Looks like annual bluegrass complete with seedheads. Make sure your bermuda is completely dormant before you use round-up. Try using a dabber and saturate the bluegrass without getting it on the bermuda. With the seed production of the bluegrass, make sure you use some sort of crabgrass control throughought the season. Even go longer into the fall. That's is when the seed will germinate is in the fall. Annual bluegrass is a biennial. Germ in the fall, over winter, and grow and florece in the spring.

The reason your crabgrass preventer didn't work is that this stuff is a perennial that lives through the winter, it just goes dormant when it's cold. You have to kill it or dig it up completely, then use the preventer to stop the seeds from sprouting. You could just kill it now with Roundup instead of waiting for fall like I did, since you only have a few patches of it. I had it all throughout the lawn and it would have looked really terrible if I had sprayed during the growing season. It is not a type of crabgrass but the crabgrass preventer works on the seeds. Crabgrass is an annual that dies in winter so it's not as hard to get rid of as Dallis grass. There is an organic prevention that you could also use called corn gluten meal. I used to buy it at the feed store but they stopped selling it so I have been using the crabgrass stuff. The CGM sold as fertilizer is muy expensive compared to the animal feed version. But you still have to kill the plants that are already growing, it only works as a pre-emergent herbicide to prevent seed sprouting.

Do they bloom with a yellow head? Sorta look like goldenrod.

As was said, it's bittercress, the genus name Cardamine. And the pods explode to shoot the seed a number of feet away from the plant. Best remedy is to pull and trash or burn every plant you can locate. Then go over the area a week later to get those you missed. Then repeat. You can get ahead of it. (I'm slowly gaining on mine.) But you will need to be persistent for a number of years. Lots of seeds haven't yet germinated.