But it came right back from seed. Hopefully the atrazine will persist and work on the new dichondra sprouts, too.

Nutsedge is usually a problem in soggy soil. What is your drainage issue? Do you have low spots that need more soil? You could address the soil part of the drainage to a point with shampoo. Spray 3 or more ounces of shampoo per 1,000 square feet, follow that with 1/2 inch to an inch of water, and don't water again for at least a month (this time of year). Then this year, if you were not already, work on your deep and infrequent watering. Nutsedge does not like to dry out completely, so the deep and infrequent can severely cut it back. Nutsedge has a look-alike sedge cousin called green kyllinga. That plant looks like nutsedge until it flowers. Green kyllinga is not nearly as aggressive as nutsedge, but it is not affected at all by drought. I've seen it in spots that never get supplemental irrigation. Again, not as aggressive, but you don't want to walk on the new-mowed stems.

Where do you live?

Thank you for the great information. I am located in north Florida. I think by May it will probably be too hot here for atrazine application, so I may have to apply in April then. Just to be clear, I didn't do a double dose over the whole lawn, just a few spots where weeds came back, so I'll avoid those areas.

I think I just have terrible soil. It is sand for about 6 inches and then dense grey clay. We got about .5" of rain a week ago and I still have some parts of the lawn that are squishy when stepped on. I'll try the shampoo before the next rain. I'm not sure there is anything else I can do about it, the yard seems fairly level. I do have a neighbor that runs his sprinklers every day, so that could be causing some of the dampness. Surprisingly though, his grass always looks great.

What at do you mean don't walk on the new mowed stems?

When you mow sedge it leave very rigid stems that poke into your bare feet. They don't stab into you, but they are uncomfortable.

If you have a clay like layer under the sand, then your neighbor's daily watering could be running off of his property onto yours.

The neighbor's lawn could look fine, but it is what I would call fragile. Since the grass gets nearly continual water the roots do not have to grow long down into the soil. If one of his sprinklers breaks and turns into a geyser, that will cause the rest of the sprinklers to not apply enough water. The shallow roots will not be able to get water and the grass could quickly die or go dormant, depending on the grass. Whereas if you water deeply once a month in the cool months and once a week in the heat of summer, that forces the roots to grow down deep to get to the water. If your sprinklers break the grass will still be getting some moisture from the deep roots. Your objective is to get roots growing into the clay like layer to loosen it up. The shampoo should help with that along with deep watering.

Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall.